When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I am dealing with heat soak on the fuel rail/injectors on my Turbo 1.8 1992 Miata.
I am running a SpeedyEFI and EV14 700cc Bosch PnP Injectors.
After spending many hours dialing in the hot/cold startups during the winter months, I am now dealing with heat soaking on the injectors.
I have set the ASE fairly aggressively at operating temps to increase enrichment for a longer duration as well as increase the crank to run taper time to 5 sec.
This does work but does have some side effects.
Engine will rev up to 2000 rpm for a couple of seconds when cold and if I restart the engine when hot immediately then will be rich for a minute.
I suppose these things are not terrible but not ideal.
I have read numerous threads on this fairly common issue and a few things caught my attention.
I see hondata sells a phenolic gasket that could lower intake manifold temps.
I am running a 190 thermostat and thought maybe a lower thermostat could have some positive effects?
I wonder would wrapping the fuel rail in heat tape help?
I also wonder do other ECU's have a better way of managing this.
I suspect the stock ECU was much smarter and the stock injectors were much smaller so was likely less of an issue.
I bump my idle valve duty cycle up as the coolant temp rises.
It's a band-aid for the cheap RX-8 Yellow injectors which have terrible low pulse width control (which gets even worse when they heat soak)/
I bump my idle valve duty cycle up as the coolant temp rises.
It's a band-aid for the cheap RX-8 Yellow injectors which have terrible low pulse width control (which gets even worse when they heat soak)/
My issue is with regards to heat soak is on startup.
When car is at operating temperature and then sits for a short period of time.
My car is running SpeedyEFI with stock injectors and I have a similar issue. It hasn't gotten too hot here yet, but I assume it will only get worse as we get into summer.
I assume the car is running lean on restarts? I didn't see any real symptoms in your post.
I've adjusted my ASE as well which is working well enough for now. I'd be interested to see your ASE table.
I assume you could adjust the cranking IAC duty cycle and cranking fuel to try to smooth out the high RPMs on cold starts, but I know that retuning that can be annoying as well.
Sorry if that isn't super helpful, but maybe it'll at least further the discussion.
Thanks for the response.
I have another thread in here where I had a conversation with another user regarding start-up's.
I was testing the Speedyefi on my stock 1.6 in that thread.
As my first time dealing with an aftermarket ECU the start-up was a pain and I never really got it dialed in before I pulled the engine.
I then installed the 1.8 with the turbo and larger injectors and paid DCwerx to remote-tune my car.
I do recommend having a tuner with all the experience to tune the car. Just safer this way.
But even after doing this and having about 7 revisions for the start-up I still was not satisfied.
So I started playing around with the start-up settings and trying to learn what the car wanted.
I had learned previously that the Miata likes those larger IAC cranking values for start-ups.
I always felt the car was too rich when starting and even when lowering the cranking enrichment values it did not seem to help.
So more air and less fuel.
For my larger injectors, I needed to lower the priming pulse-width and then fine-tune with the cranking enrichment.
For me, once it started it was ok and would idle fine.
I did play around with the ASE as well while watching the AFR's
Keep in mind the VE table needs to be dialed in well first.
So this went on for a couple of months during the winter after I finished my build.
I had it starting pretty well both hot and cold.
Once spring arrived I was out test driving while it was cold and refined my start-ups.
Then the warmer weather started to come and that is when I realized I was having some heat soak issues on my injectors.
If the car was hot and I stopped to get gas the car struggled to start afterward.
If I started it right away when hot it was fine because the cold fuel was keeping the injectors cool.
If I let it sit for 10 minutes I would get that vapor lock scenario and would struggle to start.
With stock or smaller injectors, this would be less of an issue or even non-existent.
For stock injectors, you would likely not need this high enrichment and duration at operating temperature with the ASE.
Find attached a couple of tune files.
One is my tune before tuning for boost and before adjusting for heat soak.
The other is my tune for about 13psi of boost with adjustments for heat soak.
Again for the heat soak the ASE has added enrichment with a longer duration when hot and a longer crank to run taper in the idle settings.
This for my 1.8 with the EV14 700cc injectors.
I am still playing around with the ASE but it does work pretty decent.
