95TS 3.8L Misfire REVERSE ONLY

[500hpgtx]

Hi Guys

My 95 TS 3.8L is misfiring on #4cyl ONLY when reverse is applied.
When car is in reverse with parking brake applied, consistantly misfires on
#4. In drive with brake applied and engine load no miss. Neutral no miss.
Car drive ability is great in drive no misfires. 100% misfires on #4 only when in reverse.
Is there any vacuum change or assist utilized with this trans? Possibly vacuum leak? I do not have a vacuum gauge. I changed to a different plug wire and same problem. New plugs installed. Have not swapped coils yet.
I would think a load applied in drive would act similar. Interesting problem.
I am not familiar with this trans, other than the vacuum servo for upshifting I replaced when it was sucking up trans fluid like my old Powerglide in the OLD days...thanks KEV

[Jrs3800]

Kev the 4T60E uses a vac modulator to control line pressure in the trans, Reverse is not actuated by a solenoid, but is a Manual of sorts... Its possible you could have a vac leak, but chances are you would not have a cylinder #4 miss solely.....

Hard to say what the misfire could be... Is the #4 plug wire by chance touching the O2 wires?

I am almost stumped...

[500hpgtx]

Hey Don!

This morning I sarted the van and it ran great! My wife doesn't telll me when it runs great, Just BAD!
I would have to assume that the fuel injector cleaner may have cleared the #4 injector. I had no help with cleaning the MAF, swapping plug wires, reseating connectors to the other sensors. This van has always been sensitive with the idle, and mild stumbling off idle. When I replaced the 3 coil packs because they came with the new ICM, idle was perfect. I replaced the ICM based upon LMP's suggestion that older engines can leave you stranded
de to a failed ICM or crank sensor.....thanks for your concern and reply KEV

[LMP]

understand it is misfiring when you drive in reverse....right? I do not know of any specific connectors that would impact on firing.....but that makes me remember of one incident. I had a Volvo...and the coil was bolted to the firewall. Going uphill or under hard acceleration, it would misfire badly. At steady speed or downhill, it was a rocket.
I had someone at home "torque" the running engine against the blocked drive train and saw the engine tilting on the shockmounts and pulling the hot wire running from distributor to coil ...slightly out of the coil, sparking all over the place, and then reset to normal position when at rest.....
I'm just wondering if "reverse" torque is playing some trick of that sort....

[500hpgtx]

Hi LMP

Aggravating cyl4 miss still there. I swapped plug wires with #6. No difference.(wires 2 years old)
Reseated connectors at MAF, TPS, and MAP? at throttle body area. Worked great for a few hours. Returned. Placed in reverse with E=brake, wiggled connectors at throttle body-no change. Checked harness at fuel injectors no change.
LMP this really smells of an electronic/electrical connector problem.
Does the PCM send signal to the ICM seperate for all 6 cyl? I would think that
next step is to check for intermittent connect at Large connectors at firewall. Probably injector signal from ICM as well.
Hate to take apart connectors at this age vehicle. Wish you could see this one in person. Thankful van runs great otherwise. I know how these problems go.Sometimes a fore-warning. Thanks again for LMP and JRS3800 Help...KEV

[500hpgtx]

Hey Guys!

New Update. I started getting other symptoms when I put the van in reverse gear. The air conditioner clutch began cycling in and out, along with the cylinder4 miss.

I opened up the 2 large connectors at the right of the engine bay, and sprayed them down with WD40. More problems with stumbling idle in drive, and an apparent shudder with the vehicle at 50 mph, that may be from the TCC not locking up.
I bought di-electric grease in the large can size, and coated the connectors liberally at male and female pins for the 2 large connectors at the firewall. Instant perfect idle in all ranges. No shudder at 50 mph.
I cannot say this is the answer, but I have had a hard time working on lab instruments that was connector related.

