I resolved myself to asking you guys...


The dealer changed the lift pump on my 95 TDiesel 6 months ago.


As I was driving this week the truck got the same symptom, the lift pump stopped (I guess?) and the truck lost half of it's power. I could barely go to 55 mph. I pulled over and restart, went fine all the way home.


The lift pump is on warranty but the dealer won't honor it unless the code is present, on the 1995's (OBD1) the codes don't stick.


Does I assume it right when I say the lift pump is bad ?


Could it be the OPS ?


Does the PCM keep a trace of error codes ?


Thanks again, great forum.


Daniel

On a 95 you can jump pin A to B on the ALDL connector and count the flashes of the SES light. Sounds like you went into limp mode. no advance or boost or fuel till you restarted.

dan, that is not a lift pump problem. lift pump would shut the engine down completely.


injector pump is controled by the pmd[pump mounted driver] , the black box on the side of the injector pump.


300.00


change that controller, bingo all fixedEdited by: kjanx

It could be the low res lost track of the data disk long enough for limp mode. Cloudy fuel could cause that. PMD issues tend to involve stalling, cruise control not woking, not saying it's not possible.

If the truck did go into limp mode, SES would light up and you would have history code(s) telling you what the computer didn't like. PMD problem will not cause this, optic sensor would be constant. Boost sensor out of range is the most common one. Wastegate solenoid stuck in open position, full vacuum to wastegate, turbo over boosts, ECM sees this and kicks you into limp mode.


My advice, change the $20 Wastegate Actuator switch.Edited by: Texas Diesel Guy

A little note, that lift pump will not cause engine to stop. The OPS may keep the lift pump from running, but it's not to stop the engine, as some may think. The OPS shuts down the lift pump in an accident upon loss of oil pressure to keep fuel from pumping everywhere. Engines will continue to run without lift pumps running, just not very well.

I bet it's the OPS. My 95 did the EXACT same thing you described when my OPS went out last winter.


Jump the pins on the fuel pump relay to check OPS. Someone here can explain how, or I'm sure you can find the proceedure by searching the forums. It's FREE, as in it costs your NOTHING, to check it. It takes five minutes to learn how and only two minutes to do it.


Please don't just run out and buy a new PMD!http://www.dieselplace.com/forum/smileys/smiley5.gif

Thanks for the responses.


I was leaning toward the OPS, I'll try and find the link to verify the switch or simply replace it and see how it goes.


I just checked under the hood, very well hidden. Any tips on how to replace it.


Do I have to remove the filter bowl ?


What kind of deep socket is needed ?


Thanks again.

Get an OPS tool (socket). It runs about $10 at most parts stores. On a 95 is it located in the valley between the filter and the intake?

I was able to get at mine by removing the two bolts that hold the filter in place and then pushing it out of the way. Edited by: w_huisman

I bought my OPS and socket, i'll get to it this weekend.


I'll keep you posted.


Thanks again.


Daniel

Update.....


I changed the OPS switch....with no effect. I am just returning from a 200 mlies trip and the truck did it again http://www.dieselplace.com/forum/smileys/smiley7.gif.


The truck failed on our way back. Sounds like he went on limp mode like quantum mechanic said. This time, instead of stopping and restarting the truck and clearing the code, I went straight home, took a wire and jump pin A to B on the ALDL connector.


The count came in - ------- has in 1 7.


For the first time, the SES light came even after hard restart. The code was still 1 blink, a pause and 7 others.


The situation is degenarating, I surely don't like the look of this.


Thanks for your input.

High resolution circuit fault code, looking like IP problem TDG can you shed more light on that code.


Dan you have changed the fuel filt correct??


How many miles on the IP


Have you connected a gauge to the fuel filt drain open while running, gauge should show 4-6 psi for functioning lift pump could still have a bad lift pump so check with gauge, if checks okay at idle run with the gauge installed, should maintain 4 psi at cruise, may dip to 1.5 then recover back to 4 if on hard acceleration.


Hi res code not looking good though.

If your able to restart it and clear it, it could be a wiring/connection problem or a bad ground. The harness begins at the IP goes to the big connectors at the rear of the engine where the fuel filter is and then to the left where the heater hoses go into the firewall.

To turbine Doc;


-the filter has one month (600 miles).


- the IP, 60k.


-and, yes fuel was coming out of the filter vent.


To QM;


I'll check the connections, but I doubt they are the cause of all this.


In the mean time I checked the prices for parts;


-PMD 500$can


-IP 2000$can http://www.dieselplace.com/forum/smileys/smiley18.gif


Thanks for the advice.

The vehicle is not stalling, just kicking into limp mode intermittently right? PMD won't fix your optic sensor codes, and if you don't have a stalling concern won't do you any good to change it.


Need to rule out air in fuel first of all, see about buying a clear line to run on the return fitting from the pump, start the truck and get someone rev her up for you and make sure there's no air bubbles present. If there are, need to cure that first, if not, most likely optic sensor is taking a dive on you. If there's air, it can only be getting in at or before the lift pump where there is a partial vacuum, beyond the lift pump you can only have a leak because the fuel is under pressure.


You can get an IP with new updated optic sensor and PMD cheaper than that.

Yesterday, for the first time the vehicle did stall.


It started afterward (not with ease) but in limp mode and ran very rough all the way home.


That's when I took a wire and got a code 17.


I'll rule out the bubbles first....


Thanks for your input TDG.

No bubbles in the pump return.


However, I did learn from a service tech that the GM warranty on the Stanadyne electronic injection pumps was extended to 11 years or 193000 km.


I took the truck to the dealer this morning. They just called to confirm that the IP is at fault. They are waiting for GM's approval to change it.


Thanks to all, I have learned a great deal.


I'll keep you posted