2003 PT GT Backfire on 93 tune

[4angels]

I have been reading a lot on this forum trying to answer my own question but to no avail. 3/4 to WOT it starts to backfire and cut.

Just loaded for the first time today, after updating the calid as instructed.

went back to stock tune and runs fine but hard to get it to go to 10PSI now. I would appreciate any instructions/input.

Car is stock except for VAK hard pipes and a Magnaflow muffler.

[duster360]

Backfire/cut caused by misfires caused by weak ignition that can't fire the plugs as well with a leaner A/F and higher boost.

Leaner A/Fs and higher cylinder pressures require more voltage to reliably create a spark. The 93 tune leans A/F from stock of ~10.5 to around 11.8-12.0 and also increases boost considerably. Once the ignition system start to gets worn, leaner mixtures at higher pressures are much harder to fire and often misfire(Backfire/cut).

The lower boost and richer A/F of the stock tune makes it appear to "fix" the misfires.

new plugs and wires are usually all it takes to fix it. Don't worry about the stock coil. its actually pretty stout.[/i]

[4angels]

Backfire/cut caused by misfires caused by weak ignition that can't fire the plugs as well with a leaner A/F and higher boost.

Leaner A/Fs and higher cylinder pressures require more voltage to reliably create a spark. The 93 tune leans A/F from stock of ~10.5 to around 11.8-12.0 and also increases boost considerably. Once the ignition system start to gets worn, leaner mixtures at higher pressures are much harder to fire and often misfire(Backfire/cut).

The lower boost and richer A/F of the stock tune makes it appear to "fix" the misfires.

new plugs and wires are usually all it takes to fix it. Don't worry about the stock coil. its actually pretty stout.[/i]

Thanks, already put in the new NGK's, waiting on the 8.5 wires....
Tired it all again and it seems that at 44-4500 rpm the boost spike to 20 and then cuts out and goes away all together. Rolled into it and no backfire just boost issue. From the line at WOT I have both problems.

What do you suggest on the boost issue? Not real drivable loosing boost at 4500 unless its just getting the groceries.

[duster360]

Backfire/cut caused by misfires caused by weak ignition that can't fire the plugs as well with a leaner A/F and higher boost.

Leaner A/Fs and higher cylinder pressures require more voltage to reliably create a spark. The 93 tune leans A/F from stock of ~10.5 to around 11.8-12.0 and also increases boost considerably. Once the ignition system start to gets worn, leaner mixtures at higher pressures are much harder to fire and often misfire(Backfire/cut).

The lower boost and richer A/F of the stock tune makes it appear to "fix" the misfires.

new plugs and wires are usually all it takes to fix it. Don't worry about the stock coil. its actually pretty stout.[/i]

Thanks, already put in the new NGK's, waiting on the 8.5 wires....
Tired it all again and it seems that at 44-4500 rpm the boost spike to 20 and then cuts out and goes away all together. Rolled into it and no backfire just boost issue. From the line at WOT I have both problems.

What do you suggest on the boost issue? Not real drivable loosing boost at 4500 unless its just getting the groceries.

I'd get the new wires on and retest the backfire/cut.

Not sure what you mean by "then cuts out and goes away all together" but it could be 2 things:

1) "goes away all together" The stock turbo will "lose" boost starting at around 4500. The normal 20psi spike will fall to 12-14psi by 6000rpm. I've attached a log showing what this looks like. Look at WOT at time :17-:19

2) "Cuts out" Might be an "overboost protection" If the PCM thinks your too far over a preset TIP sensor pressure, it will perform what most guys call a "boost cut", in which it momentarily(<.5s) cuts all power to the coil/injectors. It will be obvious on your log. The 93tune is suppose to raise this TIP sensor limit but maybe since you have a PT PCM its not quite right. idk.

[/b]

[4angels]

Backfire/cut caused by misfires caused by weak ignition that can't fire the plugs as well with a leaner A/F and higher boost.

Leaner A/Fs and higher cylinder pressures require more voltage to reliably create a spark. The 93 tune leans A/F from stock of ~10.5 to around 11.8-12.0 and also increases boost considerably. Once the ignition system start to gets worn, leaner mixtures at higher pressures are much harder to fire and often misfire(Backfire/cut).

