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Discussion Starter #1
Hi guy I'm brand new to the forum. I just bought a 93 Chevy 6.2 ext. cab and I'm having a problem with it. Here goes. The old owner put a jasper reman engine,transmission and front diff 10k ago. I believe him cuz I found the warranty paperwork inside the truck. It sat in his driveway for 2 years not running. My father in law bought the truck got it running and sold it to me. He can't remember what he did to get it running. Well I bought it 3 days ago and it ran like a top. I put fuel in it then later that day it started to act funny. It would bog under load or even the slightest of hills, when it did this it was blowing blue smoke and when i took my foot off the pedal it would die. The filter light was on so I drained the filter from the water valve into a pickle jar and got about 1/2 of red rusty water so I replaced the filter bled the system and it ran good for about 2 miles then it happened about 7 more times before I got home (12miles) each time it was harder to restart. When I finally got it home I left it idling and opened the water valve, no fuel no thing came out. This morning I go out start the truck open the valve and could have filled a gallon jug if I wanted to. No water just clean pure diesel. I'm thinking my electric lift pump is done for I bought a new one today but havnt installed it yst . Please give advice this is my only vehicle now and I have to get it going, oh plus I live in the mountains so this whole bogging on a slight hill thing ain't gonna cut it. Thanks in advance.
 

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Correct me if I'm wrong because I am a diesel rookie but the IP will draw a little fuel on its own but not enough to handle any kind of load correct? And I'm curious but being that my truck has the electric lift pump shouldn't it pump fuel out of the air and water drain valve with the key on engine off? And does the pump make any audible sound with the on?
 

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The IP should draw enough to run, even down the highway. At least this was true for me with a non-functioning mechanical pump. I drove around for a month or two with a bad mechanical lift pump. The electric pump might be different.

The pump will only typically run for 3 secs after you turn the key on if you do not start the engine. You might be able to hear it as a slight whine. If you have the air bleed valve open, and cycle the key, you should see fuel come out if the system is primed and the pump is functional.
 

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Welcome to Diesel Place!

1993 6.2 with electric lift pump....Unfortunately we do not have a 1993 set of truck manuals on the Forum. So here is a SWAG:

On a 1995 6.5L TD with an electric lift pump, the lift pump is powered through the Oil Pressure Switch (OPS). The OPS is mounted behind the driver's side head. See the pictures here: http://www.dieselplace.com/forum/63-gm-diesel-engines/21-6-5l-diesel-engine/39350-reference-material-lift-pump-ops.html#post702583. The OPS serves two purposed: (1) powering the oil pressure gauge (2) sending electrical power to the lift pump when it sense oil pressure and shuts down the lift pump when there is no oil pressure.

The OPS can burn out in the part that powers the lift pump but work fine to power the gauge.

If you can locate the OPS where I think it might be, see if the wiring harness has three wires coming out of it. IIRC on my 1994 they are orange, gray and brown. If you have 3 wires, I am guessing your lift pump is powered via the OPS.

Another thing to look for is the Lift Pump Relay. Here is a picture: http://www.dieselplace.com/forum/63-gm-diesel-engines/21-6-5l-diesel-engine/683330-fuel-pressure-oddity-10.html#post6784033. On the 6.5L trucks this relay is mounted to the passenger side of the firewall. The second picture shows how to jump this relay to power the lift pump. If you have this relay, try jumping it to see if the electric pump works by opening the WIF drain.

If it works, the lift pump is fine and the OPS needs to be replaced. Again I am really guessing here, but if you have a bad OPS, get an AC Delco D1808A OPS. Do not waste $$ on any other brand as the other brands burn out about as fast as you can install them.
 

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Discussion Starter #6
That's what I thought. The problem happens after driving a couple miles almost as if once everything gets warmed up something stops working. My thought was since I have an electric lift pump that its getting hot and breaking down not supplying fuel as it should. If it could be anything else please let me know. This is my first diesel so I'm not sure what everything does.
 

