'92 IROC 2.5 Turbo...engine cutting out?

[zer0321]

Okay so I have a '92 Daytona IROC...It has the 2.5L Turbo engine and A523 Manual Trans. The original engine went bad, so I replaced it with one from an '89 Lebaron. I did the timing belt and clutch while it was out since I already had it apart.

Anyways, It starts and sounds good, idles normally, revs fine in neutral, but I'm having problems with it cutting out violently under load, anything more than slight throttle and it starts bucking and cutting out. If i press the throttle more, it keeps doing the same thing...if I let go, it smoothes out at idle and will do the same thing once I try to accelerate again. (no boost gauge yet, but i'm assuming this is happening when it starts to build boost...I will be installing a gauge soon)

This whole process does not set off the check engine light or any stored codes...so far, I've tried replacing the fuel pump and filter because the original one was whining loudly, so I thought that may be it, but the only thing that changed was the loud whining went away. I started checking vacuum lines...haven't found anything yet.

Any ideas what the problem is here?

[NAJ]

Unfortunatly the symptoms by themselves will be difficult to diagnose online, you will have to run diagnostics to narrow down the problem.
I would start by being absolutly sure cam and ignition timing are correct.
Verify fuel pressure is correct, you will need to connect a gauge. 53-57 psi static pressure, you will lose 1 psi rail pressure for every 2"hg applied to the fpr running and add 1 psi rail pressure for each lb of boost.
Verify vacuum/pressure is correct to the baro solenoid and from the baro solenoid to the map sensor. Be sure map voltage matches vacuum pressure.
Check tps voltage and sweep tps looking for dead spots.
(voltage charts are located in a "sticky" under "voltage tables".)
Verify secondary ignition components are ok, plug condition, gap, insulators for cracks, arcing, open, high resistance in ignition wires including coil wire, dist cap for cracks, arcing coil.
(use a spray bottle of water to spray all components with the engine running, arcing will be visable or you will notice the engine start to stumble).
Perform a wiggle test on the underhood wiring and connectors with the engine running, this will help to isolate faulty connections, broken terminals in a connector etc.
Get that boost gauge hooked up or at least connect a vacuum/pressure gauge so you have an idea what the pressure is when the problem occurs.

[zer0321]

Quote:

Originally Posted by NAJ Unfortunatly the symptoms by themselves will be difficult to diagnose online, you will have to run diagnostics to narrow down the problem. I would start by being absolutly sure cam and ignition timing are correct. Verify fuel pressure is correct, you will need to connect a gauge. 53-57 psi static pressure, you will lose 1 psi rail pressure for every 2"hg applied to the fpr running and add 1 psi rail pressure for each lb of boost. Verify vacuum/pressure is correct to the baro solenoid and from the baro solenoid to the map sensor. Be sure map voltage matches vacuum pressure. Check tps voltage and sweep tps looking for dead spots. (voltage charts are located in a "sticky" under "voltage tables".) Verify secondary ignition components are ok, plug condition, gap, insulators for cracks, arcing, open, high resistance in ignition wires including coil wire, dist cap for cracks, arcing coil. (use a spray bottle of water to spray all components with the engine running, arcing will be visable or you will notice the engine start to stumble). Perform a wiggle test on the underhood wiring and connectors with the engine running, this will help to isolate faulty connections, broken terminals in a connector etc. Get that boost gauge hooked up or at least connect a vacuum/pressure gauge so you have an idea what the pressure is when the problem occurs.

Okay, so I got my boost guage connected up, looks like I have good vacuum...I redid all the lines because the plastic connectors kept breaking. I triple checked them all.

Checked all the electrical connectors and the TPS tested okay.

One thing I should point out is that this problem seems to be occuring as soon as the turbocharger starts to build boost, as soon as the boost gauge reads past 0, it seems to cut out.

This seems like a fuel pressure problem, because it has a hard time starting after sitting for awhile, it will take alot of cranking or priming of the pump to get it to start, and when it does it kind of gradually stumbles up to a normal idle and then is okay. I don't have access to a fuel pressure gauge yet, but until then could this be a fuel pressure regulator problem? the pump and fuel filter have already been replaced, the lines are not clogged. (still no codes!)

Thanks for the advice

[NAJ]

It could very well be a FPR problem but until fuel pressure is verified it is all a guess.

[joepar92]

im sorry that ur iroc engine screwed up

[zer0321]

Okay, I got the fuel pressure regulator installed. It seems to start easier now, but still needs more cranking than it should. I had my buddy come over with his fuel pressure gauge and check it out and he said it was fine.

I have noticed that the idle is a little bit higher than it should be, just over 1000rpms, maybe 1050rpms. It tries to idle lower but runs rough and goes right back up. There is a small bit of popping coming from the exhaust.

I've been poking around and thought this could be a timing issue, when I put my timing light on, I notice that everytime the exhaust pops, the timing jumps to the right a couple of notches (while looking at it from the drivers side) and then goes back to normal, its almost like if you were counting 1-2-3-4 on every 4th beat it will pop and the timing goes jumps a bit, even though the tach stays steady. I'm thinking it is missfiring a bit. I have new plug wires and cap/rotor, but the plugs are kind of old...

I'm thinking that I'm going to get some new spark plugs and double check the timing and see where that takes me, what do you all think?

[NAJ]

Popping thru the exhaust is due to incomplete combustion so checking the secondary ignition and chemically cleaning the fuel injectors is a good idea.
Sounds like it is related to 1 cylinder so it could also be something internal like a burnt valve, if correcting your basic ignition does not correct it you will need to run a cylinder leak down test to verify.

[zer0321]

Well, I got it all sorted out today. Thanks for all the help! It really made it easy to track this down. I think my old FPR was definetly bad because it was leaking fuel through the vacuum line!, Long story short, the old plugs were worn out, orange/rusty looking and the gap was about .075-.085 depending on the plug!

I got some new champion plugs today at autozone, gapped them to .035 and put them in, this thing takes off like a rocket now!, nice smooth idle- no more popping exhaust!