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Discussion Starter #1
It has been a while since I have been on this forum but I need some help as I have tried just about everything I know or have read to do and can't figure my issue out.

I have a 1994 6.5 Turbo diesel that will not start. Here is the best I can do to fill you in on what I have tried and done. I have checked all ground wires and made sure they are good. I have replaced PMD box with three different ones, including one that I know was working in another 6.5 diesel. I have changed Oil sensor switch and glow plug relay. New batteries and new starter. I have checked all fuses and they all check out. My problem is that when I turn key, my glow plug light will come on for about 1 or 2 seconds and go off. I can hear relay click. If I turn the key off and try the cycle again, the glow plug only flickers and the relay will click. If I try starting the vehicle, no fire and no smoke. I hear no lift pump starting either. I have jumped the lift pump relay and the lift pump starts pumping and I have fuel to the fuel pump and filter. No air bubbles. The problem seems to me to be the fact that my glow plugs won't stay on and there is no signal to the fuel pump to start working. I have tried unhooking temperature sensor to indicate cold motor so glow plugs will run full heating cycle but nothing changes, glow plug light just flickers and relay clicks. I have tested PMD power and it is receiving power when cranking engine. This all appears to be an electrical issue. Maybe ECM but I just don't know. I have also check fuel shutoff solenoid on pump and when applied direct power to the solenoid, it works just fine. Fuel injectors have less than 10,000 miles on them and the glow plugs were just replaced with brand new ones. When I check glow plugs, they do receive power for the 2 seconds the light comes on but when the glow plug light just flickers in the cab, no power to glow plugs. It all appears that something has locked the entire system down, like a security issue but why and how. Just my opinion. Very frustrating. Can anyone please help.
 

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When you interrupt the glow plug circuit, the ECM needs to "relearn" and will command the glow relay for 1-2 seconds for a few IGN key cycles and then go back to the normal 5-10 sec relay activation.

Did you use AC Delco brand when you replaced the OPS and Glow Relay parts?
Aftermarket electrical parts do not work well in a 6.5L

Did you make sure the PMD has a resistor installed on the pins?
The resistor is an important part of the PMD.

Checked for any DTC's?
 
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Try pulling the driver bank glow plug leads... take a rag or paper towel and clean the glow plug connection tabs. Inspect the connectors themselves... clean if necessary...

sometimes the connectors bend a little bit over time as well. Take some pliers or a screwdriver and bend the harness connector tabs back down ****just a little*** so when you connect them back on their good and tight.

I had this problem for a while when I first got my 94.

Works great ever since.

:thumb:

Its worth a shot at it.. I say the driver bank because the passenger bank is much more difficult to access. Though it's not so bad getting to #6 and 8. 2 and 4 are no fun at all. To me at least. Driver side bank being 1,3,5 &7.

Anyway if that dosent work it's likely the controller or relay...


As for the lift pump... the lift pump circuit runs on the oil pressure sensor. Search for "94 95 lp ops mod" and do that... the OEM setup causes premature lp failure.

Maybe okdually can provide the link to it...

:thumb:
 

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When you did ground check. Did you check the ground wires on the right rear intake manifold bolt? It is the main ground for the GP relay and PCM.
 
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Open as many fuel injector line nuts as you can reach, then crank it. See if any fuel is exiting the IP.
TRIPLE CHECK THE GROUND WIRES ON THE REAR INTAKE MANIFOLD BOLT.

Also, pull the fuel filter, suck out all the fuel from the bowl, and visually inspect the screen at the bottom of the center pole.
 
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Check for kink fuel hoses?
Burn out cables/wires?
 

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Discussion Starter #7
First off, I understand the ECM has to relearn but I can sit and turn the ignition on and off for 10 minutes and nothing changes. I literally did that one evening when I found just what you said that it takes a bit for the ECM to relearn but nothing changed. Just a flicker of the light and click of the relay.

Yes, I have checked the ground literally 10 times on the intake manifold at the rear of the engine. I even took the stud out of the intake manifold and shined all that up as well. I replaced ends on the ground as I thought that might be an issue as well. No change.

Also, I am sad to say that I have not used AC Delco parts on the relay and OPS sensor. Got them at a major parts store, but I won't name names. As far as a resistor goes, this truck never had one since I have owned it. I replaced my first PMD box about 4 years ago and that one did not have a resistor in it either. I have wondered if putting one in would help but I have read multiple forms that say you need one and then a bunch of forums that say you don't need one on 1994 model. Confused but it has ran for over ten years since I have owned it without a resistor so I just have not gone down that road.

I will try unplugging the glow plug bank on drivers side and see what happens. It's worth a try. I have read about the OPS modification kit but I haven't done this yet because I figured if a new OPS didn't fix my starting issue I would wait till I got the truck running first.
 

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Make sure the 2- 18ga. ground wires at the rear of the pass. head are good, along with the 10ga. ground.
Try unplugging the OPS and see if things change.
Make sure all the fusible links are good at the buss bar, especially the small gauge links.
 

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Loosen the water drain, short the pump fuse holder to the power stud on the firewall.
Verify you have fuel flowing out the drain hose.
Then loosen the fuel line feeding the top of the IP, put it in a soda bottle and short the fuse again, verify the bottle fills quickly.
If that is good, no air bubbles, loosen the injector lines and crank till you see fuel.

No fuel? It will never start.
 

