Engine sputters around 4k

[MrBurgundy]

Trying to get some insight, as I am coming to a dead end in terms of a diagnosis.

I first began to notice this problem when I'd hit a bump under acceleration, my car would sputter for a split second, but now its intermediate.

Under a load around 4k rmp the engine will sputter/cut out, but not stall. If the car is in neutral it will rev up with no issues, but while driving, the car will start to act up. The car is not throwing a CEL

The fuel pump has been replaced. I'm thinking my DME or some of my injectors are about to take a dump.

Also, the fuel filter has been replaced, no vacuum leaks have been detected and the AFM was cleaned.
Has anyone experienced something like this?

[ak-]

Check to see if the CPS bracket is loose or the sensor itself is loose/not screwed in. Maybe move it closer a bit.
Mine was and I was hitting a brick wall limiter at 4k.

[peterman]

Just had this exact problem. Stutter at 4k. It kept getting worse. Turned out to be the distributor cap. I was reluctant to replace it again because it was relatively new. New Bosch cap solved the problem for me.

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[Kershaw]

http://www.r3vlimited.com/board/showthread.php?t=372569

Check everything mentioned in this thread.

[TobyB]

The 'bump' makes me think either wiring
(connector under the intake, CPS, etc)

or the AFM.

t

[MrBurgundy]

http://www.r3vlimited.com/board/showthread.php?t=372569

Check everything mentioned in this thread.

I just read through it and there is a lot valuable info there. I cleaned my injectors last night and went out for a drive, no more stuttering.. Does that even make sense that injectors would cause stuttering/a hard hiccup around 4k rmp every time?

I still get those hiccups on bumps though, it has to be a bad connection somewhere... or a bad ground.. I'm going to throw a gound from the VC to the strut tower and see what happens..

[Kershaw]

I don't think so. Dirty injectors would get worse as the fuel pressure goes up, doesn't make sense it went away after 4k. However, it could have been your injector harness connections and since you removed and reinstalled, maybe it's a better connection now.

The hiccup definitely sounds like a bad connection somewhere. Might want to replace your main relay as well.

[jtparts]

Cps cps cps, just went through this with a new sensor. I was having a hard time accepting it could be the problem. Swapped, fixed,done.

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[jtparts]

Get it yet?

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[ForcedFirebird]

Some of the things that have caused this for me (customers) when you have a stutter at ~4k-ish, some even felt fine up to then, but felt like the car got stronger at 4k.

WOT switch failure in the TPS: ECU reads the o2 in WOT and makes corrections, not using the WOT maps.

CPS wire: Rubs water pump pulley and makes the ECU go crazy at high RPM

CPS location: Too much gap. Loosen the 2 bolts on the bracket, use a business card to space.

AFM: Wiper track is scraped off under the black plastic cover. Move the wiper to a fresh spot on the track.

Ignition coil: Weak causing recharge issues at high RPM.

Coil to distributor wire: Slight short causing discharge of the coil prior to spark plug.

ECU: Bad ECU, usually goes along with tach output issues (crazy/dead tach).

Dirty fuel tank: Sentiment in the tank (worse since e10 became commonplace). This is especially true if you have the fuel rail with the in/out-lets on the same side. Ethanol-laced fuel sits stagnant and rusts the inside of the rail - starving the engine of fuel at higher RPM. (bumps can worsen the situation) We have been replacing a lot of fuel rails and tanks lately here at the shop.

CTS: The blue coolant sensor is heavily relied on for fuel in Motronic. (see below)

c191 (round injector plug): The CTS and injectors go through this plug, so the above statement my not be a bad sensor, just the signal is not (or barely) making a connection, causing the resistance to be off. Usually if the injectors are having problems here, either the front of rear bank will have issues, not all of them (usually). They ll share 2 power wires here (front/rear banks) and each ground goes individually to the ECU for firing.


The Motronic is so simple, it's often difficult to diagnose without checking all sensors. Usually we start with all multi-meter tests, then go to a fuel pressure test. If fuel pressure test passes, go to a fuel volume test - many times the pressure will be good, but volume won't (you need both).

Even if none of these help, checking/repairing them will ultimately make the car run/start/drive smoother all around.

[MrBurgundy]

I don't think so. Dirty injectors would get worse as the fuel pressure goes up, doesn't make sense it went away after 4k. However, it could have been your injector harness connections and since you removed and reinstalled, maybe it's a better connection now.

The hiccup definitely sounds like a bad connection somewhere. Might want to replace your main relay as well.

I actually replaced the main relay in the middle of trying to figure this out. Also, I took a wire brush and cleaned the harness connector going to the fuel injectors. I think that it was either the main relay or the pins in the harness were not making a decent connection.

Anyways, car has been running perfect since. So, I think its fixed

[ForcedFirebird]

If it was the c191, good chance it will come back. The wires turn green and corrode where you can't see it under the sheathing, and "grows" back to the connector. Have a car that we keep cleaning every few weeks, owner refuses to replace. :(

[Gregs///M]

Cleaning the AFM does nothing, it must be refurbished to become reliable again. See my thread on AFM refurbishment to see why you get the misfire type symptom, I have signal graphs that outline how it can confuse the DME.

[MrBurgundy]

If it was the c191, good chance it will come back. The wires turn green and corrode where you can't see it under the sheathing, and "grows" back to the connector. Have a car that we keep cleaning every few weeks, owner refuses to replace. :(

If it comes back, I'll just re-wire it or find a replacement. Hopefully, its not the main harness.

Anyways, thanks for all the tips guys, problem is fixed as of now.

[MrBurgundy]

I actually found the problem for this, it came back the other week. The PO of my car routed the CPS cable in a way where there was absolutely no slack in the cable. When I would hit a bump or rev the engine out it would yank on the cable and cut the connection.

Super happy I figured this out without pulling half the hair out of my head.