'94 K1500 "lurching" in reverse...

[brianblack138]

I've noticed something very infrequently with my truck... I bought it used in november with only 108k miles on it and it drives great (starts right up, no bad smoking, good solid accelleration) but a couple of times i've noted that when I throw it into reverse (it's an automatic transmission) the truck will lurch a bit. Almost like something is stuck and then slipping... I'm new to the whole mechanics thing, but to me this seems like it could indicate a problem with the transmission. Does anybody have any ideas what could cause this?

[DA BIG ONE]

The 4L80e has a manifold pressure sensor inside pan which measures tranny pressures, when it starts to fail you will that lurching.

Check your codes.

[moondoggie]

Good Day!

I've experienced similar with our Sub - it feels just like someone very briefly floored the footfeed at the instant it went into reverse. The engine revs quite high but only very briefly, & without a firm foot on the brake bad things would happen behind me. Mine definitely does NOT feel like tranny trouble, except inasmuch as it might be initiating whatever's going wrong.

I'll be following this one...

Blessings!

[brianblack138]

moondoggie, thats EXACTLY how it feels!

DA BIG ONE: I checked the codes and nothing came up. I'll give them another check and i'll post back the results. I'll also double check for any leaks with transmission fluid. I've noticed an oil leak, but maybe it's really transmission fluid.. I'll have to lay some paper down and see exactly where it's falling. For the most part the truck has been solid, but as is the case with any 12 year old truck, gaskets and hoses degrade and fluids start to leak. You fix two things and in the process something else breaks...

[BrentN]

My 99 does the reverse lurching occasionally as well. I dont really notice it when you immediately put it in reverse, but as you begin rolling backwards with the foot on the pedal, it will lurch. It seems like it does all of a sudden get a burst of fuel, like there is a low speed fuel metering problem. Never does it in forward gears, only reverse. Sometimes you need to be carefull if you are near other objects and it gives you a burst.

Question:
1. Is the pressure switch only something that monitors reverse line pressure?
-If so, it being bad would make sense, since the problem doesnt seem to manifest in forward gears.
2. Has anyone changed out this particular pressure sensor? How much is it?
3. Is the sensor located in the pan on the valve body or is it external. This one was answered by "Da Big One", its in the pan.

I would like to get to the bottom of this one as it is a potential parking lot dent waiting to happen.

Thanks,

[Cowracer]

Good Day!

I've experienced similar with our Sub - it feels just like someone very briefly floored the footfeed at the instant it went into reverse. The engine revs quite high but only very briefly, & without a firm foot on the brake bad things would happen behind me. Mine definitely does NOT feel like tranny trouble, except inasmuch as it might be initiating whatever's going wrong.

I'll be following this one...

Blessings!

It has been suggested that this is a indication of a PMD starting down the road to failure. My truck does that from time to time, and if I dont get in and tighten the transistor nuts right away, it will get worse, and I will start to get some stalling.

Every single time I tighten the transitor nuts, the surging in reverse goes away.

Also, I have learned NOT to shift into reverse unless my foot is firmly on the brake. I almost clobbered an old lady walking behind my truck. Scared me as bad as it did her.

Tim

[BrentN]

It has been suggested that this is a indication of a PMD starting down the road to failure. My truck does that from time to time, and if I dont get in and tighten the transistor nuts right away, it will get worse, and I will start to get some stalling.

Every single time I tighten the transitor nuts, the surging in reverse goes away.

Also, I have learned NOT to shift into reverse unless my foot is firmly on the brake. I almost clobbered an old lady walking behind my truck. Scared me as bad as it did her.

Tim

Tim,
I dont disagree that when a PMD is going south, it certainly could cause this condition.

As for mine, it has done it since I owned it (90,000miles when I purchased) and did it up and through a new GM Pump and PMD under warranty last year. I would think that if it was a PMD, that it would exhibit the same symptoms in forward gears.

I think I am going to try the pressure switch and see if that helps.

