Running rich/rough
Thread Starter
2nd Gear
Joined: Apr 2017
Posts: 2
Likes: 0
Running rich/rough
Hey everyone,
Just bought an 85 corvette and the brake booster immediately went out. I replaced that and the battery and now it starts but struggles to idle and stalls. The hissing from the booster is no longer there but I figure I must have screwed up a vacuum line in the process. Any tips would be much appreciated cause I haven't found anything obvious.
Thanks!
Just bought an 85 corvette and the brake booster immediately went out. I replaced that and the battery and now it starts but struggles to idle and stalls. The hissing from the booster is no longer there but I figure I must have screwed up a vacuum line in the process. Any tips would be much appreciated cause I haven't found anything obvious.
Thanks!
Team Owner
Joined: Jul 2004
Posts: 28,379
Likes: 3,262
From: Hartford WI
Start with this. Fuel pressure: What is it when you turn the key to run but not crank? Will it hold pressure? What is it with a WOT run?
Spark, when running, is it a blue flame? Put an inductive timing light on each wire and see if it is steady. I did it with one that tells RPM and look for a reasonably constant value. When it is dark and you run the engine, spray a fine mist of water around the plugs and see if it has a light show. IF so, the wires are shot.
If that is all ok, now you have to pull each individual hose off the manifold and plug it with your finger and see if anything changes. IF it does, that hose has a leak somewehre.
Last thing for now is to clean the TB. Take it off. Take top plate and IAC off, take housing off. Clean everything but the IAC with brake cleaner. After which, you spray a gentle stream on the pintle and wipe gently. DO NOT PUSH OR PULL. Reassemble with fresh gaskets.
Spark, when running, is it a blue flame? Put an inductive timing light on each wire and see if it is steady. I did it with one that tells RPM and look for a reasonably constant value. When it is dark and you run the engine, spray a fine mist of water around the plugs and see if it has a light show. IF so, the wires are shot.
If that is all ok, now you have to pull each individual hose off the manifold and plug it with your finger and see if anything changes. IF it does, that hose has a leak somewehre.
Last thing for now is to clean the TB. Take it off. Take top plate and IAC off, take housing off. Clean everything but the IAC with brake cleaner. After which, you spray a gentle stream on the pintle and wipe gently. DO NOT PUSH OR PULL. Reassemble with fresh gaskets.
Thread Starter
2nd Gear
Joined: Apr 2017
Posts: 2
Likes: 0
The engine is new, 4000 miles on it, and it was running like a charm before the booster replacement. This is why I am thinking vacuum. I have already plugged the hose going to the booster where it comes out of the intake, but will do further vacuum tests. I currently do not have access to pressure gauges.
When removing the battery, I moved the cruise control servo out of the way and am not sure whether this would affect anything. I will try the spark test you mentioned tonight.
When removing the battery, I moved the cruise control servo out of the way and am not sure whether this would affect anything. I will try the spark test you mentioned tonight.
