Un-fixable Rough Idle 94 Fs Blazer

BigBlaze · February 26, 2010

I am officially at whits end.. My 94 full size blazer has a intermitent rough idle (feels like a dead misfire). The truck has never shut off during one of its episodes... Has never set the SES for this problem(yes the SES light is functioning correctly)... Seems worse on a cold start and once engine is at running temp. Just replaced the engine, but had the same problems with the old engine.

List of new parts over the past year: No i'm not a habitual parts changer. most parts got replaced with new engine!

plugs, wires, cap, rotor, reman distributor, ignition module(module died three days after replacing dizzy), coolant temp sensor, o2 sensor, IAC, knock sensor, etc...

TBI unit has been rebuilt, checked for vacuum leaks, fuel pump checks out, pressure and volume, all sensors in spec..

Any ideas?? RUNNING OUT OF HAIR TO PULL OUT!! use to look like this guy------> now this----->

Nytemare · February 26, 2010

I am officially at whits end.. My 94 full size blazer has a intermitent rough idle (feels like a dead misfire). The truck has never shut off during one of its episodes... Has never set the SES for this problem(yes the SES light is functioning correctly)... Seems worse on a cold start and once engine is at running temp. Just replaced the engine, but had the same problems with the old engine.

List of new parts over the past year: No i'm not a habitual parts changer. most parts got replaced with new engine!

plugs, wires, cap, rotor, reman distributor, ignition module(module died three days after replacing dizzy), coolant temp sensor, o2 sensor, IAC, knock sensor, etc...

TBI unit has been rebuilt, checked for vacuum leaks, fuel pump checks out, pressure and volume, all sensors in spec..

Any ideas?? RUNNING OUT OF HAIR TO PULL OUT!! use to look like this guy------> now this----->

Sounds like you have a ground fault in the engine harness...or body harness or a bag ignition relay. My guess would be to replace the relay that controls your ignition...IGN1 comes to mind...but you need a manual to be sure. Sometimes the relays get worn out and start to fluctuate (the magnetic coil part...not the switches). There should be a butt load of relays in the relay box that have the same part number as your IGN1 relay, you can just swap them. Or they're 12 bucks for a new one....This could be the case with the fuel pump relay too...causing the fuel pump to intermittently shut off and come back on.

BigBlaze · February 26, 2010

I'm fimiliar with the dying relay, had a trans am pull that one on me once.

I can't find any ignition relay on the truck, or on alldata... maybe time to check harness wires though.

BigBlaze · February 27, 2010

any more suggestions. i plan on attacking my truck again first thing in the morning... hopefully with a brain full of fresh ideas.

Nytemare · February 27, 2010

any more suggestions. i plan on attacking my truck again first thing in the morning... hopefully with a brain full of fresh ideas.

I cant remember...but doesn't that year truck have a fuse-able link? Usually they cause problems when the heat shields fall off the stock manifolds or when a set of headers are installed. It should be on the firewall on the passenger side, if it has one.

BigBlaze · February 28, 2010

yesterday i decided to go over the ignition with a fine tooth comb, and upon pulling of the dizzy cap... a hold down bolt broke off in the dizzy... had to pull the dizzy to remove the bolt...... guess what....the reluctor wheel was rubbing. replaced the dizzy and it now runs great!!! so much for the reman i put in a year ago.

Thanx to all who offered a helping opinion!

BigBlaze · February 28, 2010

or should i say. Thanx Nytemare!!!

redvett · February 28, 2010

Do a compression test.

Nytemare · February 28, 2010

Do a compression test.

Good idea....I've seen bad things happen due to similar dizzy problems. Rebuilt an engine a while back where a guy got water on the cap and corroded the terminal for #5 cylinder. when I popped the head off and removed the valve, I could remove the valve seat with my fingers and the head was cracked between the two valves. All due to a rough idle. Compression test will tell you a tonne of info.