stumbling and choking after 5,000 rpm? - Page 3 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 01-12-2007, 01:00 PM   #41
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85psi ... it was stock alright!
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Old 01-12-2007, 01:03 PM   #42
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85psi ... it was stock alright!
Just trying to touch all bases
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Old 01-12-2007, 01:07 PM   #43
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You can't imagine how much help and advice you have given, I can say on behalf of the members here and espeically me the great appreication for you contribution. Sorry if I put that in a bad manner. I am just very fustrated and tire thinking the possbilites of it going sour!
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Old 01-12-2007, 01:17 PM   #44
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You NEED to get a fuel pressure gauge installed so you can see what is happening when you are in boost.

Or you could reverse the lines on the Vortech FPR and see what happens. I still think you are over fueling. After driving around in boost abit does the car smell like gas?
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Old 01-12-2007, 01:20 PM   #45
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yes.. in fact it does, I thought it was the little left overs gasoline when I installed the WalBro 2 days ago.
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Old 01-12-2007, 01:30 PM   #46
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Figured as much. You are probably dumping raw fuel out the tail pipe

When you changed to the walbro pump the problem got worse right, the stumbling came on earlier. Stronger pump builds pressure earlier, makes sense.

Using the 12:1 disc and the OEM pump you will max out pressure (85psi) at only 3psi of boost (in reality it is more like 70-80psi). As the boost climbs FP does not becasue the pump is flowing all it can. Now put in the Walbro and at 5psi you are getting 110psi of fuel. The 12:1 disc and the walbro are WAY WAY to much fuel, especially with the 1.8 injectors.

Why it did this with the OE fuel pump? Maybe you had a REALLY strong OEM pump and it was able to sustrain the higher pressure.

I bet if you could get a 6:1 disc you'd be in business providing the FPR you have now is working properly and is installed correctly.

Hope this helps.
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Old 01-12-2007, 01:39 PM   #47
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I'll let you guys know once I take the AFPR out... tomorrow! if that's the case, I will get a set of 305cc injectors and install my EMB. NO MORE AFPR! dammit!
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Old 01-12-2007, 01:41 PM   #48
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Get the problem sorted out and identified before you install the EMB. Adding in something else that is complex will just make matter worse if the car isn't running well before.
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Old 01-12-2007, 04:12 PM   #49
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Just buy another turbo miata and swap parts. Seriously, my car stumbles bad at the middle rpms under boost at WOT, but goes great past 5K. I just figure there is too much fuel to get used until the upper rpms. Shows what I know!? It would probably be a good idea to diagnosis this while the setup is simpler, but I am basically doing the same thing, just switching to MS. Just don't have the car out of the garage yet to get tuned by a friend. The screwy idle does tend to lend itself to a vaccum leak. Spray something in the engine compartment and watch it get sucked into the leak. Just watch what you spray.
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Old 01-12-2007, 04:22 PM   #50
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Did you go through the idle setting procedure after installing the turbo? Mine was way fucked and had to be fix initially. After that I still had to occasional idle droop, reset the idle speed again and haven't had anymore problems than I did when NA.
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Old 01-12-2007, 06:51 PM   #51
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im still heading more towards vacuum leak and not fueling. Overfueling in boost will not cause his idle issues. and if anything stumbling/hestiating is more of a lean issue.

And I still want you to check for fuel leaks damnit....takes 2 mins tops, dont need a gauge; just a paper clip and a wrench.
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Old 01-12-2007, 07:14 PM   #52
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You assume the idle issue is related.

Bullshit. When I was having the issue with a stumble right around 4000rpm it was from over fueling. If it was a vac leak why did the issue change and get worse when he added the Walbro fuel pump?
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Old 01-12-2007, 07:43 PM   #53
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I've run a complete weekend on the track running 9:1 AFR and 170rwhp (I dynoed the day before)....no bogging/hesitation/choking, just less torque.




It might end up being a fuel issue, but I dont think overfueling is the answer. Cause now with 115psi and the same thing, not worse, then i'd rule it out.

other things id consider: coilpack, wires & plugs, afm.
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Old 01-12-2007, 09:53 PM   #54
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Brainack, I went out yesturday and clamp the shxt out of the line. for minutes I still couldn't find anything.
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Old 01-12-2007, 10:00 PM   #55
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Quote:
Originally Posted by braineack View Post
I've run a complete weekend on the track running 9:1 AFR and 170rwhp (I dynoed the day before)....no bogging/hesitation/choking, just less torque.




It might end up being a fuel issue, but I dont think overfueling is the answer. Cause now with 115psi and the same thing, not worse, then i'd rule it out.

other things id consider: coilpack, wires & plugs, afm.
If could be how the fuel is being delivered and not necessarily how much. Although the quantity would certainly make a difference.

If it was a coil pack why does he see the problem at WOT (building boost) and not at 1/2 throttle (no boost)? Same with plugs? Wires? Afm? Not talking about a large amount of boost.

It looks to be boost related, and the one thing that is directly refrencing boost is the Vortech unit. Now a vacuum leak might show up at higher boost levels for sure, but it sounds like he's having the problem right at cross over to positive manifold pressure. Just went the FPR starts to clamp down on the return.

Car was fine (I assume) NA. So what did he change? A turbo (duh) and a whack load of extra fuel.

I'm not being argumentitive, I just don't want to poor bastard to go and replace plugs/wires/coils only to find out the FPR is label backwards or some ****.

Start with the basics, confirm what you've changed.
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Old 01-12-2007, 10:01 PM   #56
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Jayc, I went out yesturday and clamp the shxt out of the line. for minutes I still couldn't find anything.
I don't follow. What do you mean?
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Old 01-12-2007, 11:15 PM   #57
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Jayc, sorry... that was to answer Brainack.

Brainack, I just took out the AFM for a clean up and see if the brushes have good contacts.

I am still running with the linear AFPR, took out the vortech. I have not put in a fuel guage yet. might do it later today.

Let say I do not attach a vaccum line to the AFPR, will that disable its function?
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Old 01-13-2007, 12:55 AM   #58
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It should. What AFPR is it? Dude you have to get a gauge on there ASAP, messing around with out some information about FP is almost pointless and absolutely going to be frustrating.
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Old 01-13-2007, 09:19 AM   #59
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If it was a coil pack why does he see the problem at WOT (building boost) and not at 1/2 throttle (no boost)? Same with plugs? Wires? Afm? Not talking about a large amount of boost.
If any of those components has a problem, it'll be exacerbated when under boost.
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Old 01-13-2007, 11:00 AM   #60
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Well then I guess the thing to do is throw a couple of hundred bux worth of parts at it.
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