[brianblack138]

(well, new to me, but bench-tested good) and am planning on remote mounting it with a #9 resistor as soon as I drill the holes in the heatsink. I wonder if i'll see any change...

As a rule I never shift into reverse without my foot on the break, but i'm just worried about potential for problems in the future.

Brent, let me know how difficult a fix the pressure switch is... If it's an easy fix, and a cheap part, I might as well replace it.

[DA BIG ONE]

My 99 does the reverse lurching occasionally as well. I dont really notice it when you immediately put it in reverse, but as you begin rolling backwards with the foot on the pedal, it will lurch. It seems like it does all of a sudden get a burst of fuel, like there is a low speed fuel metering problem. Never does it in forward gears, only reverse. Sometimes you need to be carefull if you are near other objects and it gives you a burst.

Question:
1. Is the pressure switch only something that monitors reverse line pressure?
-If so, it being bad would make sense, since the problem doesnt seem to manifest in forward gears.
2. Has anyone changed out this particular pressure sensor? How much is it?
3. Is the sensor located in the pan on the valve body or is it external. This one was answered by "Da Big One", its in the pan.

I would like to get to the bottom of this one as it is a potential parking lot dent waiting to happen.

Thanks,

The sensor is in the pan, it senses all pressure, generally it shows signs of defect in reverse first, this is what happened to me. As it gets worse, the lurching will manifest in forward gears then grinding of gears and then self destruct mode because controller can no longer control.

CODE 1810

http://www.transmissionspecialty.com/

[BrentN]

Da Big One,
When you said a sensor, I assumed something akin to the Oil pressure sensor, I went to the web site...is this what you are talking about..a pressure sensor manifold?
http://www.transhardparts.com/parts/parts/GM%20Manifolds.htm

Depending on where you get it, it looks like about a $25-30 part.

Thanks,

[DA BIG ONE]

Da Big One,
When you said a sensor, I assumed something akin to the Oil pressure sensor, I went to the web site...is this what you are talking about..a pressure sensor manifold?
http://www.transhardparts.com/parts/parts/GM%20Manifolds.htm

Depending on where you get it, it looks like about a $25-30 part.

Thanks,

That little part when failing can cause big problems leading to BIG $$$$ in damages.

[chickenhunterbob]

for 3 years now that I have frequented these sites / boards, this has come up from time to time.

There has never, to my knowledge, been a conclusive diagnosis.

Mine does it, intermittently, every now and then, while switching from OD to R.

Short burst of not needed oomph.

One of those 6.5 quirks.

Many have given speculative causes, PMD, this sensor, or that, some even suggest to replace the transmission.

Learn to live with it, it seems a rather common occurance.

[DA BIG ONE]

Sonnex makes a replacement reverse boost valve and sleeve to keep excessive reverse pressure from damaging case. Designed after 97 and forward 4L80e self regulating reverse boost valve which eliminates tranny damage from high reverse pressure levels.

Yes, GM did screwup costing the unlucky end user untold BIG $$$$ but finally in 97 they fixed this issue.

The Code 1810 issue still exists, pressure sensor manifold "failure" it can and does cause total 4L80e failures.

[moondoggie]

Good Day!

Does any of this tranny stuff account for the unmistakable rpm spike I always get when my Sub does this? Or are there maybe at least a couple different things that can cause very similar symptoms?

TIA & Blessings!

(signature in previous post)

[DA BIG ONE]

Good Day!

Does any of this tranny stuff account for the unmistakable rpm spike I always get when my Sub does this? Or are there maybe at least a couple different things that can cause very similar symptoms?

TIA & Blessings!

(signature in previous post)

This tranny problem w/pressure sensor manifold code #1810 I had a few times. First it would surge or lurch when placed in reverse w/foot off pedal. Then it manifested into doing the same in forward gears once and awhile then grinding of gears in turn locking rear wheels while moving forward, banging gears violently then tranny failure. Kind of a self destruct situation. If anything else can cause this I do not know.