TBI troubleshooting

[chappys4life]

Everyone on here seems to love the tbi so help me fix mine before I swap to a carburetor. Have a 1990 GMC Jimmy 5.7 350. When driving the service engine soon light is flashing pretty quickly. If I am running down the road it seems ok but when I come to a stop and idle like at a light it cuts off. Typically I can crank the key a few times and I get lucky and it starts or have to disconnect the battery, reconnect, then it runs. When I try an pull a code currently there is nothing. It was throwing codes which led to the maintaince below but now no codes.

So far in the past year I have done
- carquest T1830 whole distributor
- ac delco plugs
- ac delco wires
- bosch o2 sensor
- ac delco map sensor
- wire sleeved a lot of the mess around the intake
- replace a lot of the vacuum hoses
- made 1/0 battery cables (ground from battery to block & battery to frame)
- optima red
- napa gold fuel filter
- delphi fuel pump

Is it worth changing the tps sensor? I tried finding a mechanic to look at it but no one wants to touch the tbi. I am at wits end.

 

[eodcoduto]

The first thing I would check would be the grounds from your battery to the engine and engine to the chassis and make sure they are clean and reading less than 2.5 ohms across faying surfaces.

Then check timing, fuel pressure, and the tbi temp sensor.

My intake gaskets were leaking, and my EGR was gummed up, once I cleaned all of that junk out of the valley and resealed it runs significantly better, and smoother.

I am not a fan of TBI, but it’s what I have and going to a carburetor is not going to net enough gains over a properly working system on a stock TBI engine.

 

[chappys4life]

Battery grounds are good. I made 1/0 battery cables. Have a 1/0 cable from the battery going straight to the motor and another 1/0 ground going from battery to the frame. I will check them with a meter but nice clean copper.

I can check timing and order a new temp sensor cause why not. maybe try and clean the egr too.

Oh i get no hp gains. Its more the pain in the but I have been dealing with this for just over a year and I am tired of tows. My other 2 daily drivers are carb and holy crap no issues like these. Also this motor is getting up there in milage so I have been considering a mild rebuild. Have a standard bore 350 sitting in my storage from a 76 corvette. Some nicer rods/pistons and slap some afr 195 heads on with a mild roller howards cam. Would be a nice replacement.

 

[BoondocK5]

First off, you need to find out what is causing that check engine light to flash.
When a check engine light is “on” that means the ECM saw a problem and has a stored code.
When the Check engine light is flashing, the ECM is seeing a problem currently.
Light flashing = problem currently exists.
You need to know what that problem is. Secondly, Stop throwing parts at it, hoping to get it.
Spend the money on a code scanner that can give you OBD2 information.
TBI systems are super basic, and not hard to comprehend. You just need a little information.

 

[CharlesC83]

It’s not the most fun. But I’d check the fuel pressure. Those diaphragms in the regulator can rip just a little.

Also spray brake clean around the intake and check for vacuum leaks. Look up how to check base timing on TBI. I have to look it up every time. But you can’t just throw a light on it like the carb rig.

Check for vacuum leaks on the actual TBI unit like the throttle blade and base. It sucks also but I’d do a compression check on the whole engine.

 

[‘89Jimmy]

Codes aside, kinda sounds like fuel to me. TBI is basically an electronic carburetor (a bit of a mental stretch) but I’ve read it likes about 12 psi fuel as opposed to the 4-5 psi carbs like. Definitely worth checking fuel pressure. Probably also worth taking a can of carb cleaner and cleaning it out real good (a rebuild in a can, if you will).

 

[Blue85]

I don't know if these guys are still in business, but having data goes a long way for troubleshooting: http://aldlcable.com/aldl.asp.

A lot of good suggestions have been given, but this one still seems to be a mystery:

Typically I can crank the key a few times and I get lucky and it starts or have to disconnect the battery,

I have heard of a few cases where something goes bad with the ECM connector that is fixed by disconnecting and cleaning. It's also possible you aren't getting codes because the battery gets disconnected.

