Express 3500 nightmare - 5.7L Runs Rough

[Deennoek]

Hello, I have been reading up a lot about the common problems with these Chevy Express vans that run the spider fuel injection systems.
I recently bought a used Chevy Express 3500 with the 5.7L motor for work purposes. Right after buying it, I gave the van a complete tune-up and replaced several suspension items. It ran great for about 20,000 miles, but now the chevy express 3500 engine is not running well at all.
The check engine light flashes specifically at idle. So far, I have replaced all the related sensors, swapped out the fuel spider injector assembly twice, and even replaced the entire distributor assembly. I also checked the compression, and all cylinders are reading consistently between 115 and 120 psi.
Everything I try ends in the exact same result: a flashing check engine light at idle. If anyone has run into this specific issue or has any ideas on what I'm missing, please post on this subject.

Thanks for reading!

 

[SpareParts]

Hook a scanner to it and find out the problem. If you have a check engine light you should have a code telling you what to look at.

 

[Tonyrodz]

Have you checked your cats to see if they're clogged?

 

[strutaeng]

Try to determine which cylinder(s) are misfiing via advanced scan tool.

Compression is a bit low, not sure if that will cause a misfire?

Usually your classic issues on that engine running with misfire are:
1. Distributor (they wear and aftermarket replacements are usually junk out of the box).
2. Spider injectors (do a injector balance test even though they were replaced)
3. Ignition control module (ICM)
4. Intake manifold gaskets if they start leaking internally.
5. Other issues as other engines, like spark plug, vacuum leak, etc.
6. Fuel delivery issues

Pull your plugs for inspection. If you are losing coolant, you can pressurize the coolant and see which cylinder spits out coolant with spark plugs removed and spinning over a few cranks. Those engines are notorious for intake manifold leaks. Even the supposedly improved aftermarket Felpro gaskets fail in short time, and leaks are hard to pinpoint.

 

[SpareParts]

Spider injectors are a problematic. Did you put in the new MPFI style injectors?
Low oil pressure will also make the light come on and off at idle.

 

[Tonyrodz]

I still recommend checking the cats to see if they're clogged. If he's having injector issues, they've most likely were dumping excessive fuel which could clogged the cats, causing a flashing cel. One of mine were clogged, but there was no real loss of power. My cel would also flash rapidly.