Shitty acceleration - Dodge SRT Forum
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post #1 of 13 (permalink) Old 12-14-2016, 10:47 PM Thread Starter
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Shitty acceleration

I have a problem when I try to accelerate at full throttle, Letī say Iīm driving at 20 or 30 mph, then I floor the pedal to get full power, then the engine chokes like if its not having enough air or proper inition from the sparkplugs or feels like if I were trying to push an invisible obstacle because the acceleration is not as strong as is supposed to be. I used to have wheelspin on 1st and 2nd gears at full throttle but now the car accelerates erratically, and even overboosts and cuts ignition and/or the revolutions climb to approximately 3500- 4000 rpm and then stay there for as long I fully press the throttle while the acceleration sucks.

Letī say iī not able to challenge even a turbocharged kia.


I have an unmodified stage 3 w/toys, (pcm control, everything mopar) with 3 inch o2 housing and 3 inch catback, stock airbox with KN filter, vpower ngk sparkplugs, granatelli wires, etc.
I checked for vacuum line leaks (there are none), checked the turbocharger, worn sparkplugs, computer codes, etc. I couldnt find anything wrong. Apart from this problem the car runs fine when idle, driving or cruising or accelerating moderately. Fuel consumption is normal, not any other problems.

Another symptom is when I press the accelerator pedal from zero to to half travel, the acceleration is smooth and seems fine, but after half pedal travel specially if I press the pedal suddenly to the bottom, then the car behaves erratically, it will even overboost when on DAB 2 or 3 and cut ignition (DAB 1 keeps the boost at 15 psi), or it will try to accelerate but with a lack of a strong pull, like if the car were pulling a heavy trailer and the revs climb up but slowly or it will accelerate moderately fast but then behaves like there is an invisible limiter at around 4000 -5000 rpm and the revs get stuck there.

So short story, my stage 3 SRT-4 is not accelerating like it should I even avoid full throttle so I donīt have this kind of behavior.

The last thing I tried to diagnose is the TPS sensor, I measured the voltage from the sensor with a multimeter and it looked fine at full open throttle the voltage was like 4.7v and progressively moved as the throttle plate opens and closes.

I will try to make a video of this problem because is very hard to describe the car behavior thatī why the long explanation. I think I checked everything and ran out of ideas, thatī why I ask the forum for help to find the solution!


Greetings!

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Ralf

Dodge SRT-4 2004 Stage 3R Electric Blue
BMW 330i 2002

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post #2 of 13 (permalink) Old 12-15-2016, 08:06 AM
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Did you check the MAP sensor voltage?
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post #3 of 13 (permalink) Old 12-19-2016, 10:36 PM Thread Starter
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Originally Posted by goldfingerfif View Post
Did you check the MAP sensor voltage?
No, I didnīt. but I do not have any check engine codes. How can I check that this sensor is working right?

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post #4 of 13 (permalink) Old 12-20-2016, 07:24 AM
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MAP doesn't always throw an CEL. There's a couple different ways to check the MAP. Easiest would be to pull it and see if it's covered in dirt or oil or if you got an spare laying around just swap it. If you have a data logger like a Diablo Sport you check what pressure it says with the car on and with it off and see if it's reading correctly.
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post #5 of 13 (permalink) Old 12-24-2016, 09:26 AM Thread Starter
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Iīm thinking that maybe the catalytic converter must be clogged. I have a thermal exhaust with cat. Iīm going to restore it to the mopar performance exhaust without cat and check.

The thing that I donīt know why is happening is that I have oil in the WGA vacuum lines.

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post #6 of 13 (permalink) Old 12-27-2016, 07:29 AM
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A clogged CAT is a possibility. You said it's not going above 4-5K RPM and it's as if there's a rev limiter? If it still behaves strangely after eliminating the possibility of an clogged CAT, check your cam position sensor. I had a cam position sensor go out on my old 2.0L Neon way back when and it drove weird and wouldn't break 3-3,500 RPM. As far as having oil in the WGA line check your turbo for any sort of shaft play and inspect your pipes for oil to try to find where the oil is coming from. Also check your coil pack and wires, if you haven't replaced it in an while it may be time.

