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350 TBI Running extremely rough, can't solve

G

GrizzlyFabworks

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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
1-151
8-124
4-148
3-146
6-145
5-146
7-141
2-152

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!

Thanks,
Jeff Brewster
GrizzlyFabworks
 
You have to divide and conquer here. Stop trying to guess what part is bad and start trying to learn what's going on. Sometimes new parts are bad. I'm thinking mostly of the EGR and the ignition module.

The low pressure in #8 is a little concerning, but may not be the problem. Can you do a leak down test?

You can check for vacuum leaks with carb cleaner or propane, except for a stuck EGR, so you might pull that to test.

Try eliminating 1 plug wire at a time to isolate the problem to a cylinder. If that finds one, swap plugs and wires around to see if it moves. I've seen a simple porcelain crack in a plug make it run like you describe.
 
Yes egr can be stuck, while it's running poorly remove vac line and smack the top with screwdriver handle. If it starts running better it was stuck open.
 
Not sure if you have an ALDL port on an 87, but if you do that would probably give you some insight. At least it would tell you if you're misfiring or your timing is off.
I know it's been said before, but new parts are often bad right out of the box...you may want to swap that ignition module with the old one and see if it helps...Good luck!
 
anwat said:
Not sure if you have an ALDL port on an 87, but if you do that would probably give you some insight. At least it would tell you if you're misfiring or your timing is off.
I know it's been said before, but new parts are often bad right out of the box...you may want to swap that ignition module with the old one and see if it helps...Good luck!
Click to expand...
I have an obd1 port if that’s the same thing? I have a little “quick scanner” that jumps the pins but it doesn’t flash any codes. Is there a way to actually scan and obd1 system?
 
yes there are obd1 scanners. some will do both I and II. You should get a code 12 flashing on the MIL with engine off. Does the MIL light with the key on engine off ?
 
So it sounds like the idle is too low? If everything checks out (no vaccum leaks, egr is operating properly ect). You can turn the idle up on the throttle body.
 
Yes, TBI really isn't designed to have idle monkeyed with. It generally won't fix anything, and will usually cause other problems. The ECM knows what idle RPM is supposed to be, and will always use the IAC to try and maintain that.

"Setting minimum air" is a procedure to make sure idle is proper, but is only really needed (sometimes) when components have been changed.
 
dyeager535 said:
Yes, TBI really isn't designed to have idle monkeyed with. It generally won't fix anything, and will usually cause other problems. The ECM knows what idle RPM is supposed to be, and will always use the IAC to try and maintain that.

"Setting minimum air" is a procedure to make sure idle is proper, but is only really needed (sometimes) when components have been changed.
Click to expand...
Is that the technical term for making sure the IAC valve is in the right position when you install a new one? I remember having to go through a list of steps to get mine correct, I'm sure they are listed somewhere on the site. I agree, though, that you need to identify why the idle is off...the ECM is getting some bad info from somewhere...it didn't just go bad for no reason. Is it a steady low idle, or does it surge?
 
I don't know as that is the technical term, but if you Google it, you'll get the proper procedure per GM.
 
is this throwing any codes? all ya needs a paper clip.... anything remotely finnicky in the EGR system will usually throw a code.. ignition side too...

what are the plugs showing? are they even among cylinders? bring it up to like 1800 and pull plug wires with grounded pliers....
 
I was also going to suggest checking the codes with the paper clip. Sounds like it might be running in limp mode.
 
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