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And I'm curious but being that my truck has the electric lift pump shouldn't it pump fuel out of the air and water drain valve with the key on engine off?
In a word, no. This feature did not come in until the 1996+ 6.5L models


And does the pump make any audible sound with the on?
Mine makes a slight chatter sound.

BTW, if you hear it running after the engine is shut off, then it is definitely powered via the OPS I mentioned earlier and will run until oil pressure is below 4lbs of pressure (give or take)
 

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Discussion Starter #8
Thanks for the input on the OPS I didn't know that. Since we are on the subject what exactly is the oil pressure gauge supposed to read at idle. When I first start my truck its almost at 40psi once its warmed up some it drops at idle drastically to around 15-20psi and while driving its around 30-35psi. So would this be a sign of a faulty OPS as well?
 

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Thanks for the input on the OPS I didn't know that. Since we are on the subject what exactly is the oil pressure gauge supposed to read at idle. When I first start my truck its almost at 40psi once its warmed up some it drops at idle drastically to around 15-20psi and while driving its around 30-35psi. So would this be a sign of a faulty OPS as well?
Hot idle anything over 10lbs is OK.

The two functions of the OPS that I mentioned are separate within the construction of the OPS.
 

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What Freddy said. Sounds like the pump is working when it gets power.
I would think the OPS relay and or the pump is the issue.
 

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One more thing. I am guessing you have an electric lift pump that was part of the original GM factory design.

If a previous owner replaced the mechanical lift pump with an aftermarket electric lift pump then none of what I've posted will apply to your truck.

So check to see if you have the lift pump relay. That will confirm that you have a GM designed electric lift pump.
 

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Discussion Starter #12
I looked today and have a block off plate where a mechanical lift pump would mount but again the previous owner replaced the engine 10k ago so maybe jasper put the block off on it. I hope the parts store has an OPS for it because I already have a new pump ready to install I might as well cover all my bases.
 

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Replace the OPS first. That is usually what fails.

As I said earlier you can test the lift pump by jumping the lift pump relay. This bypasses the OPS and powers the lift pump directly. This is good for bleeding air out of the air filter and in emergencies if the OPS fails.
 

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Sounds like a lift pump to me. But then again when mine failed the truck would still run down the road. it just had a really hard time starting. And yes, the lift pump click/thunks when it's on. It doesn't hum like the gas pumps.
 

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Discussion Starter #17
Thanks freddyack I will try this tomorrow. How much does the OPS usually cost and what's the chances the parts houses will have them in stock do you think? Thanks so much for the help
 

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$30 or so for AC Delco D1808A.

If you need one ASAP, you can try a local GM Dealer. GM Part # 19244501

I just checked Oreilly's. They can get them but takes 2-3 days. $38: ACDelco D1808A - Engine Oil Pressure Gauge Sensor | O'Reilly Auto Parts

You can buy one of the in stock brands (BWD, etc). But you must do the OPS Relay Mod. Here is a link to the mod: http://www.dieselplace.com/forum/63-gm-diesel-engines/21-6-5l-diesel-engine/268296-ops-relay-mod-install-1992-1995-obdi-trucks.html. Or you will burn out the OPS very, very, very fast. Trust me on this. Even with the AC Delco D1808A OPS, I strongly recommend that you do the OPS Relay Mod.

The after market OPS' simply do not have the capability to carry the lift pump electrical load. Installing the mod takes the electrical load away from the OPS. The OPS just triggers the relay.

See post #2 in this link for a .pdf file that has a wiring diagram for the OPS Relay Mod: http://www.dieselplace.com/forum/63-gm-diesel-engines/21-6-5l-diesel-engine/598490-lift-pump-not-working-wtf.html
 

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Discussion Starter #19
I just crawled under the truck and had my wife turn the key on while I physically held the lift pump...nothing. I then jumped the relay under the hood and the lift pump started running. So which part is bad the OPS or the relay?
 

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Discussion Starter #20
I just replaced the ops and the relay but the pump still don't run. If I jump the relay plug the pump works...what's going on here?
 
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