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1991 Chev 3500 chugs/shakes when I take my foot off the gas

A

AcerRu

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Victoria BC
Hi There

I am new to this site and this is my first post I searched and found nothing about this problem I have with my 1991 Chev 3500 with a 6.2 Diesel engine.

As I am driving with my foot on the accelerator the truck drives fine, as soon as I take my foot off the pedal the truck shakes to and fro quite violently, a lot like someone who is new to driving a standard when they take their foot off the clutch too soon, (it is a standard transmission truck, has a new clutch has done this with the old and new clutch), It doesn't do it all the time but I would say most of the time, if I give it a little gas it will sometimes will go away, if I put my foot on the clutch it will go away, but I don't particularly like the idea of driving around with my foot on gas or the clutch when I don't need to.

Any help with this problem would be greatly appreciated and I thank you in advance.

Michael
 
first off, welcome to TTS. now it's time to get for some info.
how many miles on the engine?

which transmission?

what other work has been done on the engine?

any other issues? rough idle, hard starts, missing?
 
Hi

There are only a 109,000 km or 69,000 miles on the truck, I am not sure of the transmission, I have left a message with my mechanic to call me back on that one. The truck is in fact a 1992 and the transmission is manual transmission, I will get more info in an hour or so.

It has new batteries, new glow plugs, air and oil filter, thermostat, starter, and the brakes were re done as well.

It starts fine, (as long as you have the clutch pedal planted firmly to the floor), idles fine, I was having an issue with stalling when I put my foot on the clutch, but that seems to have been repaired, there was bare wire that was hitting the clutch pedal.

I have only owned it since April and that is all I know. It was owned by a local municipality for its entire life prior to that.

That is all I can tell you for now.

Thanks for your interest!!!

Michael
 
Excuse my ignorance but what is the LP? I am assuming it is a pump. How would check to see if the pressure is where it should be?
 
LP = Lift Pump. I am not sure if it is the same as the newer trucks or not, if it is it has a water drain T handle on the T stat crossover. You can hook up a pressure gauge there with the T handle open.
 
ok, your transmission is called an NV4500(new venture). as for the LP, electric or mechanical? which body style are we dealing with, the 82-87 or the 88-98? the other think to check is the rubber in the crank pulley. does it happen to be rough and the belt by chance?
 
Thanks

I will check the pressure at the T handle with it open. What should I be expecting for psi/bars for proper functioning? The body style is the '88-'98 style and the belts look good, no sign of wear or deterioration. I will check the lift pump to see if it electrical or mechanical, my thought is that it is electrical.

Thanks again for you help

Michael
 
Sounds like you have an LP that is not working or not getting power.

In your year, it runs solely on power from the Oil Pressure Switch/Sender unit, while the truck is running. The OPS is a certain failure item after several months or miles. Most of us with older non OBD2 truck perform a OPS relay modification, which removed the load from the OPS and puts it on a separate automotive relay rated for more current. You should read this thread thoroughly. Your truck will work like the OBD1 trucks, even though you have no computer in yours. Much of the OBD1 specific stuff is discussed in the second page of the thread, but the first page has all the fundamentals in it.
http://www.thetruckstop.us/forum/sh...t-Pumps-amp-OPS-operation-and-troubleshooting

So first have to make sure the LP is getting power then make sure the LP itself works. Otherwise the IP has to suck the fuel from the tank which creates a vacuum in all of the fuel line and any pinhole can introduce air in the fuel line, where pressure would have prevented it.
 
Sounds more like Death Wobble to me. How's your front end ? No LP on a 6.2 will cause a seriuous lack of power and probably smoke alot. a DB2 can pull it's own fuel but it will not run good like a DS4(Later model Injector Pump used on 6.5's). Check the drivesahft too.
 
Is it running better? You should consider the OPS relay modification to get the LP power off of the OPS. Its on my list of essential modifications for reliability. Its also fairly simple and quick to get done.
 
It is running much better. How do I go about taking the LP off the Oil Pressure Sensor?

It is still stalling when I put my foot on the clutch as it comes into a stop, generally when it is warm but occasionally when it is cold. I found an exposed wire which when we depressed the clutch pedal it was touched by the pedal. I thought that was the cause for sure, I re wrapped and routed it over the steering column but it is still doing it, intermittently but fairly consistent. Any thoughts on why it is stalling?

Thanks

Michael
 
I dont know how its done, and I know little about the DB2, but I wonder if you have the IP out of timing. Maybe its even loose on the timing cover. If the truck is a real dog, then I might try advancing the injection timing by rotating it towards the drivers side.

To get the LP off the OPS, just cut the line that sends power to the LP, leaving plenty space on both sides to splice onto both ends. Then put the side going to the LP on the output of an automotive relay, with battery power incoming, and the OPS ouput powering the relay coil, ground the other side of the relay coil. Attached is a schematic I drew for also adding priming function during glow. 91-93 was supposed to have priming per the manuals, but not sure anyone has it working that way. You could still wire it this way I drew it for priming funciton as well. Ignore the bottom option, the top one is better, and the protection diode is optional. If you cannot read it send me a PM and I will email it to you.
LP relay mod.jpg
 
If you suspect timing just look at thte marks. The one on the case it staright up and the one on the ip is "usually" a hair to the drivers side.
 
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