Suspected TBI or fuel system problems, 89 C3500 dually dump

[Chrus]

Hey all,

New to the forums. Former Ford Ranger junkie who just bought a 1989 Chevy C3500 Cheyenne dually dump. 350 gas motor, 4 speed stick.

I love this truck, but I'm having some issues and unfortunately I know very little about these older Chevy trucks.

Here's what's going on:

It drove beautifully home from where I bought it, ~40 minute drive. Nothing funky at all.

Gas tank very near empty, so two days after getting it home I put 12 gallons or so in, after not driving it since getting it home.

Drove great to get gas, but on the way home it choked up and lost power and started running like poop and wanted to quit real bad unless I gave it a LOT of throttle. It felt like I was running it out of gas, which is not possible, given how much I put in and how far I went.

Now it doesn't really want to stay running, and generally just runs poorly. Still has no power and wants to stall out. I had it running for a few minutes in the garage earlier today, and it kept revving up and down on its own, very much how my old ranger used to act when the Idle Air Control was bad.

Background on this truck: the owner before me had it three years and it literally sat in his yard during that time and he put less than 2 miles on it.

It had an electric plow frame that had an electric fire once and a lot of the wiring was replaced by former owner, very clean looking work.

Prior to him owning it, it just sat in a parking lot year round and plowed said lot in the winter.

Do you guys have any immediate thoughts on what could be wrong?

I plan on replacing the fuel lines from the tank to the engine bay, plus the filter, because the lines are awfully corroded and wet in spots, I doubt that's related but I'm sure its not doing the truck any favors. I thought maybe the filter got plugged and its fuel starved but I'm starting to think there's something wrong with the TBI.

Any help you can offer is greatly appreciated...

 

[77Impala]

Change the fuel filter for sure and hope that helps.
Check for vacuum leaks as well.
Since it runs with throttle applied the fuel pump should be fine, but leads me back to questioning a vacuum leak.
You can look down the throttle body with the truck running (very carefully and at your own risk) to see how the injectors appear to be firing the fuel into the air horn of the throttle body.
It is possible that the ignition control module under the distributor cap may have gone bad.

Hope this helps.

 

[Justin S]

I second the fuel filter change, especially if it sat around for a while without much gas, I bet you stirred it all up good when putting gas in, and clogged the filter. I'd start with that and the lines like you mentioned and see how that does.

 

[Ironhead]

If a truck sits for an extended period of time with only a small amount of gasoline in the tank, condensation will cause rust to form on the inside walls of the tank. Now, you drive it to the filling station, add gasoline, and the gas disturbs the rust on the walls of the tank, and some of it runs through the lines. It can plug the filter, and play havoc with injector nozzles. So, first thing is to remove the filter, as mentioned above. Not sure if our trucks will tolerate this, but on the older vehicles I've owned, the next step is to use compressed air to blow out the line from the filter to the tank.

I'm not sure if there's a screen in the fuel tank, but in an extreme case, you might have to remove the tank, pump, etc, and thoroughly clean them out. Old fashioned radiator shops used to boil out tanks, and you can then "slosh" the inside of the tank with a compound sold for air craft fuel tanks. Sloshing compound is what you ask for.

I hope in your case, you do not have to resort to such a drastic plan, so I'd do things one at a time, starting with the filter.

 

[90halfton]

Possible got bad gas too. Definitely drain whatever is in tank.

 

[cplanubis]

You have a dump bed take 5 mins and pull the fuel pump out and take a look at the inside of the tank and if need be clean the pickup strainer

Sent from my XT1080 using Tapatalk

 

[Chrus]

Thanks for all the advice guys.

I was in a rush to get using this truck but I just don't see it happening for a while.

I replaced most of the lines; from the braided stainless lines to the filter, and back from the new filter to where they were in decent shape coming off the tank. Would have loved to gone all the way back to the tank, and will eventually, but that was my quick fix attempt.

I didn't replace the vapor line but that shouldn't be THAT critical to the engines performance should it?

After replacing the lines and filter, I got it to the point where it would stay running but it would get to just about quitting and come back, and just keep doing that. It usually didn't quit but would sometimes.

It was also starting to misfire or skip and generally just not running great... new plugs, wires, distributor cap + rotor, not much difference. Old plugs were bit gunky, but not worn down too much at the electrode

Replaced the IAC and the ICM (it was so cheap to do I didn't even see a point testing the old ones and they are probably original anyway)

I haven't had a second set of eyes/hands to help me out, but it seems like the injectors are spraying a good amount and pretty even, based on the amount of fuel I see there

I took the tbi apart to clean it and realized it ought to get a new gasket set, that's on the way. Would old crappy gaskets cause/count as a vacuum leak? I have to imagine they need to be providing a good seal. Found a great deal on an injector set, that's also on the way.

Replacing the MAP sensor because I hear they can be faulty and it was again, so cheap to do.

Realized I left the map disconnected last time I went to start it and it wouldn't start anymore, even after I reconnected it. Any thoughts on that? Just kept cranking. Seemed to have plenty of fuel in the TBI.

Feeling pretty frustrated. I'll update as I work on it, I really appreciate all the advice. I'm 22 and I don't know diddly about these trucks and would really like to learn.

What/where am I looking at for vaccuum leaks? How do you go about testing for leaks?

 

[77Impala]

How strong is the spark to the plugs? A weak coil possible since you have replaced plugs, wires, cap, rotor, and the ICM.

Also check/replace the EGR, if dirty/clogged it can cause your issue. And check the where it mounts for carbon build up.

Does your truck have the smog pump? Mine does and it had a disconnected hose from it to the air cleaner. When I reattached that hose I found that the check engine light would come on but there were no codes. Disconnected the line from the air cleaner housing and no more problems.

Simple way to check for vacuum leaks is to look at all the rubber hoses that connect to the TBI and also the intake manifold and if you see any cracks or other issues then replace them. If you have a leak in the vacuum brake booster you should either hear the hissing sound and/or notice that it is harder to push the brakes.

Other wise get a vacuum gauge from a auto parts store and measure the vacuum on the lines. And if you get one with a vacuum pump you could also check the parts such as the EGR to be sure it opens and holds vacuum.

Lastly your ECM (Engine Control Module/computer) could be faulty and need replaced. I would check all other options before replacing the ECM. Cost for them are less than $150.00 usually.