I noticed you said your car struggles to start, not to idle. I might have been confusing my issue with yours. My car will idle very lean in the scenario you explained, but still starts pretty easily.
I'm interested in looking at your tune. I'll try to do that sometime today or tomorrow.
That was a good catch and diode fix for your issue.
I did not have that problem. I think I have normal IAC values when idling rather I am using larger ones when cranking. I recall my IAC being at 31 give or take
I don't take any credit for the tune files uploaded as these were done by Dwight over at Dcwerx. I did however spend alot of time on the startup events.
I am not a tuner so can't really help with your issue as I know there can be a few variables. I guess adding a bit more fuel to the idle range of your VE table dues not help? The AFR table is set to 14.2 ish in the idle range?
Target AFR is checked? Idle is being set when at operating temp? You can play around later with the cold range with your ASE and WUE. That's all this noob has got to give.
I would highly recommend talking with Dwight over at Dcwerx if you can't figure it out. He is super friendly and knows these speeduino's and Miata's very well. He spent 30 min on the base tune before we even turned the key. One hour later I was driving around.
Sorry if I wasn't clear. I'm pretty sure I just need to add more ASE but haven't gotten around to fine tuning it yet.
I autocrossed on that tune this weekend and for the most part didn't have issues. A few moments of rough ( lean ) idling when turning the car off/on in grid, but overall everything went smoothly.
I've got DCWerx on my list for tuning after I get my turbo installed.
Didn't mean to hijack the thread, sorry about that.
I have read other issues with running RX8 injectors especially if they are clones. If you only lean when hot for the first 10 sec or so then yes the ASE will fix that. Just add 10-20% more to that temp range and see what AFR you get. Then you can just scale it from cold to hot.
No worries on adding to the thread, hopefully others can use our information.
Another remote tuner that is well reviewed and has done a ton of Miata's with the speeduino is Steve Hanegev... Steve's Remote Tuning.
I am in a similar boat as you are. 90 Miata MS3Pro, FF640cc injectors, FM Rail, turbocharged.
I see heat soak issues after numerous hot restarts that seem to work towards being more lean the longer it's driven after multiple hot restarts.
For example if I drove the car from cold to hot continuously for 3-4 hours without stopping it's good. Fire it back up after a few minutes it's still good. If I drive short distances from A-B-C-D with a few starts in between then I can see AFRs begin leaning out during cruising only.
Now I've tried to isolate the concern. Disabled EGO control, no AFR correction, set all MAT values to 100 so no correction there. Seems a little better so maybe I need to work on the actual fuel table? It drives great and has rock solid AFRs until those multiple hot restarts. I also noticed a difference in my wideband gauge (AEM 30-4110) and what TS is showing sometimes by .3-1.5
Also randomly the TPS will be good but then randomly spike negative. I have checked all connections, calibrated it a few times but it only happens after heat soak.
Correlation is not exactly causation but it seems to me that the heat soak is why. So if anyone has had similar issues or suggestions of what to check I'm all ears.
My understanding of heat soak is only for start-up. Once the car is running again the cool fuel from the tank cools the injectors and all is well. I am now going to monitor the AFR a little more closely for this situation you describe.
If your AFR guage doesn't match TS I think it can be corrected on TS. If the values are only offf when hot this would be odd. Is your AFR signal ground , grounded at the ECU ground ? I ran mine into the engine bay and attached where the wire loom bolts to the block.
Did you inspect clean all ground points?
Tuning at operating temp for sure.
Some injectors are better than others? I wonder.
After market rail? Do you also run an aftermarket fpr?
Just some thoughts .
I can say it's a learning curve for me like many others.
Dialing in startups is indeed difficult.
Speedyefi has a Facebook troubleshooting page that is littered with startup issues. Visit it for more help and advice. The guys over at Speedyefi are always offering advice.
For me I am still dialing in the startups but am getting very close. I thought I had it nailed until I realized I had to tune for the heat soak issue. This changed things and maybe for the better. I was using larger IAC cranking values and it would start well but now that I am using a longer crank to run taper at 5 seconds. I have been bringing the IAC cranking values back down to normal 40-65 type values and it seems to be still starting well and perhaps even better. The outdoor temperatures are warmer here now in Canada so this may have some effect. I don't drive the car in the winter months anyway, but this is when I was tuning it.
