'87 V10 (350TBI) cutting out intermittently

[RecklessWOT]

Not sure if this is the right place to post, if not, someone please direct me to the right place


So I've got an 87 Suburban that's been acting like ****. It's been cutting out a lot on me lately (getting worse by the day). I've been trying to limit how much I drive it lately but the wifey is going away to a family wedding out west next week so I will be forced to drive the Chevy to work and back all week (70 miles round trip through the white mountains) and I will not have her car to use while she's gone.

The problem is intermittent and random, sometimes it will run fine all day long unless I get into it going up a big hill or passing a car (basically any time I demand a lot of fuel) and other times it will stall and idle rough and barely take off from a stop no matter how lightly I hit the gas. Not a simple sputter either, it completely flat out dies then comes back every two seconds. I could leave my foot to the floor and it will just hop up and down. Weird part is that I don't even get a check engine light through all of this. I know the light works because it turns on at startup as it should and turns back on when the truck stalls, but never saves any codes. It only gives me a code 12 over and over as if everything's fine. One time, and only once, I managed to pull a code 42 out of it when it was running exceptionally bad and I beat the **** out of it on purpose just trying to get it to throw any code at all. The code 42 led me to replace the ignition module on the distributor yesterday, but still no change. A month or two ago (before any of this started happening) I did a full tune-up (plugs, wires, cap, rotor) which was long past due. It was fine for a few weeks but started having this problem later on. Between then and the start of the problem it did overheat once the day my fan clutch died, I was idling on the side of the road on a 90 degree day for about 5 minutes and when I got back in it was pinned at the top of the temp gauge. All seemed fine once it cooled down and I put the new fan on, but I started noticing this issue a couple within a week or two from that (I doubt they're even related but what else do I have to speculate on?) At first it was only showing itself during heavy acceleration at the top of first gear it would cough a little bit. That led me to change the fuel filter (which ended up being perfectly fine anyway, but I initially thought it may have been clogged the way it was acting). It stayed the same for a while until last weekend when I was down in CT visiting friends and it fell flat on its face pulling out of a parking lot and ran like crap all the way back to where I was going (stalling, idling rough, backfiring). It was fine for the rest of the day till I tried to drive home to NH. I barely made it up all the hills on 91 going through VT. Ran fine on flat ground and down hills, but any time I needed extra fuel it would just cut out.

I really have no idea what the problem could be. Bad ECM maybe? I don't understand why it wouldn't at least throw an OBD code if it were an EFI issue or something of that nature.

Has anyone experienced something similar or know of a reason why this would happen? Other than this the truck is in perfect mechanical shape. I'd really like to get it back to being as reliable as it was before now

 

[chengny]

I would look at the EST system again (the module is only a small part of the EST group). A fault in the electronic spark timing is what sets code 42

According to GM there are a couple of conditions - related to 42 - that can cause poor performance and yet do not always set the DTC.

Inspect the external wiring, especially between the distributor and the ECM. The diagnostic doesn't require any special scanner or equipment. Read these sheets:

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[RecklessWOT]

Thank you, that is actually really helpful. I haven't had any time during the week to work on it, but will be looking into it today. Hopefully I can find the problem somewhat quickly, I hate wiring issues. My biggest enemy with vehicles. At the moment, just about everything I own has an electrical problem of some degree.