Help-Just when I thought I had it fixed!

[Mustang 1]

I have been working on my car alot! I had fuel pressure problems.Fixed that.Car ran well.Still had an occasional code 42.Could restart and went away.The only problem was at higher boost level the car would cut out.I suspected the coil pack so I replaced it today.The car ran great!Idled smoother,Ran smoother,and seemed to build boost quicker.On the way home a marveled at how well it ran!Then it happened...I was cruising at like 70mph and pressed the throttle about 3/4 down.The turbo whistled and spooled quickly,pulling hard,and then BOOM..A loud backfire out the exhaust and then a pop in the intake.A puff of smoke came out the exhaust when it backfired.The car ran smooth the rest of the way home unless you gave it any throttle-then it would pop and jerk.When I got home I thought maybe that I blew an intercooler hose off but they looked ok.I hooked up the otc scanner and the only thing that I thought looked funny was the IAC was sitting on 00.As you revede the motor,even under load standing on the brake it would only go up to like 50.Would this be right?Also after arriving home the car would idle smooth for a little while,from a few seconds to a few minutes and the die.Something else,in park or neutrel if you rev the motor and take your foot off the gas it will die virtually every time.The turbo is a PTE52 with less than 5000 miles.Any ideas?Also the tp voltage seemed kinda slow.like 42-44 at idle 4.5 at wide open,but seems to be slow.Another thing-with the key on and the car not running the IAC showewd 150,but 00 at idle,only like 50 at near wide open.Please help!

 

[gmgearhead]

sent you a pm

 

[Mustang 1]

This is so frustrating! I felt like the car was finally running as it should just prior to this happening. The plugs are new with like 200 miles or less and they are ac-delco.The first thought that I had was that an intercooler hose had came off or the vacume line at the turbo.The car idles smooth while it runs and I don't hear a vacume leak.It also runs smooth at low load like very little throttle.Just misses,backfires through the exhaust and backfires a little when you try to build up boost.It does seem that the tp voltage is lazy-like ya gotta push the throttle over half way to get the voltage to move and at wot it takes a second or two to reach 4.5.....When it backfired I was at 15psi of boost and the backfire was pretty sharp and I saw a puff of smoke that looked the color of rust.The weird thing is you can manipulate the throttle while driving by pushing it and sometimes it bucks and backfires and sometimes it won't-unless you push for alot of boost.Would a dirty throttle body,faulty IAC,or tps cause any of this?I have a very slight exhaust leak on the drivers side header-would this cause or contribute? Most likely cause of the backfire out the exhaust at highway speed with 15psi of boost?Just after putting on a new coil pack-within 15 miles..Good the coil pack have went bad or maybe ignition control module?Within the last few weeks new Walbro 340,new billett fuel pressure regulator,new fuel pressure gauge.All of this was because the gauge was reading 20 psi at idle when I actually had 65! I also put new ac plugs,new K & N filter,and now the coil pack.After the backfire this car runs worse than it ever has.The car ran better just prior to the backfire.I have an OTC 2000 so I checked every mode and the only things that seemed out of wack were the IAC at 0 at idea and 50 at WOT.Would this or could this cause any problems at idle?Also for weeks prior the car would die if you reved it in park and released the throttle and if you got in the throttle and built boost and took your foot of the gas it would die.The other reading that seemed weird was the travel of the throttle seemed excessive and out of wack to the tp voltage..seemed choppy and slow.Could this cause the problem.No knock seem period on the scan tool.Just prior to changing the coil I was getting a code 42 at times.But not tonight.All help is appreciated.

 

[Mustang 1]

Also,If I had a vacume leak wouldn't it miss at idle and light throttle?The possibility of a mechanical problems does exist,although I hope that is not the case.It would be my luck!

 

[gn85]

Do you have O2 readings??

When these backfires were occuring, did you happen to get O2 readings?? You said there is a possibility of a vacuum leak. I'm also wondering if your fuel pressure is changing as it should. You said that you had problems before with fuel pressure and such before. I'm wondering if your fuel pressure is keeping up and is indeed raising with the boost. Do you have a way of checking the fuel pressure at boost?

I'm not sure what to tell you about your IAC, although that may also be a leanout culprit.

Lastly, did you check this out to explain your code 42.

http://www.gnttype.org/maint/malf.html#42

Sorry, if I'm telling you things you already know.

HTH

 

[VIN7]

Bill,

The backfire at higher boost levels still leads me to coil pack/ign module problem. Since you have replaced the coil pack, I would suspect the ign module especially with a code 42.

Mike

 

[scgnx]

Are you using a LT-1 MAF w/ Tans+ ?

 

[Mustang 1]

Good Morning! Thanks for all your replies! I got up at 6:00 am and starting checking! The hunch about the vacume leak was correct in causing the 00 reading on the IAC. I puledd and check all intercooler hoses and vacume lines. I pulled the IAC to clean and with just the weight of the large crescent wrench it turned! I pulled it and cleaned it and reinstalled and got much better readings and te idle problems went away.Unfortuneately the backfire is still there. The backfire did not even exist before the coil replacement so I am exchanging the coil pack this morning and installing a new ignition module. What is the cause of a backfire out the exhaust? I know this seems like a dumb question. Is it unburned fuel and this leans towards an ignition problem? I really like my car but this is getting frustrating...Thanks again!

 

[V6 Beast]

After starting the car unplug the cam sensor and see if the problem goes away. The car will not start with it unplugged so be sure it is running first.

