Hot restart issues
 

I know, not a new issue for a novice user to have but I was hoping someone could point me in the right direction. I've been struggling with this for awhile now and I've been reading and watching the how-to video on this page. I think I've made decent progress but the hot starts have me baffled. I know it's just my lack of understanding all the nuances of tuning but I'm doing my best to learn as much as I can. Right now my cold start is good. The car warms up fine and idles good when warmed up. Car runs well and the AFRs seem good. It's the hot restarts that are giving me fits. The car just stumbles and doesn't start unless I get on the gas. Now the fact I need to give the car gas should be a clue but I've adjusted the ASE and ASE Taper with no success. Some background on the car. 97, stock motor with an MS3 Pro pnp from DIYAutotune. I have deleted the MAF and installed a GM IAT. Recently I installed Flow Force 640cc injectors and a DW200 fuel pump, adjusted the Req fuel and dead times. I am taking these steps to eventually install a BRP MP62 which I already have. I've included my current tune. Appreciate any advice.

Post a log. Preferably 2 logs. One with a good start cold and one with a bad start hot (no throttle).

1st thing I whould do is multiply all of your MAT correction curve by 0.855 (1/1.17) and all of your VE table [and idle VE table] by 1.17. That way you are proper referencing a more normal air temperature while tuning, and the curve makes sense to other looking in. That is not your problem, just a little something that needs cleanup.

Here you go. It was about 50F in my garage. The cold start log is the car idling up to temp (about 190F). The hot start log is about 20 minutes later. You'll see the initial start fail. The second try it catches, and eventually evens out. It actually started better than yesterday but it's cooler out tonight. I physically felt the IAT and it was not as hot as yesterday. Probably because I didn't drive the car and just idled up to temp parked.

Cold start log was too big so it's on my server at work. Just grab it from the URL below. Thanks.
cold start log

Items you have that are contributing to your issue:

• As I mentioned in post #2, you need to adjust your MAT correction and VE tables so the MAT makes sense. Then, if you want to combat a FALSE MAT reading at a hot restart, Ignore MAT will ADD fuel, not pull it.
• Advance in idle area (you are not using Idle Advance) swing 10* from 25 to 40kPa. That, with your idle advance correction, is giving 15* swings. This is causing the up and down.
• Your MAT corrections, as mentioned before, are all above 100%. Then you have chosen to Ignore MAT during ASE, which means you are pulling 17%+ fuel during ASE due to that setting.
• I don't think you have calibrated WUE. There is a wizzard for that. At cold, you are really rich; at least in terms of 12.5 AFR. Maybe NA's need that, IDK.
• Use the re-scale function to create Ignition Table bins similar to the ones in your VE table. In anticipation of Boost. Unless you just want a straight linear from 150 to 200 kPa.
• Turn on EGO at lower CLT. I use 70*

Thanks for the advice. I hope I can get some time this weekend and try to clean things up. I didn't make the changes yet that you pointed out in message #2 since I didn't want to make changes and have the tune different than what I posted. I suppose I could have re-posted the tune but just wanted to maintain the baseline for the thread. Question on that... I can see why my MAT correction would need adjustment. I was playing around with that and it's messy at the moment but I don't understand multiplying the VE table by 1.17. Do you mean all the fields or just the X, Y axis and then reinterpolate?

Look at the fueling equation. It includes MAT Correction and VE as multipliers (along with MAP, and a few other items).

If you divide all MAT corrections by 1.17 and do nothing else, then immediately every fueling point (save Crank and Priming pulses) will be lean. To keep you where you have already tuned, the VE must be increased by the inverse of the amount MAT is decreased.

That is true except during ASE, where you would then be richer than you have been.

I suggest you fix that issue by turning off the "Ignore MAT during ASE". Use that as a last resort later if you need to.

Best of Luck

DNM

Ok, I see now. Thanks for you patience and advise.

Since I have just begun messing with the MAT correction would it be a better strategy for me to just set the fields all to 100 so it's not doing anything, work out the other issues that where pointed out and then start adjusingt the MAT as needed ?

If you wish. Still have to compensate for the change in the correction that MAT is presently giving. I would still suggest doing so in the VE tables.

The shape of your MAT table is not bad, however. It is just all one-sided. If you zero it, then tune VE some in the morning at 70*, and then some at afternoon at 85*, you will fight yourself; showing rich in the evening, lean in the morning. As long as you tune VE while running at the same MAT temps, and then later tune the MAP table, no worries. Just realize the interactions of the various components of the tune.