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Discussion Starter #12
Ok, I am back on this project and still no resolve. I have replaced and checked everything I can find. I just replaced the PMD box again and I put brand new glow plug wire harness, new glow plug relay and new glow plugs, still nothing. The problem I can't seem to get by is that I am unable to get the glow plug cycle to engage. The glow plug light and relay just flicker/click once for every key turn but no full cycle. What is causing the system to abort the glow plug cycle? It's like something is not letting the cycle take place hence no fire. I tested the wiring at the PMD box and it all checks out. The computer is communicating with PMD box but why doesn't the glow plug cycle? Please give me new direction. From my previous posts, I have checked ground wires repeatedly so I am pretty sure they are good. Please Help. Very frustrated and tired of sinking money into this truck with no results.
 

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Check the ORANGE wire at the OPS conn. for 12v. batt.
It should be hot all the time.
Unplug the fuel heater and WIF sensor on the FFM until you get it running.
Make sure the ECM-I fuse has 12v. with key on.
 

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Ok, I am back on this project and still no resolve. I have replaced and checked everything I can find. I just replaced the PMD box again and I put brand new glow plug wire harness, new glow plug relay and new glow plugs, still nothing. The problem I can't seem to get by is that I am unable to get the glow plug cycle to engage. The glow plug light and relay just flicker/click once for every key turn but no full cycle. What is causing the system to abort the glow plug cycle? It's like something is not letting the cycle take place hence no fire. I tested the wiring at the PMD box and it all checks out. The computer is communicating with PMD box but why doesn't the glow plug cycle? Please give me new direction. From my previous posts, I have checked ground wires repeatedly so I am pretty sure they are good. Please Help. Very frustrated and tired of sinking money into this truck with no results.
Any time you interrupt the glow circuit the PCM will go into a relearn and only give you short glow cycles of 1-2 seconds for approximately 20 IGN key start cycles an then the PCM will go back to normal glow times
 

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Check the fuses?
I agree with Redneck on the Ignition Switch?
I think Glagulator is telling you how to check it properly.
 

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Have you tried swapping out the PMD cable? I didn't see that mentioned but I may have missed it. Also is your CPS working?
 

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Discussion Starter #17
Did and tried everything that Gladiator talked about. Tested Orange wire on OPS, which is brand new, and it has 12 v with key on. Unplugged fuel heater and WTF and still no glow plug cycle, just flicker/click. I checked all fuses in the fuse box and tested them and they all checked out ok. Even replaced ECM and glow plug fuses with brand news. I also want to mention that the CPS was replaced. I also made sure that I got past the 20+ key strokes to hopefully allow the system to relearn what it needs to and still no glow plug cycle. Any other ideas? What else could be stopping the cycle or no start alert? That is what it seems to me is the main issue is that something else is malfunctioned and the ECM has locked down the start procedures from taking place. Let me know. Thanks.
 

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Is the LP pumping when you put 12V direct voltage? Let's start from there.
Then, see if you can bleed the air?
After that keeps running, you need to start cranking.
It may take a while so batteries need to be load tested one at a time.
Saying that the battery is very young is NOT a test.
The fact is, part store can sell DOA batteries also.
 

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The GPR is controlled by the PCM.
The PCM has 2ea. 12v. power feeds.
One is the ORANGE WIRE that feeds the LP and the PCM and is 12v. all the time and is what keeps the memory alive. It comes from the buss bar and has a fusible link. Check it.
When that feed is interrupted the PCM goes into re-learn, you get a very quick cycling of the GPR relay. That normally only lasts until the key is turned off then back on.
The other PCM 12v. feed is the GAUGES FUSE (PINK/BLK WIRE) and is hot when key is on.
It turns the PCM and some other things on.
Just FYI, some of the testing I suggest is checking circuits and may not seem to have anything to do with the problem. For instance, checking the ORN wire at the OPS, just a convenient place to see if the LP/PCM circuit has power, not checking the OPS.
The WIF and fuel heater are also on the GAUGES circuit and can cause problems, just leave them unplugged until you find the problem. They will not effect starting.
I would test the GPR control function next.
Use a 12v. test light, not a voltmeter or multi-meter. It will add some load that can trigger an intermittent connection where a meter will not.
Turn key on, does the PINK wire on the GPR conn. have 12v.?
Weak voltage will cause the test light to dim. Check the test light on a battery to see what 12v. looks like.
Does the test light show voltage between the PINK and the BLACK wires of the GPR conn.?
If so, with key on, apply 12v. to the yellow wire.
Does the GPR activate?
Have you inspected the fusible link (F.L.) from the battery to the buss bar?
And the F.L. from the buss bar to the GPR?
The WTS light gets the same voltage as the glow plugs so if it is flickering then the GP's are doing the same thing, or your dash ground (just above the DLC) needs work.
BTW, the GLOW fuse is there to protect the gauge cluster and PCM from the glow plug voltage signal. It does not feed power to the GPR and is only hot when the GP's are glowing.
If the GLOW fuse is removed the WTS light will not work and the PCM will not know what the GPR is doing.
There are many things that could be causing your problem.
The only way to figure it out is to test and verify what is not the problem.
 

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Discussion Starter #20
Gladiator, that all sounds good. I have done alot of this already but not how you laid it out. I will follow these tomorrow and see what happens. Also wanted to mention, not sure if it is relevant at this time but I did jump the OBD connection to see what DTC codes might appear. The only code in the system is DTC 14 which is Engine Coolant Temp Sensor too low. I went a head and replaced both temperature sensors today just to make sure. Still getting same results. I will keep you post tomororw what I find when I run through all the circuit testing. Also wanted to mention that the lift pump does work just fine when applying 12v to it. Thank you and hopefully this old beast will be running again.
 
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