Stalling problem - NOT pmd/lift pump/ops switch

[97-6.5TD-F]

Well my 97 has the grays coming out in full force, lol. The same stalling problem has come back. I will tell the details before I mention what parts i changed and how many times.

Stalls out when hot, particually bad when worked hard towing, etc. Lift pump doesent run at all once stalled. The lift pump relay clicks on and off rapidly when the key is turned on, and it seems the engine light flashes at the same pace as the relay clicks. The service throttle light dosent illuminate when the key is turned on, that is until it is ready to start. As soon as the service throttle light comes back on, it fires right up, lift pump starts going, etc.

I checked wiring schematics and the pcm controls the lift pump relay, service throttle light and the check engine light. Could this be the cause of this nightmare of mine?

I have replaced the pmd twice and have a brand new Dtech waiting to go on. third lift pump, as the first time I changed it the problem went away for about a month,new lift pump relay, new oil pressure sender, lower mileage inj pump, rebuilt engine last june.

Any help on this would be very much appreciated as like I mentioned eariler, my old truck has got the stress level though the roof not being able to count on her for any kind of road trip :o.

Heres some details of the truck, 97 K1500; 230k miles; F pcm with egr/maf delete; dsg gear drive/phaser; stock otherwise.

[JohnC]

Sounds like an electrical issue. Battery connections, connections at the starter, ground connections (especially at the rear of the passenger's side cylinder head), ignition switch...

[Bnave95]

Some times changing parts you could be taking care of Elect. issues.
Your truck sounds like it is having Elect. issue. Now it's time to clean things up.
Fuse box,connectors, Batterys. Have you heard of the Dr Lee battery post up grades?
This should be a Sticky,though it has stuck with me.

[Warren96]

I have been working in electronics for over 40 years, that being said, what you are describing is a loose connection. Find someone who can sit in the drivers seat and watch to see if the dash lights blink while you move around the truck. GENTLY move different wiring connectors (under the hood and behind the glove box where all the 'puter connections are). Do this with the engine OFF, that way you won't get burnt on hot engine parts. Occasionaly look up at your helper to make sure she hasn't dozed off, When the lights blink you are getting close. Take your time! It takes an EXTREME amount of patience to find an intermitant. The reason you gently touch the wiring is that you may put a slight tension on the loose part and cause it to start working again but only temporarily.Then tomorow, next week or next month it will come back to bite you on the butt. These are some of the things that have worked for me, I come across intermitent electronics at least 2 or three times a week. One question; Have you cleaned and sealed the connection on the black wires that bolt to the intake manifold on the pass. side, like John C told you ? Keep us posted, happy hunting, and good luck.

[Warren96]

Any codes?

[97-6.5TD-F]

No codes, history or current. Grounds on the engine block have 0 ohms resistance, same with every other ground i could find.

It has been good for about a week now with no stalls, I wonder what the chances are the pcm is the cause? It seems plausible since the three things that it does when it stalls and then dosent start for half an hour ( lift pump relay, cel and sts lights) are all controlled by the pcm.

[twaddle]

Hi there,
My 96 Suburban had the dreaded Intermittent Stalling pretty much exactly as you are getting.
Back when I bought it in 2001 it would stall once then wouldn't do it for several months. Despite increased number of ground cables (which did seem to help a little) , cleaning any multiplug I could lay my hands on and the usual new PMD (even tried the dreaded Sol-D with it's cold morning problems) the problem remained (albeit very intermittent). As time went on the stalling became more frequent, every few weeks then down to several times a day. It also, on occasions, refused to fire up in the mornings.
I noticed that when the beast refused to fire up certain dash lights and the glow plug light (wait to start) would not illuminate. This would happen either cold just firing up or after stalling at working temperature. I was sure the PCM was at fault but as you are finding, no codes were present.
A DP member from Arizona was selling a second hand Heath PCM which I bought and shipped out to Scotland just in case.

About 3 weeks after receiving the Heath PCM my Suburban stalled and this time would not fire up. Unfortunately I did not have the Spare PCM with me so I was towed back home where I installed the spare PCM. The engine fired up straight away. Put the original back on and it would not fire up. back on with the s/h Heath unit and it hasn't stalled since (touching wood quickly).

Does your "wait to start" light not work when the engine won't fire up?

I suspect you have a PCM on the way out.

Good luck and I hope you get it sorted out soon, I know how wearying it is.

Best wishes

Jim
Formerly Biggar, Scotland
Now residing in Stony Plain, Alberta

[97-6.5TD-F]

No my wait light doesent come on because it only does it when the engine is hot. It always starts cold and only stalls once warmed right up.

[Robyn]

With all the items you have had your hands on it very well may be that the ECM is having issues.

A failing ECM will not always set a code either.

best

Robyn

[twaddle]

Hi there,
The WTS (wait to start light should still operate when the engine is warm, it just won't stay on as long as when the engine is cold.

If I was you I would try and get a new or good second hand PCM, even borrow one to use and see if it cures your truck.
With no codes it is the only thing that you can do. Is there any other members in your area that would have a spare or could loan you one for a short while?
Believe me I know the frustration and helplessness especially when you are a qualified mechanic but with the symptoms you are having and what you done so far your situation is almost identical to what I was getting.

Good luck and let us know how you are getting on with the problem.

Jim
From Wintery Alberta (Back down to windchill of -17)

[More Power]

When it's acting up, check the various ignition circuits. Ignition switches do wear out over time...

Jim