Thanks again. You hit the nail on the head here. My inexperience with the interaction of all the different settings has probably been the biggest challenge for me.

DNM,

Sir, you have always provided sage advice here. Can you tell us why there isn't a universally approved MAT correction curve?

I think, like many things, there can be general rules of thumb, but every installation is unique. Also, I can say what approach I took to tuning MAT CORR (MC) and what results I got and use, but have no other tunes / results to compare against.

Theoretically, the correction should match the ideal gas law. In that case, the corrections at Tnow from Tbase are (Tbas+460)/(Tnow+460): Tnow = the temp under review, and Tbase being the 100% CORR temperature. For less confusion in tuning (as I mentioned above) Tbase should be around your typically experienced value. For me that is 70F.

How should that be applied. Well, to be valid: 1) The measured temp should be the actual air temp; 2) the temp must be measured at the same location that the MAP sensor is measuring the pressure.
Meeting (1) is difficult under certain circumstances due to what is known as Heat Soak. Meeting (2) is related to (1). Ideally you would want the MAT sensor to be in the intake manifold. However, the pick-up of heat from the IM into the sensor has been known to give false readings. So, to combat those things, on a Turbo car, the consensus it to place the sensor on the outlet of the FMIC. There, it is shielded from the engine heat and gets a good read on the air temp just before the throttle.

What is the negative of this? It is before the Throttle, and therefore will not take into account, under most circumstances, for air temperature drop due to throttling, so that it is not seeing the temp of the air as it the temp where the MAP sensor is reading absolute pressure.

So: When I tuned my MC, I did not use data when my throttle was opened less than 40%. The goal was to have the measured air temp be very close to the air temp within the IM. The implications are that the MC are valid for MAP of about 80kPa and above, but not correct for cruise. For me that is what we want. We want very little EGO correction in boost, and more EGO correction available for lower kPa. That is what we end up with. When I tuned MC at cruise, I would go rich as my MAT increased with long, hard pulls. I pulled fuel in the upper right of the VE table. Then in cold weather, I would go lean up there. That is why I suggest tuning MAT corrections up top.

Maybe people don't care, because they want richer AFR when MAT is higher? I guess that would help with detonation? IDK. I'm just giving my philosophy, which is to not need EGO to hit my prescribed AFR table values.

My resultant table was not the full Ideal Gas Law corrections. About 5% less in each direction.

Some people, to combat Hot Restart issues, flatten the top of the curve. However, realize that is only a true fix for that one condition, when MAT sensor is really heat soaked. By that, I'm not saying it does not work, even if the sensor is not heat soaked, only that it is a fix that is compensating for another issue, rather than correcting for the actual issue. By placing the MAT sensor on the FMIC, away from radiator and engine heat, one should find little true heat soak of said sensor. I believe the writer of the TS manual called it "perceived heat soak". Also, I hesitate to compromise 99% of running time tuning to fix a problem that occurs for 1 minute of run time, at a non-critical time. Afterstart vs running in boost.

That all being said, here is my table:
https://cimg8.ibsrv.net/gimg/www.mia...aefb39984f.png

The ideal gas law would put the 15*F correction at 111, where I am at 108. (the 0* is prediction, and I have never run the car that cold). Note that my Tbase is 70*, where I am at 100%.
The ideal gas law would put the 140*F correction at 88, where I am at 92.
So, I'm lower correction at both extremes, but far from flat.

DNM

Regarding warmup AFR, there's a really cool table hidden in VEAL menu, under WUE, advanced settings. It's a curve to keep AFRs lower during warmup rather than targeting your warm running ~14.7 AFR. Personally I think a car starts really well with a few seconds of 11.0, and then warm up around 12.5 until ~140 coolant, then tapering from 13.5 to 14.5ish hot.

OK. That is cool, and great to know. I have personally been happy with 14.7 after ASE, except for 1st drive off, things go lean, and I have not been able to combat that with EAE, as it lasts about 3 seconds. More related to time after start than absolute CLT. Still, this could help. I understand that often OEM's runs richer (not just extra WUE) during warm-up. @BBro may be interested in this as well.

PosCat given.

Sir,

Thanks much.

The way I understand it, if I had no MAT correction--100% across the board--and I tuned her at 80 degrees, I should be lean when it's 40 degrees out, and rich when the car is fully warmed up and under boost, MAT 105ish. (My new Vibrant intercooler is amazingly efficient).

