1988 R20 Suburban won't stay running

[dwntwn]

I haven't had this vehicle too long—it needed a few things like tires and battery but its a pretty clean, well maintained vehicle. In the first week I replaced the coil, plugs, wires, cap and rotor and its ran great.

Last Friday after a 75 mile trip out of town it wouldn't start without a lot cranking, its never done that. When it started it wouldn't stay running for more than 10-15 seconds. The injectors are pumping fuel while it runs, then it cuts off.

I replaced the fuel filter and fuel pump (Delphi). No change.

Confirmed the grounds at the fuel pump, water neck, pulled the starter to inspect all the wires where they are near heat, no breaks.

I replaced the oil switch and sender thinking possibly the switch wasn't sending the pressure reading to the ECM, no change.

I have tried the paperclip trick but was unable to retrieve codes. Not sure why that is. I replaced the ECM thinking that was the problem, but it still won't stay running and is hard to crank.

I just replaced the IAC, which seemed to make a difference at first—the idle was higher but the engine still cuts off after running a few seconds.

Not sure what to think—this truck ran so good and now it won't, its got me convinced it HAS to be something simple (its got 3/4 of a tank of new gas) but I'm stumped.

[oltronj]

I am by no means an expert but it sounds like the ECM isnt getting a signal that the engine is running and then shuts it down. Not sure if the ECM is supposed to get an RPM signal from the distributor but I would start there. Hope this helps.

[Ski-me]

Totally guessing too, but my Blazer 89' would run no problem and then for no apparent reason, not start. Just crank and crank. Replaced entire distributor and has been reliable ever since.

You've thrown a lot of parts at it too (albeit, probably necessary maintenance items).

When it does run, is it smooth or does it stumble? Injector spray look good and constant up to the stall? Does it stall and it appears that the injectors stopped (resulting in the stall) or do they spray "into" the stall?

[dwntwn]

Thanks for the replies you guys! I got super busy with the holiday and finally had a minute to update:

I was unable to retrieve codes or keep it running because the 10A ECM fuse was blown. How long, I can't be sure but I am guessing it was the original issue (not fuel delivery)

Once the fuse was replaced the Suburban started and ran normally, but after running for about 40 minutes began to stumble and idle rough. The glove box was out so the ECM (which had been replaced) was accessible. Grabbing hold of the wires, gently grabbing hold of the ECM and slightly twisting the box evened out the idle. The ECM was exchanged, so far the Suburban is running great.

Looking back on it and taking guess, it was probably an ECM issue all along. Either way, I'll leave a reply in case someone goes through a similar situation.