Last edited by goldfingerfif; 12-27-2016 at 07:34 AM.
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post #7 of 13 (permalink) Old 12-27-2016, 10:30 PM Thread Starter
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Here is what Iīve done so far:

- Replaced the cam sensor (autozone) I think I can put the original back since there was no change.
- Checked and replaced vacuum lines.
- Checked turbo play (looks fine but there was still some oil in the charge pipe and the wga vacuum line. If the check valve in the pcv line was obstructed and maybe the catalytic converter was clogged probably internal engine pressure caused the turbo to leak oil).
- Replaced check valve in the pcv line. The former check valve was failing.
- Checked for codes and cleared computer (no codes).
- Checked WGA (original stage 3) everything looks fine.
- Replaced sparkplugs = no change
- Gutted the catalytic converter = less lag and better acceleration until sputtering happens (iīm not a fan of catalytic converters anyway).
- Checked TPS sensor (voltage looks fine, no jumps voltage increases smoothly)
- Replaced MAP sensor (no change)

So this is what is left unless someone suggest a better idea:

- Check and replace sparkplug wires (car has granatelli wires less than 2 years old).
- Check coil pack
- Check fuel pressure
- Check fuel filter or fuel pump - This would be a headache since stage 3 fuel pumps are not available anymore.
- Check injectors

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post #8 of 13 (permalink) Old 12-28-2016, 05:10 AM
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Do you have a wideband? I would test the fuel pressure while driving the car.
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post #9 of 13 (permalink) Old 12-28-2016, 11:23 AM
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Im thinking it could possibly be fuel related… maybe the fuel filter is clogged up. How long has it been since its been changed? Maybe the possible clog or dirty filter is allowing enough fuel to pass through at part throttle but whenever you give it the beans its not allowing enough fuel to pass through and causing your issues… just spitballing
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post #10 of 13 (permalink) Old 12-29-2016, 12:52 PM Thread Starter
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Iīm also thinking this could be a fuel pressure problem.

Yesterday I got a new coil pack from autozone (just for test, i donīt like autozone crap) and first tested the car with granatelli wires. Couldnīt drive the car, it behaved horribly, I coudnīt eve go to 40 mph. So i guess wires are part of the problem.

By the way, this behavior didnīt happened with granatelli + original coil pack.

I switched back to the original wires and could drive the car normally, but again: at full throttle I had studder, hesitation, lack of power and also, with dab at 2 or 3 the car overboosted. with the dial at 0 i get around 10 psi and dial at 1 i get 15 psi.

I remember when I first installed the S3, i could feel a strong pulse on the fuel line and even the noise from the fuel pump was different. Itīs more silent now and the pulse is not so strong.

Next is to get a fuel gauge and check the voltage and the pressure.

I hope this is the fix for my problem, but in case it is the fuel pump failing Iīm in big trouble because I understand dealers do not carry that part anymore, besides price.

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post #11 of 13 (permalink) Old 12-31-2016, 08:19 PM Thread Starter
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Put new sparkplugs, stock wires and stock coil.

I donīt know why but granatelli wires failed after around a year. The former sparkplugs were almost new but anyways, I put a new set, oem wires and put back original coil and problem was solved.

Iīm glad it was not a fuel problem.

Thanks for all your comments and suggestions!

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Last edited by ralf; 02-09-2017 at 07:44 PM. Reason: that was not the solution
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post #12 of 13 (permalink) Old 01-19-2017, 11:15 PM Thread Starter
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SOLVED: Just another update, I found the real problem: Faulty fuel pump.

Rented a fuel pressure gauge from autozone to measure the gas pressure and found that at idle i got. 45 lbs pressure and at WOT it fall down to 30 and thatīs why the shuddering happened.

I just replaced the fuel pump for a walbro 255, fuel pressure regulator is fine and now the car is completely transformed. Full WOT at 20-25 psi and no fuel cuts or hesitation. The car just accelerates like crazy.

Iīm so happy now!
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Last edited by ralf; 02-09-2017 at 07:47 PM.
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post #13 of 13 (permalink) Old 01-20-2017, 07:51 AM
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Quote:
Originally Posted by ralf View Post
Just another update, I found the real problem: Faulty fuel pump.

Installed a fuel pressure gauge to measure and found at idle 45 lbs pressure and at WOT it fall down to 30 and thatīs why the studdering happened.

I just replaced the fuel pump for a walbro 255 and now the car is completely transformed. Full WOT at 20-25 psi and no fuel cuts or hesitation. The car just accelerates like crazy.

Iīm so happy now!
Glad to see you fixed it and posted the result. +1 to Robdee30
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