My problem is the values in the idle boxes of the VE Table that give me high 12s on a cold morning start give me 16s on a hot restart on a hot day. I have "Ignore MAT Correction at Startup" ON, and I need a very large number for the ASE Taper on a hot restart so that the MAT Correction for temps under boost (as you stated) doesn't pull fuel at idle, and I have it flat 100% at colder temps so it doesn't add even more fuel when cold. I read a post that explained when using some of the new large injectors on a small motor, the electrical properties of the injectors can be different enough at 40 degrees vice 200+ and that's what's happening to the AFR, not heat soak of the MAT sensor. Unfortunately, I can't find the post.

Poscat given, as well.

I have never seen, let alone touched that table. I found the explanation for this in the manual. However, I still have questions. If WUE is zero (100%) at high temps, does this table do anything? Does it do anything outside of WUE Analyze?

From the manual:
AFR Temperature Adjustment to Lambda - For most less radical engines targeting your standard stoich AFR is desireable. However, for various reasons you may want the engine to run more or less rich during warmup. Adjusting this curve allows you to raise or lower the target AFR during warmup. By Adjusting the curve down, the target AFR for that temperature will be lowered. For example if your target AFR at 32 degrees is 14.7:1 under normal condition and this table is set at -0.5, WUE Analyze will use 14.2:1 as the target AFR.

Have you made adjustments to yours?

Thanks!

Working on this today. I am confused by the idle advance settings. If the idle advance is off (which it is) then I am not understanding what is causing the idle correction giving the large 15* swing. Been reading and searching online but so much of what's out there is out of date or unresolved threads.

I did look again. When the 15* swing occurred, it was after the engine almost died and went out of CLI. At about 25 seconds on you Hot Restart Log. Otherwise, the swing is about 10 degrees, which is the sum of the engine going from 900 RPM at 40 kPa and 1200RPM at 30kPa. That is a 6* swing. Sorry to have misled.

@curly I presume that is just to have targets set to accentuate the creation of the WUE curve. After the fact, if EGO is on, would it not over-ride the offsets that were used, and drive the fueling back to the AFR Targets? Thinking it is this way as it is a VEAL functionality.

No worries at all. I'm just trying to understand things correctly and appreciate the help.

Yes, I target 14.5 at warm idle, I'm not in front of my tuning laptop right now, but my curve would roughly be -2.0 at less than 100 degrees. I'm also 100% ok with seeing afrs in the 10s very briefly if I start driving when cold. A lot of people freak out at the numbers on the gauge vs. how the car behaves I've found. I'm glad OEM's have found a way to warm up, let you drive immediately, never go below ~13 afr, and have zero hot restart issues, I haven't figured out the magic combo to do all of that.

My key is mid to low 12s during warm up, long ASE taper at higher temps, and an exponential growth looking AE curve.

Scott, I can start a new thread if you'd like, but this all seems related...

Curly, can I adjust the AFR Temperature Adjustment Curve to target say 13.5 at 220 degrees and then run the Warmup Enrichment Wizard under Tune Analyze Live during a hot restart and have it compensate for the heat soak? I plan to try that out, but right now my car is in the garage on jack stands.

Thanks,

No, it's fine. More info the better.

Made some progress this morning. Let the car get up to 180F which is when WUE ends. Let it sit for about 20 minutes and the coolant was around 160F. Adjusted the ASE more aggressively over 120F and extended the ASE Taper time from 120F and up. My taper curve is more U shaped now. Car started much better. Maybe a second or two lean and then it dropped back into 13-14 AFR. Waited for the car to cool to about 140F. Started right up, no stumble and the AFR was immediately in the low 14s. Let the car get back up to temp, 180F, and then waited 10 minutes. Coolant was 165F. Started right up. Again it went lean for a second or two then then went to about 14 AFR. Looks like I need to maybe add a tiny bit more of fuel in the 160-170F range but as it is now it's way better than when I first posted about it. I'll have to clean up my ASE curve and then re-do the WUE but that's easy enough.

So, decent day. I went out and drove the car for an hour. I knew heat soak from driving for an hour would be a lot higher than just idling in the garage. When I got home I let the car sit outside and after 10-15 minutes when I tried to start it, it was stumbling again. Tweaked the ASE and ASE Taper some more and got it to a point where it is just stumbling for a few moments but then levels out and the AFR goes back into the 13-14s. If I just started driving the car right away it would really be a non-issue. Much more livable than it was but I'll probably try to keeping tweaking this some more. May just be heat soak from the fuel rail and IAT combined? The IAT will move into the intercooler outlet in front of the radiator so that should help reduce the IAT heat soak. Not much I can do about the fuel rail heat soaking though.