The lower boost and richer A/F of the stock tune makes it appear to "fix" the misfires.

new plugs and wires are usually all it takes to fix it. Don't worry about the stock coil. its actually pretty stout.[/i]

Thanks, already put in the new NGK's, waiting on the 8.5 wires....
Tired it all again and it seems that at 44-4500 rpm the boost spike to 20 and then cuts out and goes away all together. Rolled into it and no backfire just boost issue. From the line at WOT I have both problems.

What do you suggest on the boost issue? Not real drivable loosing boost at 4500 unless its just getting the groceries.

I'd get the new wires on and retest the backfire/cut.

Not sure what you mean by "then cuts out and goes away all together" but it could be 2 things:

1) "goes away all together" The stock turbo will "lose" boost starting at around 4500. The normal 20psi spike will fall to 12-14psi by 6000rpm. I've attached a log showing what this looks like. Look at WOT at time :17-:19

2) "Cuts out" Might be an "overboost protection" If the PCM thinks your too far over a preset TIP sensor pressure, it will perform what most guys call a "boost cut", in which it momentarily(<.5s) cuts all power to the coil/injectors. It will be obvious on your log. The 93tune is suppose to raise this TIP sensor limit but maybe since you have a PT PCM its not quite right. idk.

[/b]

"goes away", what I mean here is the boost goes to zero. it sounds like the waste gate opens and allows all presure out and yes it does feel like I have lost spark. I tried to make a log but not sure I did it right and wouldn't know what to look for! If I could figure out how to put it here could someone look at it?

[duster360]

Thanks, already put in the new NGK's, waiting on the 8.5 wires....
Tired it all again and it seems that at 44-4500 rpm the boost spike to 20 and then cuts out and goes away all together. Rolled into it and no backfire just boost issue. From the line at WOT I have both problems.

What do you suggest on the boost issue? Not real drivable loosing boost at 4500 unless its just getting the groceries.

I'd get the new wires on and retest the backfire/cut.

Not sure what you mean by "then cuts out and goes away all together" but it could be 2 things:

1) "goes away all together" The stock turbo will "lose" boost starting at around 4500. The normal 20psi spike will fall to 12-14psi by 6000rpm. I've attached a log showing what this looks like. Look at WOT at time :17-:19

2) "Cuts out" Might be an "overboost protection" If the PCM thinks your too far over a preset TIP sensor pressure, it will perform what most guys call a "boost cut", in which it momentarily(<.5s) cuts all power to the coil/injectors. It will be obvious on your log. The 93tune is suppose to raise this TIP sensor limit but maybe since you have a PT PCM its not quite right. idk.

[/b]

"goes away", what I mean here is the boost goes to zero. it sounds like the waste gate opens and allows all presure out and yes it does feel like I have lost spark. I tried to make a log but not sure I did it right and wouldn't know what to look for! If I could figure out how to put it here could someone look at it?

If it makes alot of racket, then it sounds like a boost leak. The extra 5-6psi can blow hoses off unexpectedly

just log
MAP
RPM
BARO
MPH

save it to your desktop, then attach it to your next post using the "Add Attachment" window under the post dialog box

[4angels]

My log has a little more but I believe it covers what you mentioned. It was interesting to figure out how to log!

I got tied up in traffic so look between minutes 1 and 2 and then again between 3 and 4. That is where I got it to act up.

With regard to boost leak, all has been checked and looks tight. Under stock tune it is holding but I cahed the clamps just to be safe.

[duster360]

Somthing up with your TPS sensor or your Foot.

the PCM thinks that anything over a TPS voltage of 2.8v is WOT. ONLY at WOT will it maintain a stable boost. The PCM uses throttle posistion to judge how much torque is "desired" by the driver. If it doesn't see a WOT level TPS voltage it will open up the wastgate and boost will drop.

Your TPS volts are all over the place when it should be table flat at the times that "look" to me like WOT. Look at the log I posted to see what I mean. That guys TPS is high(3.8v) and flat at WOT.