Also to make my weekend, there was a very large banging noise that increased with rpm. I tried a tensioner pulley, but had a hard time isolating the noise. I was aware it could be anything, but not internal to the engine. Had to get this right fast for the wife, Firstone thought it was the water pump. I said very doubtful, I replaced it about 4 months ago. THey removed it and found it was the Harmonic Balancer! I thought of the possibility, but never had one go bad. Last but not least, was the B.S. window regulator and motor assembly on the drivers side. I found that the tiny threaded bolts came loose and only one was holding on, even though
I had replaced the motor earlier and lock washered and tightened down.
I replaced with larger bolts and nuts with nylon compressors. Fun weekend!

[Jrs3800]

Had to do both windows in mine 2 years ago... Hope it stays together..

Glad to hear the problem may be solved..

[500hpgtx]

Wife and Daughter drove to western Illinois and then drove out to St. Lois to check out colleges.

Van has been running flawlessly for over 1200 miles.

Important Point= Intermittent misfires reverse only cyl4, and air conditioning clutch cycling appear to be resolved at this time. Worth packing the 2 large
electrical connectors with di-electric grease! May prevent chasing ghosts for
a long time....

[Jrs3800]

Glad to hear that the problem seems to be solved... Gotta love an easy fix

[LMP]

Interesting. To be remembered.

[500hpgtx]

Hey Guys! Remember this one? I surely did!!

I knew I would have a return of this problem when the welder replaced the melted wiring harness in our van due to a broken strut tower.

I went through the two large wiring connectors again on the passenger side. i cleaned them with electronic tuner cleaner. packed them with di-electric grease. This time around...no real help!

What I found this time is that the rear wiring harness large connector at the female side has likely a couple of open connections when flexed. Pontiac broke the connector where it bolted on, and left it some years ago. Normally, I would probably consider replacing the female side of the wiring harness that seems to spread to a lot of places.

I flexed the large female connector to where the van runs best(while the engine was running), and wire tied it in that position. I just do not have the time to replace the harness and without a doubt run into a pandoras' box. I worked on blood analyzers for DuPont years ago as an engineer, and old wiring turned into a nightmare sometimes....Cheers KEV

[Jeffrv]

Intersting..but my problem seems to be the opposite, runs reasonably well in neutral and reverse, but major misfire and sometimes stalling in drive.Also 95 TS with 3.8. No obvious vacuum leaks, but all 3 coil packs cases were split open, so changed all 3 and ignition module as well, no improvement.
Almost feels like pcm goes into rev limiter mode at about 1500-2000 rpm, rpm fluctuates about 4 to500 rpms while driving.
Fuel pressure at 32 PSI while engine misfires. MAF all over the clock, rapid fluctuations from 0 to 45, sensor cleaned. In driveway, at idle ST fuel trim about 128, spikes to 180 once drive selected; return to neutral, engine stalls about half the time, or ST fuel trim goes down to 100.
Like you, thinking wiring harness issue..Opened ignition module, MAF, large connector, ignition bypass ( 8 pin) connectors, cleaned packed with dialetric grease. Any suggestions?
Jeff

[Tech II]

No codes are set?

[Jeffrv]

Sorry, no MIL or codes set..seems to be running better once connections cleaned..but problems also happened during unusually high( at least for here) ambient temps. Last tank of gas purchased out of town, now filled up with fuel from my regular station..many variables at the same time

[500hpgtx]

Hi Jeff,

LMP was on the right track with a volvo problem.
I realize now that when our transmission was rebuilt, the mechanic replaced the trans mount. With the broken large rear connector mount, and the bad trans mount, over the years the cable flexing probably was one of the culprits. I do not know of other owners having common issues with the connector pins themselves.
What I would suggest is to unbolt the large connector near the firewall first, and run the engine. With engine running, flex the connector gently, and look for engine surges, misses, (air conditioning clutch disengaging;-) ), etc.
Aggravating, but right now with that connector on our van wire tied in position, the van runs as smooth as silk. As you are aware, electrical problems can be the death of a vehicle. Cheers KEV