I believe (and my experimentation supports) that this is a result of the injectors (and to a lesser extent the rail) heating up. Touch an injector right after you have been running for a long time and everything is heat soaked ... not hot. Touch the IM, or any other piece of metal around there, hot. Let the car sit for 10 minutes (off) after the heat soak, touch the injector ... HOT. Fuel cools injectors, a lot. When the fuel isn't flowing, they get hot like everything else. MAT does not fix this, Curly is all over it with his suggestion.

You want worst case? Like you mentioned up there, run to heat soak, then turn the engine off for like 5-10 minutes.

For reference, those AFRs almost perfectly mimic the cold AFRs of the stock ECU (on my 99 at least, and cant say what the coolant temps are since I dont have a way to read that)


But yeah, stock ECU pretty much goes to 11/12ish as soon as the WB warms up, then tapers up to the normal ~14.7 over maybe 5mins of idling (obviously depending on the coolant/air temps at the start)

Yes, all this started to happen after the Flow Force injectors went into the car and from what I've read in the past the smaller size of those injectors are more susceptible to heat soak than the OE injectors. Wonder if heat sinks (like on a computer CPU) attached to the fuel rail would help dissipate the heat faster? Anyone try wrapping to injectors or would it not matter since it's heat soaking hot gas from the inside?

I believe the hot lean restart is a complex problem: IAT sensor + fuel temperature + injector heat soak(?).

1. We can almost eleminate the IAT sensor heat soak moving it to the front part of IC cold side.

2. MS has a built in fueling correction table based on a fuel temperature. But it requires a temp sensor in the fuel rail.
Below is a data from ID entered in that table.

3. I will measure an injector opening time related to a injector temperature on next weeked. I am running an injector service business and have a required equipment.
https://cimg9.ibsrv.net/gimg/www.mia...f13c3708e5.jpg

That would probably solve a lot of issues. May be worth installing a sensor in the rail just to get this feature to work... May have to look into it.

The continental flex fuel sensors output fuel temp as well - this is what I'm using. Goes over the same wire too, super useful.

I believe fuel temp correction is intended to compensate for the dependence of fuel density on temperature.

Beer and tuning don't necessarily go together...

I attempted what's in quotes above. I got her good and warm and let her sit for 10 minutes. I queued up the warmup enrichment autotune and started her up. CLT was 206 and MAT 139ish. It was below 80 ambient. The autotune thingy didn't do anything. I went into "Gauge and Settings Limits" and set "Allow WUE Below 100% (only for LPG)" to "Yes". I let the car sit for a while and tried it again. I had completely overlooked that as soon as the car started it would start to cool down. Time on the log was moving right and the curve had more enrichment (my initial guess) with hotter temps, but as it cooled down it wanted to move left along the curve. I believe I almost caused the MS to have an embolism. That said, warmup enrichment autotune DID activate. It attempted to richen up the heat soak, but also extrapolated the curve backwards so I had a million percent enrichment at 30 degrees. It also changed the rightmost box to 100%, even though I had 117% in there as a guess. I was going to change the curve to something like 30, 40, ..., 190, 210, 230, 231, 250 and set that last box at 100%, but the rain picked up and was blowing into the garage. I called it a day.

Is this worth pursuing?

No

Edit: use ASE

Tuning and beer...

Hey guys I would like to bump this thread, I’m running a BP05, Wallbro 255, 60psi return rail w recent addition of Flowforce 640’s. I run MSPNP, MX3 chassis but same issues.. The injector upgrade was part of a DIY package upgrade ending in the installation of the smaller machined pulley That will push my M 62 up to factory limits or about 1500 RPM at redline. Currently i push about seven psi and the stock injectors were fine but I have a feeling they’re going to max out by the time I get to 11 or 12. I actually experienced a mild version of the hot start issues with the stock injectors running lean to about 16 but rarely stalling. I moved my IAT to the intercooler. Tuning has gone surprisingly smoothly for me to this point but this hot start issue with these 640s is really starting to frustrate me. I have been all over several threads and I can make the issue better with aggressive ego control But the car may still stall. Anybody else had any breakthroughs with this issue? How did you solve it? I’ve been all over this for weeks now it’s driving me nuts LOL

Which version of the MSPNP?

