TBI 350 woes

rockcity

rockcity

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Joined
Apr 10, 2005
Location
Greenville, NC
1990 tbi 350 runs ok for a sort time then runs rough then dies. It won’t start back (even with ether) for another hour or so and the cycle repeats itself.

CEL came on but father in law doesn’t have a scanner to check and I’m 2 hrs away.


Anyone have experience with these engines to maybe at least point in the general thought as to where to start (other than the obvious of checking the CEL codes)?


It almost sounds like vapor lock to me. FIL explained that he felt like it was getting too much fuel and couldn’t burn it all and was running rough, etc. that may be O2 sensor related or something with that air/fuel ratio but I don’t know these motors enough to have an idea what sensors could start to cause that condition.
 
I was also thinking loss of spark. It where I would start. Pull a plug and see if it hits with any spunk.
Should also be petty easy to see if the old school squirters are working if this is the tbi I have in my head. Or at least see if it's got fuel up on the rail to it.

Do these use a coil and module? My tech isnt real savy on specifics. But any of my rough sniffing around involves these first.

If all that seems good....do these rely on a CPS for firing signal?
 
I was thinking CPS as well but I wouldn’t think it would run then not after a little bit. Dunno.

It’s a 1990 motor in a suburban.


I’ll see my FIL next weekend and was trying to get some ideas before I get there and plug the scanner in to check the codes.
 
'90 TBI is throttle body. There's a module below, not in, the dist cap that could be going/gone bad. But check the rotor button and cap first, then to see if you have spark on plugs. They need 9-13 fuel PSI but really close to 13 to run correctly. You can watch the fuel spray from the injectors in the throttle body and see if it's breaking down. Maybe pump is going bad. lean can act like too rich too. How long has fuel filter been on it? Check grounds to pump.
I'm sure Youtube has instruction on how to test the module, because I don't know. good luck with it.
 
I would check fuel pressure. It might be one of those without an accessible port to connect gauge. I soldered an access port into a fuel filter to check my tbi.
 
Cps, the heat is screwing the hall effect. When it cools. Works fine.
 
Check for spark and look for injectors spraying after it dies. If so ignition module and pickup are good.

Coolant sensors are a known issue on these as well. If it's reading off it will run badly, Flood or lean.

Check spark and fuel first, then you need to jump the aldl connector and get codes to dig deeper.

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Unplug coolant sensor and see if it'll run!! Had same issue with my tbi.
 
I’ve got Noid lights and a OBD1 code checker if you need it. These don’t have a crank trigger so it’s not going to be a crank position sensor, it’s all done through the distributor/ignition control module. The coil pickups are bad about going out, I just diagnosed this on my k5. If you’ve got injector pulse and some spark then it rules out your ignition control module.
 
I’d be suspecting the ignition module. I have the TBI system in my Jeep, and in my experience they run shitty in limp mode (with a defective sensor) but the ignition module is a show-stopper . The modules need good thermal contact to the distributor housing, if not, they overheat and fail.
Hope that helps
 
If there's trouble codes stored, you don't need an OBD1 scan tool... just a paper clip.

Find the ALDL under the dash, connect terminal A and B together with the paper clip. The check engine light will flash the "12" code three times, then will flash any stored codes. The "12"will show as one flash, pause, two flashes, pause, then repeat.

ALDL pinout shown here.
IMG_1948.GIF


Write down whatever codes it flashes then look them up. That's the only leg work needed without the scan tool.
 
Scooter402 said:
If there's trouble codes stored, you don't need an OBD1 scan tool... just a paper clip.

Find the ALDL under the dash, connect terminal A and B together with the paper clip. The check engine light will flash the "12" code three times, then will flash any stored codes. The "12"will show as one flash, pause, two flashes, pause, then repeat.

ALDL pinout shown here.
View attachment 267830

Write down whatever codes it flashes then look them up. That's the only leg work needed without the scan tool.
Click to expand...

Used to do this on my 4.3 in my willys. Great advice. I had forgotten all about this.
 
Jeff B said:
Used to do this on my 4.3 in my willys. Great advice. I had forgotten all about this.
Click to expand...
I always joked about my diagnostic tool being a paper clip when I had TPI in my CJ many moons ago. :D

EDIT: I forgot to say in my original post -- once you ground the diagnostic terminal (A to B), turn the key on. It doesn't work only on mind bullets. :lol:
 
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A little late seeing this. If I had seen this when you posted it I could have let you know immediately. I have a TPI set up in my YJ and I had the same issue about a year ago. The mine ended up being the pig tail and not the CTS itself, but caused the same problem.
 
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