1992 GMC 1500 - EGR Activation At Low Speed FIXED

[lewisautorepair]

*****FIXED*****HEY GUYS, GOT A 92 GMC 1500 WITH A 5.7l IVE GOT AN ENGINE STUMBLE AT LOW SPEEDS TRACKED DOWN TO THE EGR VALVE OPENING TOO EARLY. THE SOLENOID IS GETTING THE GROUND FROM THE ECM I JUST THINK ITS SEEING SOMETHING TOO EARLY OR A SKEWED READING SOMEWHERE. I WAS WONDERING WHAT THE PERAMETERS ARE FOR THE SOLENOID TO OPEN. LIKE SPEED OR RPM OR THROTTLE POSITION. ANY HELP WILL HELP. !!!!FIXED!!!!

[liljoe]

I think I would look at the EGR valve and make sure it is the correct one, if it is aftermarket I have seen a bunch with the wrong orface washer or no orface washer installed. It will make a huge differance if it is too large.

[lewisautorepair]

CHECKED THE VALVE AND NUMBER AND IT HAS THE RIGHT VALVE ON IT AND IT DOESNT TAKE THE WASHERS. THE VALVE PORT RECESSES INTO THE MANIFOLD.

[Tim Martin]

I am not a GM basher but beings its a 92 model with that issue, I'd be thinkin about a replacement ECM for it. I have seen a similar thing on an early 90s model and the ECM was at fault. On this one, make sure the fuel pressure and spark advance are ok. Those fuel pressure regulators can be adjusted slightly and will make quite a difference on performance.

[lewisautorepair]

WELL I FIGURED IT OUT I GUESS, THE TIMING WAS OFF BY ABOUT 4 TO 5 DEGREES. RESET IT TO BASE PLUS 1 OR 2 AND IT COVERED UP THE PROBLEM VERY WELL. DONT KNOW IF IT WAS THE PROBLEM BUT IT FIXED HIS PROBLEM. THANKS!

[Tim Martin]

I bin trying to think this thing through an understand the relation between timing and egr command. Need to study this one some time. Hey in the world of electronics, anything can happen. Don't we no that by now. Thanks for the update though. It does sort of illustrate a point of checking basics.

[ricmorin]

My guess is that the retarded timing affected the base engine vacuum. Adding EGR to it put drivability over the edge. EGR is usually determined by load and throttle position. Low vacuum is interpreted by the ECM as load. Just a guess cuz I specialize at not specializing.

[liljoe]

Ric, your speculation is right on the money, I have had a bunch of thse trucks in the past that just wouldn't run at the specified timing setting but ran like a scalded dog with about 4-6 extra degrees added to it, I think that the timing marks might not be the most accurate on these trucks. Thanks for posting the fix.

[Jeff @ Able Auto]

May want to check the crank dampner for slip. That would cause the timing marks to be off. Wouldnt be the first one. Have a good weekend all

[Tim Martin]

My guess is that the retarded timing affected the base engine vacuum. Adding EGR to it put drivability over the edge. EGR is usually determined by load and throttle position. Low vacuum is interpreted by the ECM as load. Just a guess cuz I specialize at not specializing.

Thats pretty much what I concluded although i'd like to prove it at some point in the future. Hey, thanx for the info.

[steven kiser]

bumping up the timing may be compensation for a weak chain. just for giggles remove the distrubuter cap and rock the dampner back and forth checking how much slop there is before distributer rotor moves. I'd expect to see 10 to 20 degrees slop in the chain from the information i've gathered from the postings. if so replace it and if you look at the cover you may just see where the chain has just about worn through near the bottom because of the chain slop.