Does anyone have a thoughts on why my 1994 would run rough after warm-up? I had it
In the shop, the fuel pump replaced, and EGR valve replaced. The check engine is NOT giving a warning. However, it will not pass the emissions and the fuel mileage is terrible! Help.

 

Terrible fuel mileage and not passing emissions gives me the suspicion that your spider/nut kit/CPI is leaking. You may have read on here that the fuel injection system on these trucks is prone to leakage. I would get a fuel gauge and test the fuel system. Put the gauge on the fuel pressure test port on the left side of the engine behind the intake manifold. It's near the distributor. Turn the key on but do not start the engine. The fuel pump should come on. It should pump up to between 55 and 60 psi. Then start the engine. Fuel pressure should remain steady. Let the engine run a few minutes. Fuel pressure should still remain steady. Shut the engine off. Fuel pressure should not drop more than a couple psi for five minutes. If at any time the fuel pressure drops then you'll know there's a leak somewhere in the system.

 

i second that!

 

also has anyone checked to make sure the catalytic conv is`nt clogged?? how high are the emissions readings that it`s failing?

 

Dont go to that shop again... Strapping on the pressure gauge takes a whole 5 seconds - every technician owns one - and its part of the diagnosis process... Also chances are your EGR was still fine and only needed to be cleaned out - waste of 200 bucks for that part. A failing spider assembly is something that any techinician would know to look for on the older CPI engines if he knew much at all. Save yourself some money, dont pay the shops... Order yourself a test gauge online and check this problem out yourself.

Or do it the easy way, pull your motor oil dipstick, its going to be overfull and smell like gas - you have a leaky injector.

If you are high on HC emissions, a trick alot of poeple like to use is run the tank down to 1/4 or less, and pour a gallon or two of METHYLHYDRATE into the tank - now go for testing you will ace it. This stuff is alcohol, not hydrocarbon fuel so it cant make a high HC emission rating. Just when you get out of the test station to fill the tank with gas to dilute it cause it will dry out rubber gaskets and such. It will clean out your fuel system nicely too, and your engine will make gobs more power on alcohol too.