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TBI 350 runs extremely rough, can't solve


Premium Member
Jun 15, 2021
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Northglenn, CO
Hey guys!

This is my first post here as i've never been a paid member up until recently, but i've always used ck5 threads since i've owned my k5. However i'm now in a spot where I can't figure out my problem here whatsoever. This will be a very long post but please bare with me here.

1987 K5 Blazer, 350TBI/700r4/208, I recently installed the ORD Fush kit that i've had sitting on the shelf for awhile, truck ran really great and drove smooth on it's first drive back, but I did make 1 stop, and when I go to leave the truck has a random misfire out of nowhere. I had the hassle of passing emission 6 months prior so the cap, rotor, plugs and plug wires and O2 sensor are already "new" with very very little miles on them as I rarely drive the truck as is. I've done tons of research and dug through all the online threads I could get my hands on I started with some trouble shooting.

Vacuum test at the intake manifold port showed a very low reading, making me believe the timing needed adjusted
After some research I let the truck warm up to temp, shut the truck off, unplug the ECM wire, and restart the truck
Using the timing light I re adjust the timing to the factory 0 degrees to no avail.

Compression test just to cover my bases had the readings as follows

Fuel Pressure test showed about 12-13psi at the inline fuel filter along the frame rail of the truck

The majority of the parts I started to replace I have purchased prior and just warranty swapped the parts out for piece of mind while trying to chase the problem down.

New Distributor assembly even though I just replaced the cap and rotor not long ago
I made sure to reset the timing with the ECM wire unplugged, and have done so multiple times now
New timing chain set, the old set had skipped a tooth and the chain was extremely loose
New timing chain cover and front oil seal
New Oil pan gasket with the timing chain install
New Egr valve
New Egr solenoid
New Map sensor
New Electronic spark control module
New Idle Air Control Valve
New Throttle Position sensor
New Coolant temp sensor

With all the new parts installed along the way, the truck has made an improvement, but it idles great on start up, but when you drop it into gear it still runs rough, gutless almost and struggles to keep a steady idle at stop lights once the truck is warmed up. I'd really appreciate any insight on what my problem is here!

Jeff Brewster

Wes Harden

3/4 ton status
Premium Member
May 28, 2005
Reaction score
Lake Havasu City AZ
Start investigating the TBI. engine off open throttle look down the barrel for base gasket sticking out. Inspect wire to injectors. If good start engine air cleaner off, watch spray from injectors. You want a nice even cone spray. No gaps in cone, no drips.
If all that checks out remove the IAC clean the pintle, light machine oil on threads, pipe cleaner in passage with carb spray.
Inspect the vacuum line to the MAP sensor.

Good luck let us know what you find


Puppy Fabricator
Premium Member
GMOTM Winner
Jun 13, 2003
Reaction score
Jersey Shore
you can spy your spray pattern a bit better if you watch it to a timing light strobe in low light.....
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