Engine Missing or Bad Tranny

[Bunson]

1995 Pontiac Transport
114,000 miles
3.8L SFI OHV 6 cyl

HELP! While driving, our van will occasionally give a noticeable jerk. Like a clunk or a thunk. It feels like a miss and it is only momentary. It seems to only happen when pushing on the accelerator - but it doesn't really seem to be load related. It doesn't seem related to bumps in the road either. I can be cruising down the interstate at 65 and give a little push to keep the speed constant and I feel it. It started years ago and would only do it on rare occasions - perhaps once or twice a year. It now happens fairly regular - as much as 5 or 6 times on a 20 mile trip. It seems to happen for speeds of 35-40 mph and up.

At first I thought the problem might be the tranny slipping, but now I think it may be a sensor or module or something that is affecting the timing or ignition system and creating a miss. Also, something new - this past weekend I had trouble starting the vehicle after driving about 30 miles. It cranked, but wouldn't fire-up first thing like it always does. I'm not sure it is related but I thought I should mention it.

I replaced the plugs and wires, but that didn't help. (the old plugs looked great). I siphoned out about 8 quarts of tranny fluid and put in new fluid, but that really didn't seem to change anything. I never had the tranny fluid or filter changed previously.

I bought an Actron code reader so I could read the codes.

The most common codes have been (almost every time we use the van):
P0361 - Ign System Problem / Elec Spark Timing / Est not Toggling
P0321 - Ign system Problem / 18X Interrupts Lost Signal

I also had two of these codes: P0101 - Mass Air Flow / Sensor Signal Failure

One of these codes: P0341 - Ign System problem / Camshaft Sensor / Intermittent Signal


I'm mechanical enough to replace parts. But, if anyone can provide some suggestions on where to start I can certainly use the help.

These are things I am thinking of replacing:
Ignition Control Module
Ignition Coil Pack(s)
Powertrain Control Module
Throttle Position Sensor
Camshaft Position Sensor

[Jeffrv]

I have the same year/engine as yours, and about 10 years ago it also acted the same way, eventually got worse to the point it would stall out while driving ( usually restart immediatly tho). Took it it to a garage, they changed cam sensor, problem went away for about 10 months, then came back. New staff there, they changed a pile of parts that didn't need to be changed and didn't solve the problem, so went to GM dealer after it quit on 4 lane highway. They changed crank sensor, and have had no problems since.
Others have indicated that the ignition module is prone to failure, altho mine is still factory, and PCM's noted for failure, but again, mine still factory.
Crank sensor is where 18X and 3X signals originate, and are processed by ignition module, so I think that is where I would start.
Good luck
Jeff

[LMP]

Totally agree with Jeff. All signs coincide. Changing the crank sensor or at least having one at hand just in case...(meaning also you have all you need to pull the balancer out)....is a natural at that age.

http://www.automotiveforums.com/vbul...d.php?t=736818

[Bunson]

WOW! Great info. Thank you. Very helpful!

I'm relieved that the problem seems to be pointing towards an ignition issue and not the transmission. I ordered an Ignition Control Module from eBay and will try installing that first. (new AC Delco ICM for $56)

The crankshaft sensor looks like more than I want to tackle right now. So I will replace the ICM and possibly install a new Camshaft Position Sensor since those are realitively inexpensive and I can install them myself. I may buy a single ignition coil and swap it around to see if that fixes it. If these don't fix it I will farm out the Crankshaft Position Sensor to a local professional. I'm afraid to find out what that is going to cost.

I cleaned the Mass Airflow Sensor last night and looked over the wires since I'm stuck waiting for the ICM to come in.

Thanks for taking the time to help.

[Bunson]

I had the Crankshaft Position Sensor replaced by the GM garage. None of the local garages wanted to do it. Total cost was $272.

After 500 miles it seems the new CKP Sensor has cleared up these codes:
P0361 - Ign System Problem Elec Spark Timing EST Not Toggling
P0321 - Ign System Problem 18X Interrupts Lost Signal
(P0341 - Ign System Problem Camshaft Sensor Intermitent Signal)

I had been getting P0361 and P0321 everytime we used the van. I only had the P0341 once.

I think the CKP Sensor also cured the stalling and hard starting. I haven't done anyting beside the CKP sensor so far. I wanted to post this info in case anyone else encounters this problem.

Thank you for the info about replacing this.

=================================

However, I still have the problem described in the first post. When cruising or starting out, and I push on the accelerator a little, the van jerks - like a mis-fire. (I've read about the torque converter problem, but I don't think that is the problem.) Also, on the highway it did something new. I was cruising down the highway, foot off the accelerator and the engine stumbled. The RPMS dropped then got back to normal.

I'm still getting P0101 - Mass Air Flow (MAF) sensor Signal Failure. I cleaned the MAF with a Q-Tip and alcohol, but that made no difference. I ordered a remanufactured ACDelco MAF from eBay. From what I have been able to read, a bad MAF can cause the symptoms I am having.

I'll post results after I replace the MAF and in the mean time if anyone has any ideas...

[Jrs3800]

Do the MAF first...

But I suspect that you will still have a code 1361( there is no 361, some Scan Tools just report it that way )... This is an issue where the ICM and PCM don't do their handshake allowing the PCM to take over timing, if this happens you'll be stuck in 10* Module timing...

Fix the MAF issue first and get back to us...

[danielsatur]

The engine needs to have good horse power to deliver to a hydrostatic transmission, any engine miss could give symptoms of making the transmission shutter.