Stalling at idle could totally be a stuck EGR or a vacuum leak. A vacuum leak has its worst symptoms at idle.

 

[chappys4life]

First off, you need to find out what is causing that check engine light to flash.
When a check engine light is “on” that means the ECM saw a problem and has a stored code.
When the Check engine light is flashing, the ECM is seeing a problem currently.
Light flashing = problem currently exists.
You need to know what that problem is. Secondly, Stop throwing parts at it, hoping to get it.
Spend the money on a code scanner that can give you OBD2 information.
TBI systems are super basic, and not hard to comprehend. You just need a little information.

This is not a ob2 car. Its a paper clip and flashing lights you count. There are none. I wish it was OBD2

 

[6872xtc]

One thing that I would be suspicious of is the ignition module in the distributor, as I put a complete distributor in a '95 truck with TBI. It was a Spectra Premium. It started cutting out, but not dying within 15 minutes of the first drive. Since I knew of several people having the same experience with the replacement distributors, some very soon, some after some time.
I installed the module out of the old distributor, since it had worn out bushings on the shaft.
That cured it, however I had to put a new Delco module in about a year later. I guessed that I hadn't used enough of the heat sink paste when I moved it over.

Not that this is sure fix, just what I ran into, as well as a know problem with complete replacement distributors a few years ago.

You can pull and plug the vacuum line going to the EGR valve and see if there's any change.

 

[chappys4life]

I don't know if these guys are still in business, but having data goes a long way for troubleshooting: http://aldlcable.com/aldl.asp.

A lot of good suggestions have been given, but this one still seems to be a mystery:

I have heard of a few cases where something goes bad with the ECM connector that is fixed by disconnecting and cleaning. It's also possible you aren't getting codes because the battery gets disconnected.

Stalling at idle could totally be a stuck EGR or a vacuum leak. A vacuum leak has its worst symptoms at idle.

I am really wondering if its the ecm. It would make the most sense with all of the parts replaced around it. I understand checking the fuel pressure but the pump is 1.5 years old tops and delphi

 

[6872xtc]

I am really wondering if its the ecm. It would make the most sense with all of the parts replaced around it. I understand checking the fuel pressure but the pump is 1.5 years old tops and delphi

My limited experience is that those old ECMs are pretty durable.
I may still have a spare or 2.

My one experience with a failing fuel pump had poor performance when accelerating, then refused to fire up after I shut the engine off.
I have witnessed a new Delphi pump being weak in an '02 8.1 truck, but it tripped a lean code when towing. Not that yours is showing a code, but Delphi isn't failure proof, even though they used to be close.

 

[chappys4life]

My limited experience is that those old ECMs are pretty durable.
I may still have a spare or 2.

My one experience with a failing fuel pump had poor performance when accelerating, then refused to fire up after I shut the engine off.
I have witnessed a new Delphi pump being weak in an '02 8.1 truck, but it tripped a lean code when towing. Not that yours is showing a code, but Delphi isn't failure proof, even though they used to be close.

Thats the thing when im on the highway it runs great. Why im doubting the fuel pump. I do see how the regulator could be an issue

I am actually taking it tomorrow to get the ac redone with new condenser, compressor, drier. Going to pickup a fuel pressure regulator kit PR131 and coolant sensor to see if they will do that as well. Hoping its that simple.

 

[Wes Harden]

Coming to a stop from cruise 40mph and above,then stalling is a symptom of an egr leaking( vacuum leak into intake). The Egr solenoid may not be venting properly. The solenoid has a foam rubber filter over vent port,normally under a plastic cap.
The Egr valve itself may be carboned up and not seating.
Next time it stalls and wont restart give the EGR a mild rap on top, don't bend it,then try and start. If starts the EGR wasn't closed.

The ecm coolant sensor need could be in error. There are to ecm grounds on the t stat housing,tgey get left off and abused. Check that they are good.

