Late 80's/ Early 90's GM TBI - Thoughts? Known Issues?

A couple of issues I just noticed today:

At idle, sitting at a stop with foot on the brake in gear, the idle sometimes seems high, and other times seems what I would call normal. Idle is smooth and even regardless, though.

I haven't really driven the engine hard, but today for the first time I decided to try a WOT from a stop. I didn't mash the gas, but rolled into it quickly. The engine bogged, to the point that I thought it had stalled, but then caught and the truck accelerated fine.

The exhaust smells a bit rich at idle, but I haven't put an oxygen sensor on it yet to take a reading.

Tested it a few more times last night. From a rolling (perhaps 15 mph or so) start, and flooring it, it accelerates fine, but from a dead stop, a fast WOT results in bogging. No other driveability issues, though. This weekend I may check the injector spray pattern and see if the injectors are worn, and check fuel pump pressure. When I changed the plugs, the old ones didn't look excessively sooty or burned, so the mixture is at least in the right ballpark.

Also check for vacuum leaks and egr issues.

When you did plugs, did you look at cap and rotor? What gap on plugs? What is base timing with the esc wire disconnected? And light?

One reliability issue that I haven't heard mentioned here is the fuel pumps. I probably replaced fuel pumps as much as anything on the tbi's. Regular replacement of the fuel filter helps to make it live a little longer. If you get stuck with a cranks but no fire situation, whack the bottom om of the fuel tank while someone cranks the engine. That will usually get the pump going and it will get you home. I think if I was very concerned with it letting me down I would put a new quality distributor in, and keep the old one in the truck. If I recall all you need to change it is a screwdriver and one wrench. Everything else in this thread is true, they are more or less unremarkable at everything, but they pretty much run forever, and when it doesn't parts are cheap and available, new or used. Rust kills these long before anything else does.

Mine always seems to run rich as well, at least until I've driven it for a bit. The ecm is only something like 9600 baud, and it only samples the o2 sensor every second or so, so it takes a few runs through the gears for it to find itself. I've also had similar idle issues, especially when cold. My ICV valve was very gummed up, so that may be worth checking. I think it's partially just how it's calibrated.

I've done the ultimate mods - they make a big difference, especially raising the injector pod.

Check your fuel pressure. They're all over the place from the factory. Also, make sure the throttle shaft bushings aren't completely worn out. They just ride in the aluminum body, and make a big vacuum leak when they go.

Did plugs/wires/cap/rotor with good quality AC Delco stuff. Forget what I set the gap to, but it was whatever I researched and found as factory spec.

The Cruise doesn't work, and it may have a vacuum line to it, I'll check that. I think I had noticed a slight hiss from under the dash, it's on my list to track down.

I may have a manual for these engines around somewhere...need to see what the EGR system looks like.

Need to check base timing, too. I know these low compression pigs wake up if you feed them a little base advance, like 8 to 10 before.

And I do want to change the fuel filter, it looks new-ish but no idea how much.

I've read the dizzies do "go bad", but not sure exactly what the failure mode is. Since the truck has 176k on it, and didn't come with any records, I've no idea what's ever been replaced. It generally runs/ drives pretty well, and has a VA inspection sticker from 2014, so I figure it has been somewhat reasonably maintained.

Luckily, the rust monster hasn't gotten to her too bad- everything structural is solid, and just a couple holes the size of a half-dollar on the driver's side lower quarter, behind the rear wheels. A couple of small places on the Rockers are soft, but still holding paint.

As I've said before, I've no plans to make a 250 hp bruiser out of this thing, I just need it to go up and down the road and get reasonable-for-its-size fuel economy and be reliable.

Check the timing with a light. Sometimes distributors go bad by wearing out their bushings and the timing gets weird and scattery.

tuna55 wrote: Check the timing with a light. Sometimes distributors go bad by wearing out their bushings and the timing gets weird and scattery.

Gotcha, thanks. Luckily, I have a light. Are these mechanical advance dizzies or is that all handled by the ECM? These have a knock sensor?

All handled by the ecm. Really, the hall effect or control module are the only two things in there that can go bad.

Make sure to disconnect the esc wire when you check timing.

Dusterbd13 wrote: All handled by the ecm. Really, the hall effect or control module are the only two things in there that can go bad. Make sure to disconnect the esc wire when you check timing.

Cool, good info, thank you. How do I ID the esc wire? Color? Only wire going to the dizzy? Location?

On yours, I don't know. Usually a brown wire near the distributor with a single inline weatherpack connector.

The esc connector will be outside the harness wrap/loom near the distributor. Here is a good picture of it, third post on page.

http://www.truckforum.org/forums/chevy-truck-forum/36789-timing-on-88-5-0-tbi.html

Cool, thanks for the pic. Perfect. I plan on doing the TBI mods to her, not so much for power per se but to get more power per gallon of gas.

your connector should be right by the brake booster.

I used to have a Safari van with the v6/TBI. Only issue I had with the fuel injection was the fuel pump. And whoever designed that truck without an access hole in the floor should be slapped around. But that is for a different thread.

had a 94 chevy van with tbi. drove it from 75k to 175k miles with routine maintenance, although did have to replace the starter a few times and alternator once.

even when i let it go at 175k i would not have hesitated to drive it cross country. easily one of the most reliable vehicles ive owned.

Just set the timing...the dizzy bolt required removing the coil and a vacuum tee to get loose...it may not have ever been touched. Anti-seized it up good when I put it back. Base timing (with ECM disconnected) was around 0. Just to check, when I reconnected the computer, at idle, it would crank it up to like 10. So I set it for 6 base...starting and idling is much improved.

In reply to Dusterbd13 :

You mentioned the ignition module, so, knowing something about the ignition module, maybe you can help me with a question about the TBI distributor.  I'm currently putting a TBI unit off of a 1995 Chevy pickup on my 1974 Chevy pickup.  I want to use an old style coil instead of the TBI coil.  Can this be done, and, if so how do you wire it?

Thx for any help.

Dan Brown

In reply to danbrown2 :

If i remember correctly, heavy pinks tied together on positive side of coil. This needs to be switched 12v. The white and other go to the negative side. 

This assumes small cap external cpil tbi distributor and me remembering right

I'm currently putting a TBI unit from a 1995 Chevy pickup on my 1974 Chevy pickup, and would like to use and old style (cylindrical) ignition coil instead of the TBI ignition coil.  Any body  familiar with doing this?  If so, how do  you wire it?

In reply to danbrown2 :

Not 100% sure on that particular mod, but if you start a thread about it you’ll likely get more/better advice. 

Why was the crossfire system considered a failure? I think it's a cool setup in theory. 

gearheadmb said:

Why was the crossfire system considered a failure? I think it's a cool setup in theory. 

1980's computing ability, terrible emissions heads, tiny cam and small throttle bodies. Basically the 80's are what happened to it. 

In reply to bobzilla :

I always thought two TBI units with progressive throttle linkage would be cool if you good enough at tuning to make it all work.

Since this zombie thread is reactivated, I'll post a link to the discussion with the fuel problems with my own 88 Silverado

Link