When I settle on a final tune, I will come back and post it for others to view.
Here is a modified tune with some lower IAC Cranking values and a possibly better ASE for dealing with heat soak.
Seems a bit better with less rev hang and smoother transitions for the IAC.
1.8 Turbo Miata. Kraken top Mount 2560R, EV14 700cc Bosch PnP Injectors, 3" Exhaust, 13psi
I have started another thread with a different issue regarding my tune.
In the event that someone is referencing my tune for their SpeedyEFI I have made some important changes.
I was getting misfires in boost with WOT going through the gears.
The changes that were recommended by the guys at Speedyefi were.
Injector Output to Paired.
Squirts per cycle to 2.
Trigger Filter to Weak.
This solved my misfires but changed my cold startup. I will need to revisit this.
I hated how this car started when cold and am hoping I will have better luck with these changes.
Here is my current map.
I will come back to repost when I have refined my startup...again
So with this misfire resolved I decided to start over with my start-up settings.
I know it's common to dump a bunch of fuel into the cranking enrichment but always felt it was flooding and in turn backfiring. So I previously had the best results with lower priming pulse and lower cranking enrichment.
This may have been because of the previous settings, but not sure.
Maybe it just needed even more fuel. It was close but I needed large IAC values and would rev hang a bit at 2000rpm when I bumped up the crank to run taper for the heat soak issue.
So I downloaded and was looking at an MS3 base tune posted at https://trubokitty.com/#/tune (Braineack)
I was surprised at how much fuel was used in cranking enrichment for the startup.
So I decided to take these values and insert them into my map.
With these settings, I had lower IAC cranking values and a ton more cranking enrichment, and I bumped my priming pulse backup.
I increased my crank to run taper to 6, and cranking advance angle to 10 deg.
My ASE and WUE seemed fine before so I did not make any changes there with maybe a bit more ASE. The ASE was well set up for heat soak so did not change that curve.
I haven't had a chance to do a true cold start but was surprised that the car seems to start fairly quickly. Maybe the COP's helped here but not sure.
I hope this is going to work when cold.
My question is what kind of AFR should I be seeing when the car first starts up, as well as what AFR when ASE is on and again when WUE is on? Am I still aiming for 14's?
I am guessing initially when it fires it will be rich due to the fuel added to start.
But when ASE is on what value here since I can control this fairly easily?
So now that I have reverted back to 2 squirts per engine cycle to solve the misfires in boost during wot I am now back to a rough idle when the engine is hot. Idles fine when cold but once warmed up it hunts a bit and the AFR's bounce around a bit. Fix one thing and another arises. I can tune out the idle issue by adding more fuel in the VE table. Then it will idle perfectly but the AFR is at 12.
Hey there. I was wondering if you solved your issue? I have a 99 Miata FMII with Hyrda ECU, 1000cc injectors and return style fuel system.
I have heat soak starting issues after running my car hard on hot days. For now, I solve my issue by parking on hills so that I can dump the clutch to get it going. Car runs great if I can get it started.
I have solved the issue. My last tuner told me there is no such thing as heat soak at the rail/injectors? There was certainly something happening when hot. I don't know anything about your tuning software but we used a longer crank to run taper. Around 10-12 seconds in tuner studio. I also added a bit more ASE when at 190F. If the engine has been running hard in boost and I try a hot restart it takes a second or two to settle but has been good since.
If you need some help with the tune look up Adam Peetz on Facebook. He is a pretty smart remote tuner.
Yeah, no one really has Hydra anymore. It makes everything a little more annoying when asking for advice. I did have flooding issues with the larger injectors awhile back, but I turned off the "Crank Multi Inject" feature. That feature made the injectors fire on every ignition. Now I let the fuel pump cycle 3 times before trying to start it. My fuel system doesn't hold pressure if the pump isn't running because it all leaks back into the tank. I don't have cycle the pump if the engine is hot.
Would if be possible for you to send a picture of what you adjusted?
I am really not the guy to ask for help. I am pretty new to all this. I would really suggest messaging Adam with your story. He is an old school tuner so may be able to help or offer some free advice. He is really big on helping out the community. Worth having a chat. Cheers J
04-17-2023, 10:41 AM
Dealing with Heat Soak
0