Beem my experience the TBI likes 12-14 psi. Do check the injector spray pattern,should be a nice cone shaped curtain,no spilts or drips.
The tbi base gaskets are kinda weak and will split creating a vacuum leak.

Not a fan of aftermarket ICM (ignition control module),but also hard to trust AC Delco stuff these days.

 

[Blue85]

This is not a ob2 car. Its a paper clip and flashing lights you count. There are none. I wish it was OBD2

Yes, you can scan codes and data with OBDI. Look at the link I posted above. Granted, it's more limited than OBDII and the implementation is more specific to the vehicle. Why would they have a 12 or 16-pin connection if the intended interface was a paper clip?

You can check out https://shop.moates.net/products/aldu1-and-cabl1 and https://www.gearhead-efi.com/. There were some other tools available like OTC3211, Actron 9690, MT2500, OTC4000E and Bosch OBD1300, which I have no experience with.

I am really wondering if its the ecm. It would make the most sense with all of the parts replaced around it. I understand checking the fuel pressure but the pump is 1.5 years old tops and delphi

The thing is, ECMs rarely go bad. They do sometimes develop bad connections.

 

[Blue85]

Delphi isn't failure proof, even though they used to be close.

This is a good point. Parts are getting worse all the time and many are "bad" or "not great" when you take them out of the box. This is why a nearly new ignition module can still be suspect. A lot of the Delphi aftermarket is just boxing from other manufacturers now, just like how AC Delco hasn't made a spark plug in years, but their boxes are in every store.

 

[chappys4life]

This is a good point. Parts are getting worse all the time and many are "bad" or "not great" when you take them out of the box. This is why a nearly new ignition module can still be suspect. A lot of the Delphi aftermarket is just boxing from other manufacturers now, just like how AC Delco hasn't made a spark plug in years, but their boxes are in every store.

Sure I get that. The think that makes me not think it is the fuel pump is on the highway or at steady rpm the light was flashing but not surging pops just smooth at 50mph. Why it makes no sense. I wish it would throw a code.

 

[chappys4life]

Coming to a stop from cruise 40mph and above,then stalling is a symptom of an egr leaking( vacuum leak into intake). The Egr solenoid may not be venting properly. The solenoid has a foam rubber filter over vent port,normally under a plastic cap.
The Egr valve itself may be carboned up and not seating.
Next time it stalls and wont restart give the EGR a mild rap on top, don't bend it,then try and start. If starts the EGR wasn't closed.

The ecm coolant sensor need could be in error. There are to ecm grounds on the t stat housing,tgey get left off and abused. Check that they are good.

Beem my experience the TBI likes 12-14 psi. Do check the injector spray pattern,should be a nice cone shaped curtain,no spilts or drips.
The tbi base gaskets are kinda weak and will split creating a vacuum leak.

Not a fan of aftermarket ICM (ignition control module),but also hard to trust AC Delco stuff these days.

I will try that. Is there any egr parts I should change or clean? The motor seems strong but I get at somewhere around 300k (odometer broke at 267k) things go wrong why I am open to change parts knowing they are 35 years old and lots of miles.

I think the tbi can be good but its one of those age and milage has taken a toll and troubleshooting/support is not ideal why I am looking at options. I was really considering a terminator x but after the 3600 price tag a carb looked better.

 

[warrpath4x4]

I have been having trouble with my TBI also but mine doesnt show any codes or lights. I have two OBD2 scanners that say they work on OBD1, but the connector is the wrong size. I was looking for an adapter cable and found many but most have reviews that they dont work because theres no pin powering the scanner. I found this guy today and ordered the parts to make a USB wiring adapter. Just have to ask the wife if I can use her laptop as I only have a work supplied one lol.

 

[doubletrouble]

I have an adapter kit that I got from Snap On, you can either plug into the cigarette lighter or the battery. I have two scanners that I can read codes on and data log and see live data on my OBD1 TBI.

 

[chappys4life]

Thanks. Made a bid on a mt2500 on eBay we will see what happens.

Today I started it to take it to the mechanic and the idle seems high. Hoping this will help find a problem