Need Help...Don't know what this issue is

[jdempsey]

Hello all,
Apologies if this is a repost of a previous thread, but I don't know what to classify this issue as.

I was driving home tonight when my 1987 GMC Suburban 2500 (6.2/TH400) acted as though it went into a limp home mode. It stalled a few times, but would restart, I checked the tranny fluid (good) and the oil (good) when I got home. I checked the tranny when I got home (truck still running) and the oil after I left it sit for a few minutes.

When I started it again, the engine seems to idle fine, but when driving, the truck was barely breaking 10 mph with the gas floored and the engine would surge as though it would get choked out them recover. I had to climb hills to get home and almost didn't make it. The weight of the truck going uphill almost stalled the engine.

I have recently replaced the vacuum pump. Not sure if that matters because the truck was running fine until this evening.

I am at a loss. Does anyone have a troubleshooting guide or ideas for isolating the problem?

Thank you for your help.

JD

[DmaxMaverick]

Welcome aboard!

I suggest replacing the fuel filter first. Don't worry about any other things, just yet. Most of the time, that's all it is. If this happened shortly after a fuel fill, suspect the fuel (gas).

[DmaxMaverick]

Replacing the fuel filter is not only the "almost always" cure for your symptoms, the process is a valuable tool toward diagnosing the problem if it isn't.

Also, if you haven't successfully changed a fuel filter yet, there's an easy process to change it without cranking for 15 minutes.

Engine off. Remove the air cleaner assy, top and bottom (it's in the way, but later you may not have to once you figure out where the connector is, also a good time for a thorough cleaning). Replace the fuel filter (do not try to pre-fill). Disconnect the pink wire from the injection pump (forward-most wire on top of the pump). Route the filter assy. bleeder tube (if it has one, otherwise makes a mess) to a container, and open the top bleeder. Crank for 10 seconds. Check the container for a couple ounces of fuel. Crank in 10 second intervals until 10 seconds produces more than a couple ounces. If that never happens, suspect the fuel lift pump, restriction, or a leak. Once the filter is bled, close the bleeder and remove the container. Replace the injection pump pink wire. Replace the air filter assy, and whatever else you may have moved/removed. It should start nearly normal. It may stutter or rev a bit, but that's just the little bit of air in the system finding its way out.