Post 33 above. After you answer Sixshooter, I may be able to help.

MM 9495 ms2

Same TB/TPS/ IAC as 95 Miata.. Only major difference would be the cam dizzy vs wasted spark but I doubt that is relevant. She runs smooth under load, 640’s improved every condition but hot restart. After a few minutes coolant about 213, MAT 108, Not too far off of regular running range in Tennessee summer. MAT may hit 120, coolant steady around 200 usually. City driving tends to raise intake temps more than hard pulls, decent no name intercooler under moderate boost

I'm not familiar with what is possible with MS2. Please post a Tune and I can open it and see what MS3 things will port over.

That is a good idea. My Saab 9-3 ‘daily’ overheated today (lol I’m an automotive masochist) soon as I get a minute I’ll upload that tune. Feel like I’m ‘fighting myself’ somewhere..

I got mine much better from when I posted. The IAT was moved to the intercooler pipe in front of the radiator and my ASE and Taper curves look like this. Not very elegant but I think the basic curve is similar to what others have done. It's not perfect but the car starts better and after 30 seconds of driving it's all good. Will continue to tweak it, just have not had much time after the charger was installed.

https://cimg5.ibsrv.net/gimg/www.mia...8742579f3c.jpg
https://cimg6.ibsrv.net/gimg/www.mia...f2892755ca.jpg

FWIW, I have a MSPNP2 (99-00 model) on a BP05, Walbro 290, non-return Radium rail. My GM IAT is in the outbound tank of the IC. I have experienced the hot-start problem (probably more so because of my non-return fuel rail), and I've gotten it to the point where hot restarts are tolerable...not perfect. Here are my ASE settings;
https://cimg5.ibsrv.net/gimg/www.mia...0f83913eff.png

ok here be my tune.. saab demanded my non work attention over last few days, so i haven't driven mx3 or 'prettied up' my tune since my last attempts at solving this issue on my own.. so here it is warts and all...

https://cimg7.ibsrv.net/gimg/www.mia...d503229039.jpg
Uh huh.. this is my current setting, I haven’t done any tuning since entering this thread.. seems like I’m going in the right direction, maybe no ‘majic bullet’ for the issue..

Good. OK. This is an MX3 with Kia Swap, If I understand correctly. MS2 PNP.

I'm not going to address simply hot re-starts because that is like discussing paint color of the living room of a house with a failing foundation. Tuning is iterative, but it still builds on some fundamentals; and trims from there.

1) A 1995 Miata comes with sequential injection. If your harness / engine is wired for sequential, that is what you should be running.
2) If you have 640 cc injectors, then the Req'd Fuel should be set up accordingly. Is this not a 1.8L engine?
3)WUE should be at 100% at around 185 - 190F. There is no reason to offset your entire curve to be offset by 5% at 205 CLT, which is normal operating temp.
4) These days, most people run "Incorporate AFR".
5) Don't set Flood clear at 100%. If your TPS calibration gets off, you won't get clear when you want it. Set it at 70%
6) On your VE Table, the area 35-90 kPa and 500-1100 is out of line with rest. Realize that the engine goes through that area immediately after starting. I tend to make 80-100kPa, low RPM a bit rich, rather than lean.
7) I cannot find where to set ASE as cycles or 0.1 seconds per cycle. It has been found to work well, with the times you show, when tenths of seconds is chosen.
8) I suggest using Idle Adaptive Advance Timing.
9) Your EGO should be set to PID, not Simple.
10) Go to Trubokitty.com and download the basemap for your Engine / Megasquirt. Look it over and get a feel for a good tune (but realize you will need to adjust for the injector size).
10) Your MAT corrections are not bad, though you should later tune that while running about 100kPa or higher. That is not an issue with your hot restarts, as you have set to ignore MAT corrections during ASE.

EDIT: Also check the “calibrations” of thermistors and AFR (wideband).
DNM

Knew this was coming.. lol Yup i started with a ‘B6D’ basemap.. runs okay But I need to back the trailer up before I pump the boost LOL. I will apply this logic and then re-post results, thank you for your reply

Actually that brings up an interesting point..Kia BP looks like MM95 motor, (besides mounts, water pump & ignition) but I’m using B6D harness. Timing looks good but should I run sequential injection on this motor? Sure I can figure the wiring out if necessary..

I don't know how well a motor runs with random injections on multi-port system. Seems like a waste to have multi-port and not run sequential, but I have no real experience there. Sequential vs wasted spark ignition is polish, but I envision sequential vs non for injection to be of value.

