Check Engine light

[genegr]

On my 91 GT 5.0 the CEL comes on during acceleration then off when I let up to shift. It will not come on if your just sitting and rev up the engine so it's bin hard to test with the code reader. I replaced the four vaccum lines at the rear of the passenger side engine compartment. Spark plugs look a little white. thanks for any ideas. 118,000 miles to date

[mustangmike351c]

my be going lean under acceleration. check fuel filter

[SkylineUSA]

What gas are you using? 87,90,91,93?

[genegr]

Been using 87 octane, I have a full tank and it takes me a month to use that, should I try an octane booster? Looking at the fuel filter it looks to be original, I will get that changed ASAP. thanks

[SkylineUSA]

It akes a full month to use a tank, go open her up on a good run, and see iuf the does anything

Just a shot in the dark, run some 93 when you get a chance, see if things change then as well.

[KimMG]

Check to see if there are any stored codes. It is best to find out why the light is coming on instead of guessing.

[genegr]

thanks, tried the STP octane booster and new fuel filter, no change. I'm trying to find someone in the twin cities with a drive on dyno. The local shop didn't find any stored codes but he thought the dealers may have a better code reader then his.

[dorfboy]

Before all that, try the upgrade in octane and change out your CO2 sensors. You may be getting a slow response from either one or both. Since it takes a month for you to blow through a tank of gas, you might have some junk in your tank.

[genegr]

It was 39 deg outside temp yesterday when I took it for a ride. The light didn't come on till the engine was about 165 deg, then would come on during acceleration. The light would stay on above 75 mph even when I lifted till I was below 75. I ran the tank down to 1/4 full then filled with 92 octane with no change on the ride home. I didn't mention earlier that the low fluid light is on all the time, could this be the germlin that I'm chasing? thanks

[mustangmike351c]

Originally Posted by genegr

It was 39 deg outside temp yesterday when I took it for a ride. The light didn't come on till the engine was about 165 deg, then would come on during acceleration. The light would stay on above 75 mph even when I lifted till I was below 75. I ran the tank down to 1/4 full then filled with 92 octane with no change on the ride home. I didn't mention earlier that the low fluid light is on all the time, could this be the germlin that I'm chasing? thanks

do you have any exhaust or vacuum leaks? if you can put a scanner on it I bet the light comes on because of an O2 senor is reading lean. you should have codes stored any time the cel comes on.

[reekor]

I would clean the MAF sensor, and even more so if you have a oil charged air filter in the car (K&N).

After reading all of this, I just can't help but think that it's EGR related. I would remove the EGR valve and make sure the that EGR channel is clean and that the EGR valve is working. Then I would check the EGR vacuum regulator and clean the foam filter in it. If that all turnes out to be fine I would replace the EGR Valve Position (EVP) Sensor.

[KimMG]

Low fluid light? Problems can compound. What fluid is/was low and have you corrected this? What are the codes you are getting from the CEL? White spark plugs are indicative of running lean. Is the O2 sensor working properly?

[genegr]

Stopped in at the local Checker Auto Parts and they had the OBD1 tester availible, three memory codes came up. #14 Profile ignition pickup circuit failure. #31 EGR valve position or exhaust pressure transducer sensor voltage low. #96 Fuel pump circuit failure or high speed fuel pump relay circuit failure. All the info for each kinda leads to replacing the fuel pump and EGR valve.