Ok.. 95 Blazer, W block, 4 door, 4wd, new engine (less than 3k ago), problems like you wouldn't believe.

So... here's the latest "issue"

I've got a rough idle, barely any pickup (no power), and it surges through accelleration unless I REALLY get on it, then it rev's up nice, but still has no power, and I have to let off the gas to let it shift. I was worried about transmission problems.

But...

Mechanic told me that the EGR valve appears to be "too clean" allowing it to open and close too easily.

SO.. he suggested a new EGR valve. I bought one (not cheap) fought with getting the old one off, and installing a new one, with the upper intake still on. (what a pain in the A double snake) .

Started it up, and weeee hawww. this new engine finally had some guts. For about half a block

Soon as the engine warmed up, rough idle was back, and the rough accelleration was even worse.

So I called my friendly mechanic, and he suggested I try blocking it off.

Did so, and once again WEE HAWW... it ran great . More pickup then this new engine has ever had.

But, he and others suggested that I do NOT run the engine without the EGR valve.

So... I brought the new one back, had it replaced, installed this newest one (pulled the upper intake off this time... SOO much easier), bolted everything back up.

Took off great again, wee hawww.... halfway down the block. But again, as soon as the engine warmed up, the hesitation during accelleration was back, and the rough idle was back.

Here's what's buggin me. NO CODES. None at all. None before with the old EGR, and none now with either of the new EGR's. But the rough idle and hesitation and lack of power is pitiful.

I can't get out of a three legged dog's way.

So... as I'm sure now that the engine IS ok, and DOES have power, thanks to the blockoff test. I'm stumped.

Two new EGR's, both cause the same rough running problem.

Block it off, run's great.

No codes at all.

So... what's my problem? Try for ANOTHER new egr valve?

I've heard that there are two EGR fuses, haven't found those, or looked yet, but I need to.

Could it be the wiring to the EGR?? All the other wiring on this truck is pretty useless.

Could this be another vacuum problem, as all the other vacuum lines are pretty useless too.

Could my cat converter be clogged?

and wouldn't most of these problems throw up SOME sort of error code? Scan tool for this OBD2 says NO PROBLEMS!!! Yeah Right... I told the OBD it could kiss my a double snakes and it could drive the darn truck then.

Help please

Thanks
Chris

 

Sounds like you have narrowed it down to an EGR problem for sure. And from the sounds of it, you have a problem with control aspect of the EGR valve.

The EGR valve will not activate until the engine is warmed up. It sounds like your issue is that once the EGR valve opens, your performance goes to garbage.

One thing that just popped into my head... Is the other end of the EGR supply tube connected properly? I'm not sure where the EGR gets its flow from on the older CPI engines, but if it was pulling in fresh air instead of inert exhaust gasses, it could cause the condition you are experiencing.

Was this engine "new" or "new to you"?

 

if it works fine bypassed leave it alone. every truck ive ever owned i bypassed that thing. i hear though sometimes it will cause the check engine light to come on

 

On newer engines, running it blocked off can cause problems. It will increase cylinder temperatures which can burn exhaust valves left to run like this.

 

Although I've swapped many engines for "new to me" before, this one is actually new from a manufacturer.

Yes the diagnosis is correct, Runs great until warm, and then performance goes to crud.

Not sure where the intake or pickup for the EGR is, but I'll have to read up on the details in the Haynes manual I have, and see if I can figure out if it's getting fresh air somehow.

Is there any way that the wiring could be bad, causing the valve to stay open once the engine warms up, instead of staying closed more? How would I diagnose that wiring?

And.. now that I know the fuel pump is caputt... due to wiring, or bad pump, or bad fuse, is it possible that my EGR problem, was caused by, or affected by, the fuel pump?

And... as my cat converter is original to the truck... if it's crud, would that cause enough back pressure to force the egr valve open, and thereby cause the rough idle and rough accelleration when it warms up?

 

every place I've looked, the answer is to clean the EGR valve, or replace it, and clean the intake. But I've got a NEW egr, and a new block, so.....??? and then everybody shakes there head, not knowing what to do next. The manual is not much help, so I'm stumped. Block it off, runs fine, leave it open, and it runs cruddy once it warms up. Something has got to fix this. Is it possible that the wiring to the EGR is bad? What should the wiring be doing? and where does it go?

thanks
chris

 

I have the same problem as you, I have replaced the EGR but once the engine is warm the idle is very rough, at runs great at speed however and starts perfectly.

I have begun pulling the code for the secondary air injection and here is what I am thinking. The air pump is not injecting air into the catalytic converter, therefore the O2 sensor downstream of the cat is detecting a lower than expected O2 amount which causes it to correct by reducing fuel in the cylinders leading to a rough idle. Once you get going the volume of gas that flows through the engine is much higher, thus the O2 sensor does not pick up the slight decrease in O2 from the air pump not pumping and the engine runs as it should.

I can relate to the frustration to this problem as it has lingered for a while.