One other thing... Go to the Meet and Greet and join the community in a more formal manner. Then folks will know who you are, what you have, where you live (that can be put into your Profile to display beneath your Join Date).

Ok, they say ‘Knowledge without application is null and void’, so I applied ALL of the advice in DNMakison’s reply, with these results.
1. Hot start issue - without ego correction, leans to about 16/1 when ASE tapers off, but does not stall. I have idle VE at about 13.7. I consider this a success.
2. My fuel table was jaggy because of lazy base settings and VEAL tuning. Easy fix. Cross referenced Trubokitty & DIY maps
3. (The big one) sequential fuel injection. My car originally shipped with this feature, and so did the MSPNPMM9495. A simple software change made a world of difference in the running of my car. Smooth as silk and way more responsive. Naturally I had to do a general re-tune after making this adjustment. AE still needs a little tweaking but she has never run this well

I struggled for about 2 years with hot restarts, like you, on my '95 running an MS3. For the record, I also observed lean AFRs when the engine was hot.

Folks like DNMakinson, Curly, and Rev were very helpful but we couldn't really get it figured out. Playing with corrections of CLT, ASE, and MAT didn't make a lot of difference and I observed starting issues even when CLT was ~150*, which the MS wouldn't consider a hot restart. So that led me to investigate when else it could be.

Cutting to the chase, I found my problem was hot fuel, including vapor lock when really heat soaked. I figure the fuel gets heated as it sits in a hot rail, substantially lowering its density and therefore its energy for a given volume. Since the MS is operating on time (and therefore volume) the lower energy per volume of fuel was causing lean conditions. The problem was largely mitigated by adding a Conti flex fuel sensor and correcting fueling based on fuel temps. I called BP asking for fuel density values for the 10% ethanol blend sold by Arco here in Washington and calculated density changes based on temperature. I eventually discovered the engine wanted more fuel than the math predicted so I simply adjusted the curve based on observation.

I wondered why these hot restart problems would show up after installing an MS when I never had this trouble with the OEM ECU. I recall there's a little valve on the fuel rail that's invoked by the OEM ECU but is removed with a Megasquirt because it's considered no longer necessary. To be clear, I didn't completely investigate this path so I'm not sure if it's correct.

A couple of notes:

1. It's important to install the flex fuel sensor on the return line so it reads post-rail temps. My sensor is downline from the rail via ~2 feet of hose because that was the most convenient way to mount it. I need to move the sensor closer to the rail because it seems fuel cools a bit in the hose so the sensor is reading a bit cooler than what's actually in the rail. I suggest you mount the sensor as close to the fuel rail outlet as you can.
2. The Conti sensor takes ~30 seconds to accurately read temperatures once it's been turned on. When I first start everything, the sensor reads -30F even when the fuel is hot and will actually cause the MS to *remove* fuel instead of adding it. I've mitigated this somewhat by turning the key to On, waiting 30 seconds, and then starting the engine. This is only necessary when the engine is really heat soaked. I wonder if Conti has improved responsiveness of their sensor with a newer version...
3. I swapped out Flow Force 660s for ID1000s based on suggestions the injectors dead time behavior changes when they get hot. I found that didn't make a difference though. I contacted ID, Bosch, and an ECU engineer friend from a major car OEM. They all said heat technically causes a minor change but it's not enough to notice, and certainly not enough to account for hot restart issues. This led me down the fuel temp route.

My 97 equipped with FlowForce 640's and MS3 Pro also has hot restart issues. It's annoying, but not unbearable. My understanding is the PRC valve on the fuel rail references the fuel regulator to atmosphere, rather than manifold, for the first minute or so after a hot restart. I've played around with trying to mimic this concept with ASE, but wasn't successful. Part of my failure I attribute to not setting the taper time long enough while hot, but I'll save that for another day.. I can't imagine the heat soaked injector would be that big of an issue, especially when there isn't any real evidence (that I have seen) to support it. It's a nice theory, I just don't know if it's truly the cause.

Has anyone tried to utilize the PRC valve on a hot start, actually powering it through an aftermarket ECU? I believe this would take some custom wiring. Might be worth just pulling the line on the fuel regulator and referencing atmosphere with the manifold capped off, just to see if it actually helps with the issue. It should raise the fuel pressure at idle which would in theory be helpful. Another idea as a test would be running the fuel pump in test mode for a couple of minutes, hopefully bringing the rail temp down.