Rarely is your TPS voltage over 2.8v and worse, EVERYTIME boost tanks its PROCEEDED by a drop in TPS voltage(time 4:20-4:22). So either you're getting off the gas at EXACTLY the same time you clain to be having the boost drop or your TPS sensor or wiring is fubared.

[4angels]

Somthing up with your TPS sensor or your Foot.

the PCM thinks that anything over a TPS voltage of 2.8v is WOT. ONLY at WOT will it maintain a stable boost. The PCM uses throttle posistion to judge how much torque is "desired" by the driver. If it doesn't see a WOT level TPS voltage it will open up the wastgate and boost will drop.

Your TPS volts are all over the place when it should be table flat at the times that "look" to me like WOT. Look at the log I posted to see what I mean. That guys TPS is high(3.8v) and flat at WOT.

Rarely is your TPS voltage over 2.8v and worse, EVERYTIME boost tanks its PROCEEDED by a drop in TPS voltage(time 4:20-4:22). So either you're getting off the gas at EXACTLY the same time you clain to be having the boost drop or your TPS sensor or wiring is fubared.

When the WG spills at 4k I am getting off the gas for fear of hurting the car. Should I try again on open road without traffic and log again? As i mentioned I was stuck in traffic, speed up, slow down for most of the log. the only times i could "run " it were the times I mentioned. Or, based on what you asid, I may want to get a new TPS and try again?

[mikel]

Have you ever altered or unplugged the TPS for any reason?

[4angels]

Have you ever altered or unplugged the TPS for any reason?

No, I am not even sure where it is? But I am not the original owner either.

[4angels]

I just found this. It seems this is a common problem with the SRT4. Unless there is something else I should check, I will look at this first and try again?

http://www.turbododge.com/forums/f11/f3 ... oblem.html

[mikel]

there you go...

[duster360]

I just found this. It seems this is a common problem with the SRT4. Unless there is something else I should check, I will look at this first and try again?

http://www.turbododge.com/forums/f11/f3 ... oblem.html

The SRT has more issues with the TPS wiring because the wiring is attached to the radiator core support and it gets strained due to engine torquing. The SRT hearness was just made a bit too short. With the PT TPS wiring and thottle body in completely different position its not a good comparison.

Thats not to say your TPS could still be an issue.

The PT TPS is on the Throttle body right on top of the enigne, on the end of the Intake manifold. The hose from the air cleaner is connected to it.

To test the TPS sensor and harness:

1) Key ON/Engine OFF; Log or display TPS voltage.
2) Slowly open the throttle. The voltage should smoothly increase from ~.7 to about 3.0-3.9v(exact value is not important) at full throttle. If the voltage drops off or is irratic the TPS sensor could be bad.
3) To test the wiring, hold the TPS at WOT(brick on gas pedal) and jiggle, shake and tug on the connector and harness. The voltage should remain constant. If the voltage drops off or is irratic, repair the connector/harness.

[4angels]

Thats not to say your TPS could still be an issue.

The PT TPS is on the Throttle body right on top of the enigne, on the end of the Intake manifold. The hose from the air cleaner is connected to it.

To test the TPS sensor and harness:

1) Key ON/Engine OFF; Log or display TPS voltage.
2) Slowly open the throttle. The voltage should smoothly increase from ~.7 to about 3.0-3.9v(exact value is not important) at full throttle. If the voltage drops off or is irratic the TPS sensor could be bad.
3) To test the wiring, hold the TPS at WOT(brick on gas pedal) and jiggle, shake and tug on the connector and harness. The voltage should remain constant. If the voltage drops off or is irratic, repair the connector/harness.[/quote]

Thanks, fortunately for me a long time friend owns a shop. I took it to him at noon today and he just called to say TPS is fine. Wiring is fine. He did find however that the small hard plastic line that reads the Air Intake Pressure had a crack. That is now fixed and would explain low boost.

It does not however, explain the spike and loss of power. He had told he that the normal course of action by the ECM when max boost is exceeded is to open the WG and shut down the injectors until boost is back to acceptable limits. If true in this case, it would explain my coment of loss of power and the WG dump.

So at this point I am not sure where to go next to figure this out?