Steve

 

[Mustang 1]

A continuation of what I have done so far today! I replaced te ignition control module and the coil.This morning I removed and cleaned the IAC and found at that it was loose;hence the vacume leak and the 00 reading on the scanner.After I drove the car with the new parts installed it did not seem to backfire like it did before,but It still acted up,like a stutter at anything even approaching 12psi or higher.I then adjusted the IAC because after cleaning and tightening the IAC was still reading like 10 at idle.I turned the screw conterclockwise until I reached 25.Then I checked theTP sensor volts and they now were off.The reading was like .20 at idle and 4.0 at WOT. The best that I could come up with was .46 at idle and 4.86 at WOT. The car idles well and seems to run well,it seems to be smoother.I have not been over 10psi of boost since these changes since if it is stll messed up it will ruin my day.Could the IAC and the TP being out of wack cause the backfire? I hope so.I did notice something that might be strange.With the OTC 2000 on mode 51 it is supposed to show the spark advance.If it is working right the car has no advance!No reading whatsoever!Is that even possible?Would the advance be controled by the chip or ECM,or by the EST (ESC) module? Just in case I ordered a new EST module and will put it on tommorrow.Everyting else is new so what the heck!The part # of the module in the GM parts book says "knock Sensor"...Would this item only retard timing upon knock or does it also advance?I might even get a new ECM just to complete the package.Hopefully if everything is new as far as the fuel system,ignition system,and all sensors,maybe she will run right.All responses are greatly appreciated!

 

[MSDGN]

If it doesn't resolve the problem I would look at fuel pressure keeping up with boost as someone suggested...hook up a fuel pressure guage...tape it to windshield and watch what happens under boost...just went throught this with a friend...backfire under boost as it approached 16-17 PSI...checked out a bunch of things...coil pack/module...plugs...wires etc and everything checked out OK...didn't think about the fuel pump because he said it was pretty new but I've learned that new doesn't mean squat...it can still be bad...hooked up a fuel guage and there's the problem...under boost the pressure shot up at first and then started dropping rapidly...replaced the pump...backfire gone...

 

[Mustang 1]

Thanks for your replies.The fuel system has been checked and is functioning properly. Originally I had been loosing fuel prssure when I turned off the car.It was a bad check valve.I then replaced the fuel pressure because the fuel pressure seemed to go down when the car was hot. Then the car ran really bad.I then replaced the gauge with a remote gauge and I was overfueling.I had 65 psi at idle.After replacing the listed parts yesterday and adjusting the IAC and TPS the car idled better than ever and ran very well up to a point. No backfire,just a high load or rpm miss.Felt like a bad wire or wires.They are Taylor Race wires that are 2 years or more old .They ohmed out ok but 2 wires on the back of the coil and 1 at the front are rusted inside the wire!I ordered a new set that will be here today.Would the rust in the wire cause excessive resistance under higher load conditions.I kind of think so and hope so.If this is not the cause the only things on the car that are not new are the ECM,cam sensor,crank sensor.Every vacume line,every fuel line,fuel pump,fp regulator,gauge,plugs,tp sensor,0-2,IAC,coil,ignition module,EST module,fuel filter,and today the plug wires.I do still have the original MAF that seems tobe functioning properly.Although it is maxed out a 255..Could us a translator and extende.Just want to get it running at its bes with the current combo.I will keep you updated.

 

[gn85]

That definately could be a problem with the rust on the spark plug wires and your miss. You have to remember that the spark plugs are having a hard enough time making a spark when under boost. They need all the juice they can get and trying to make their way through a rusty connection doesn't help matters.

It sounds like you have/had several contributing factors to your problems. Since you've changed so much, remember to have your basics really covered. Doing all these repairs/replacements makes it easy to overlook things.

Glad to hear your seeing improvement though.

 

[Mustang 1]

It is just me again with a Turbo Buick update! I have always said that anyone with auto repair experience will seemingly almost always look for something more complicated than it is! Almost all of the fuel system repairs were because of an out of wack fuel pressure gauge.I thought that I had too little fuel pressure when I really had too much.Gauge reading 40-45psi low at times!At least I upgraded to a Walbro 340 from a 307.Now after all the sensor and electronics parts replaced I end up seemingly fixing it with a set of AC-Delco factory wires! I assumed that since the Taylor 409 Race wires ohmed o.k. and they were not very old they also were ok.They seemed to be the cause of the high rpm miss! I will not say it is fixed as I do not want to be let down yet again..But the performance has definitely improved.I will updat later....P.S.-Are these cars ever really finished?Ha-Ha......

 

[turbofrank]

For me everyday is test and tune.

 

[VIN7]

Whew,

I know what you mean about throwing parts at a car to fix a simple problem

I hope this is what fixes the loss of spark issues. I swap plug wires (Red's $24) each year, cheap insurance for sure.

Right now I am doing some abestos consulting work at the Kingston Power Plant and I am working during the night shift, but when this project ends we'll have to get together and check your tune and get to one of the tracks.

Mike

 

[Mustang 1]

Thanks Mike!Just call me any time. I believe you have my numbers.I would like to go to the track again.Back in October of 2002 my trap speed in the 1/8th mile was 95.89 mile per hour with the stock converter,the v-4 i.c.,different chip,before dragsprings and shocks,and other changes.Should run better now.I will probably go to the dyno first.See you later!

 

[gmgearhead]

put ac delco plugs in it and gap .030-.035 and you should be set to run with the best of them

 

[Intercooler]

So was it just wires?

 

[Mustang 1]

I talked to Mike latter tat weekend and it was the wires that caused his car to perform badly at the track that day, and theheat and humidity. My assuming the wires were good on mine caused me to replace lots of parts. Can you say "spares"!