Troubleshoot engine 1st.

An engine miss could be one of the four strokes that's missed, and you got 6 cylinders.

1. Intake - MAF Air/fuel mix control from the ECU.
2. Compression (low compression)
3) Power (ignition) clean + test sensors, and check for spark.
4) Exhaust (bad cat)

Random misfires on random cylinders-
Check MAF, Air filter, clean throttle body & plate, fuel filter, and check fuel pressure.
You need alot of Air/fuel to get horse power.
Have catalytic converters checked

[500hpgtx]

Take a look at my previous post 95 Transport 3.8L Misfire REVERSE ONLY

Possible connector issues....KEV

[Bunson]

CRANKSHAFT SENSOR
=================
I had a new Crankshaft Sensor installed, and these DTC's cleared up:
P0361 - Ign System Problem Elec Spark Timing EST Not Toggling
P0321 - Ign System Problem 18X Interrupts Lost Signal
I think this fixed the hard starting problem too.

MASS AIR FLOW SENSOR
===================
I put in a new Mass Air Flow Sensor today. The new MAF Sensor has cleared up the the misfire like symptom that was causing the hard jerk. The jerking under mild acceleration has stopped. Progress!! It also cleared up DTC - P0101 - Mass Air Flow (MAF) Sensor Signal Failure. As a test I cleaned the old MAF Sensor and put it back in - when I did the jerking came back. I put the new one back in and the problem went away again.


NO MORE JERKING/SHUDDER - BUT STALLING IS WORSE
==========================================
After I put in the MAF sensor I thought everything was good to go. I took the van for a test run and it ran great.

But - I used the van later in the day and the van is stalling worse than ever now. This isn't the same misfire like jerk that I was having - this feels more like a fuel issue. It seems to happen when I let all the way off the gas. The gauges don't go wacky - they just drop to 0 RPMs, etc. and the engine sometimes dies. I put it in neutral and it starts right back up. Sometimes the RPMS drop, but then come back. As long as I'm feeding gas it seems to be ok. I don't get a SES Light, but when I checked the codes I had P0406 - Linear EGR Pintle Position - Position Error. I currently have a BWD brand EGR installed that is 18 months old.

I'll check wires some more again tommorrow - I've been looking and looking and nothing looks amiss.

Sounds like a bad EGR dosn't it? This is like whack-a-mole - fix one thing and another pops up. I hope I'm almost there. Thanks everyone for your help so far.

[Bunson]

This morning I hooked up the Actron CP9145, put it in View Data mode, and took the van for a short run while I watched the EGR readings:

EGR REQ(%)
EGR VLVPOS(V)
EGR VLVPOS (%)

The EGR REQ(%) climbed as I accelerated, and went all the way up to 100. The EGR VLVPOS(%) never got above 12. I assume these readings indicate the per cent that Pintle is open and that they should match.

I took the EGR Valve off and cleaned it, then took the van for another run. (Not much carbon but the valve seemed a little sticky) This time EGR VLVPOS(%) got up to 21, but never above that. EGR VLVPOS(V) stayed around 0.7 most of the time, never went above that. I guess VLVPOS(V) indicates voltage but have no idea what it should be.

I am still getting: P0406 - Linear EGR Pintle Position - Position Error. This can easily be explained by the vast difference between REQ(%) and VLVPOS(%).

I suspect a bad EGR Valve, and I ordered one from eBay ($99 + shiipping = Ouch). I guess a bad PCM and connections are still possibilities. I will keep checking the wiring and connections.

Van still stumbles, stalls out, and hesitates on acceleration. Generally running rough.

[Bunson]

NEW EGR VALVE
==================
I put in the new EGR this evening. The stalling, hesitation, and rough running are gone. All cleared up.

Everything is now fixed!!! All systems are go! No more CES lights. She is running great again.

On Monday when I was still waiting for the EGR to come, I put a coat of wax on her thinking that if I couldn't fix her and she went to the salvage yard at least she would look good. I wanted her to at least go with dignity.

I wrote losts of stuff in my posts - I hope the information can help someone else who comes here looking for help. Thank you to all the great folks who helped me (I never would have gotten the Crankshaft sensor figured out on my own). It is a wonderful thing you do by providing help to others.

Bunson

[danielsatur]

After you weeded out a bad MAF sensor, and EGR valve, did the transmission shutter went away?
A open EGR valve when cold, is like a vacuum leak going to your Intake.

[Bunson]

Yes. The MAF was the culprit making me think that the transmission was missing or shuddering. At first I thought it was the tranny, then I thought it was a misfire. Ended up it was the MAF. I tried cleaning it, but I think it was electronically fried.

I read somewhere that a malfunctioning MAF can mess up the injector timing, or confuse the computer so that it resets the injector timing. I think it was doing this and that caused the jerk that I felt when driving.

[Jrs3800]

The MAF has nothing to do with injector timing, this is all controlled by the Crank and Cam sensors( at least the readings the PCM receives and actuates from them ) The MAF is simply used so that the PCM can determine the Mass or weight of the air to correctly calculate the fueling needed at a given load cell ) The PCM will expand or shrink the Injector Pulse Width depending on the load factor and the MASS of the air entering the throttle body... If the MAF is having any issues it can cause a series of driveability issues...

Glad you got the EGR issue figured out, what was really happening is that the PCM did not know where the EGR pintle position was so the PCM could not correctly control the EGR, causing driveability issues.... I too have had the same issues with a few Linear EGR's... Once you have a Pintle Position Error its time to replace the EGR...

Good work...