1990 Suburban engine issue

[b79holmes]

Hi all,
This morning, I went to start my ’90 suburban (TBI 350), and it was doing something very odd. It nearly started on the first try, but immediately died. The ‘Service Engine Soon light came on. The next two tries, it didn’t fire at all. It usually starts easily. I tried again with my foot on the floor, and it started. It ran really rough for the first 3 or 4 seconds, but then it smoothed out. I held it at about half throttle for maybe 7 seconds, then let it go down to idle. It seemed to be idling fine. It ran fine for ten minutes, but then I had to leave, so I shut it off. I quickly plugged in my ECM code reader, but it only gave me code 12, which means that the system is working. It gave no error codes.

I went back this afternoon and unplugged the battery for half an hour. It did the exact same thing when I tried to start it, only it blew a little more blue smoke than last time, but the smoke went away once the engine smoothed out. Once it was idling, I let it sit for about fifteen minutes. I wanted to see if anything changed when it got up to temperature, but when I came back, the truck was running at about 2100 RPM and the ‘Service Engine Soon’ light was off. I tapped the gas, and it smoothly gained revs for about a half second, then it spluttered down. I killed the ignition once I saw it dip below 500 RPM because it was clear the engine was going to shut off anyway.

Now, when I plug in the code reader, it doesn’t show any codes at all, not even code 12, and I’m not sure where to even start looking for problems. Anyone have any ideas?

The truck is a 1990 V1500 Suburban with 265,000 miles on it. It’s a Silverado with cruise control, and is completely stock.

Thanks,
Bill

[Ski-me]

Fuel Injectors, Fuel pump, Fuel Filter??? Guessing.....

[Irish1941]

Having read the post a few times, I'm leaning towards idle air control valve aka the IAC or the temp control switch on front of the block. Maybe both.
All seems to be idle problem.
Check the IAC to make sure it's working right.
If temp control is bad, it will tell ECM to dump fuel in like it's -40. High revs and raw fuel smell are give aways on that one.
If IAC checks out correctly, then go with fuel PSI and work out from there. As ski-me said, fuel pump and/or filter can cause major problems esp on a truck with that many miles. Most of the GM sensors age out around 100-140K so be glad it ran that long.

Loss of ECM connection and no codes is not a good thing & baffles me.
Codes then no codes...bad ground from ECM to chassis?

Best way to diagnose TBI is a PC, cable and WinALDL software.
Its a free download.
Do some reading here. This will go long way in helping you figure out your problem.
http://tbichips.com
TBI is a very simple EFI to work on once you understand how it works.
It only went from 87 to 95 in trucks & not much changed.