Chevy Blazer misfire help

astafford

95 blazer new pump plugs wires compression all within spec as well as fuel pressure replaced spider injection it was leaking like a mother in the intake. Tps and egr replaced as well. The problem has stayed the same after all this with the problem being multi missfire at idle and on first start up loped idle and driving down the road is impossiable. It never dies drinks gas but when you get about a quarter mile down the road it runs 90% better but not as much power as I believe it should. The check engine was around the egr. Weird thing is unless you drive it the check engine stays off once you finally make it down the road it just takes off like a bat outta hell and the check engine comes on. Any ideas? Driving my mad.

imidazol97

Does this engine have a fuel pressure regulator that has a vacuum line going to it? Search for youtube videos on checking FPRs. Remove the vacuum line check for liquid gasoline in the line or a strong smell of gasoline. Then restart the engine and run the engine for a while the vacuum line is off. After a couple minutes you may get liquid gas coming out leaking through the diaphragm inside that the vacuum moves to switch from low pressure to higher pressure. Could explain the higher fuel consumption along with the loping at start.

thecardoc3

The fuel pressure regulator is part of the spider assembly inside the upper intake. If someone suspects a leak, you can remove the intake manifold runner control valve and see it. Then its just a matter of commanding the fuel pump on to check for a leak. The most common leak on these are the plastic hoses that connect the spider assembly to the fuel lines at the rear of the intake manifold.

astafford

I had replaced that with the plastic hoses in the back it was cracked and throwing fuel like crazy but after replacing it didnt change the mpg were still just as bad and still running like crap. Since the install the upper intake has been pulled back off after months of driving and no fuel smell no puddles nothing. Im having suspicious about the coolant temp sensor being bad but im not sure. As I said you start it let it idle for two years if you wanted to and the idle would just bounce all around once you drove it less than a mile down the road it clears up and runs really well but gas mileage is still god awful and it seems like its down on power more than it should be. Also seems as if its running extreamly rich do to the smell of exhaust. Im just not sure if the coolant temp would throw it off that far. And I know this year does not have a mass air just that little air temp one in the intake tube.

thecardoc3

This is why a scan tool and not just a code puller is so important. By getting to look at the data that the microprocessor is using to calculate the injector pulse and spark timing map it eliminates all of the guess work. From there once the inputs have been verified the tech can then concentrate on the feedback system, specifically the fuel trim data.

When performed as a complete routine by a seasoned tech this all looks really simple, but it actually takes lots of experiences just like this one to teach all of the possible variables that have to be considered and ruled in or ruled out.