Reverse engine surge....anybody solved it?

[morgan]

My 94 K2500 with 4L80E has the typical reverse surge problem. A sudden, momentary rev of the engine when moving in REVERSE. It is very random. Only happens periodically, and usually only once every day or so, then dissappears for weeks/months.

Anybody solved this one yet??

[markrinker]

Yeah. Don't back up. smile.gif (Sorry I couldn't resist.)

I have never experienced this with trucks #1 or #2 and I back up with heavy loads daily.

Could it be a transmission 'slip' that appears as an engine 'surge'? My gasser #3 with 4L80E transmission did this before reverse completely let go. It was noticeable empty, but fried backing heavy loads up inclines.

It would seem possible to me that the higher torque of a diesel (even at idle) could easily sound like a 'surge' when in fact its overpowering a worn reverse clutch pack.

[morgan]

You know, that could very well be one part of the problem. Thanks for that alternate suggestion.

Except that the motion of the vehicle also surges backwards suddenly.

Maybe...just maybe there is a slip that I cannot percieve, then when it does "bite", the sudden mostion is more easily percieved than the micro-slip before it? So the slip allows the engine to rev, then when it catches, it surges. I could buy that excuse I suppose.

I'll try to be even more perceptive next time it happens.

[CareyWeber]

Its likely a wiring issue or dirty speed sensors in the trany.

Mine quit doing it after cleaning my speed sensor.

On my 4x4 cleaning the rear one is very easy 10 min job.

Carey

[ace58]

I have a reman GM transmission with less than 10K miles and it still occurs. It does act like a power surge over a transmission issue, but I am all ears for a definition/solution.

[markrinker]

A transmission with an apply problem in reverse will still move, but there is usually a noticeable shudder. Kinda like holding a manual clutch partially engaged and hitting the gas.

Hoever, we might still be on to something here. Both of my 1994 trucks spend LOTS of time in reverse, and never have exhibited this problem. They both have been plowing snow for 11 years since new, and would have MILES and HOURS in reverse as a result. My drivers are pros and work in reverse about as fast as they plow forward - seriously.

Assuming that the 'normal' truck doesn't get used in reverse nearly as much, maybe the culprit is something in the linkage, or an internal apply problem from something gummed up from (relatively) low useage.

How about some Trans-Medic followed by a flush and fill?

[landrea]

I have a similar problem,when my 2000 is idling in park it will once in a while just jump to about 1000 rpm for a split second.It does not seem to have any pattern it is totaly random.It did this with the old and new engine , new and old inj. pump,new and old fsd,I'm stumped.

[Cowracer]

Morgan,
I have had the same problem. I damn near ran over an old lady because of it. :eek: It gets your attention.

It wasnt too long after it started doing that, when the truck started dying in the classic FSD failure mode.

Tightening up the transistor screws solved both problems.

Tim

[morgan]

I am not familiar with the transistor screws. Which ones? where?
thanks

[Hubert]

I had a short in my trailer lights that allowed the truck to run after I cut the key off while in reverse. The reverse light circuit comes from a common node powering the pmd. When in reverse the circuit closes and power runs back to lights and grounds.

As sensitive as the electronics are these trucks a little intermittent extra voltage or something could give a little hiccup. I assume rev lights work like they should? Any added on trailering lights or reciever hitch? My reciever hitch did not make good ground at first. The undercoating and paint were too thick.

[MTTwister]

Morgan - The transistors on the PMD / FSD I believe. You need to be able to get to the underside of the PMD - ie remove it form the pump is that's it's location. Take off the balck plastic covers over the transistors, on the "bottom". The nuts need to be about finger tight ( on the 1/4" nut driver handle) + 1/8 turn. ( There's a torque spec out there somewhere. )

Search on PMD / FSD - some hugh discussions on this problem, but they seem to come looses from heat cycles, and potentially "break" an internal solder joint. Tightening the nuts pulls the
transistor pins back into contact.

[DA BIG ONE]

Most common cause of this surge when in reverse is a bad "manifold pressure sensor" in the trans pan, this sensor measures tranny pressure and sends that measurement it to tranny controller.

If not corrected it will go into what I call the self destruct mode because the computer will not know which gear the tranny is in. Look for code 1810...

[morgan]

Cowracer and MTTwister:
Oh OK, I know about the thing between the PMD and the cable harness. I call it a resistor.

TomAtoe, Tomatoe, whatever.. thanks!

[moondoggie]

Good Day!

What I've experienced definitely is NOT a tranny issue. The engine takes a very definite, brief jump in rpm. It has only happened to me when putting it in reverse. [i]

[Barry Nave]

Yea,good reading ;) I gave up on the FSD and for now only time will tell how the installed SOL-D works. So far only good things with it.

[Cowracer]

Originally posted by morgan:
Cowracer and MTTwister:
Oh OK, I know about the thing between the PMD and the cable harness. I call it a resistor.

TomAtoe, Tomatoe, whatever.. thanks! No sir! Not the resistor. TRANSistor. If you examine the bottom (mounting face) of the FSD unit, you will see two plastic covers shaped like an elongated diamond. Under these covers are power transistors that are attached by two small screws with nuts. These nuts loosed up and cause problems.

Tim

[charliepeterson]

For anyone with this surging in reverse try this. In park slowly bring the RPM's to about 1000. If the RPM's rise with no additional foot movement the IP is failing internally. I experienced this in the snow/poor traction condition. After checking everything out I tried the neutral trick and it did it very easily all the way past red line. Take your foot out and the rpm's drop back to 600.

After the pump swap the truck is making money now for two years with no more problems. The SES only came on for an engine over rev. It could be that the transmission is giving the engine just enough resistance to keep it from running away. Reverse and overdrive are the same clutches.

[morgan]

Yes, of course: the twin transistors nested within the PMD. I know about those and have removed the small plastic covers from them and have gently "re-torqued" the small hex nuts that hold them. I was thinking too hard, I am with you now.