I have been trying to pull codes from my 1991 F-150 302 v8 but after hooking up the jumper wire it does nothing.No flashing light , nothing at all, but the check engine light does work , as I have seen it before My understanding after hooking up the jumper wire to the top right port and to the grey separate port, you should get a verification flashes, but I am not getting those at all So why am I not,I got the firing order straightened out, it runs but has a slight miss but has 130 lbs of compression on the lowest of the 8 cylinders,and 165 at the best compression of the 8 cylinders. I've replaced coil, engine temp sensor, distributor control module, I jectors,fuel line pressure regulator, fuel filter,throttle position sensor,col start valve,, and am about to put new muffler on it as this truck say for 14 yrs,and now is getting rebuilt bumper to bumper.But still I have a miss when you go to drive it,a hesitation which drives me crazy! Does anyone have any ideas what I am missing or what could be the problem? This forum has been a HUGE help and am very grateful for your help and input! Thank You Dave H.


It finally gave a code 33, which looks like egr opening not detected, I checked compression and it is 120 to 130 lbs on all 8 cylinders, but it still has a weird miss, I did compression test and found #2 and#4 plugs were black with carbon, but the rest looked ok but old for their short time in the engine I cannot figure out what is causing the miss.Have changed coil, plugs, injectors, fuel pressure regulator,cold start valve, throttle position sensor, temp sensor at thermostat,pcv,waiting on EGR valve, plug wire seem fine as I misted them with a water bottle at dark and saw no sparks or cross firing, new distributor control module.I was told that my floppy muffler could cause the missing in the engine as it is sending nothing thru the rear tail pipe! Any help will be greatly appreciated Thanks again Dave H


I replaced the EGR Valve and erased codes, took negative cable off, as I was told to do, and after trying to get codes over 20 times, it gave me codes 2 times, the check engine light comes on when ignition is turned on, but it doesn't give codes or the confirmation code like it is suppose to and it is idling ok but sometimes it acts like the ignition is being turned off instantly and turned back on before completely dieing, as if electric is being cut off for a split second, could my computer be bad? It costs more than I want to take a gamble with, if it's bad,I will replace it, but if not, why waste the money! Any thoughts on this will be appreciated.Thanks again!Dave H.

 

If you did the jumper and it’s not going into test mode. You need to pull the computer. It’s probably got some leaking capacitors and damaged the board.

 

You could try running a ground straight to the battery negative from the single wire self test initiator connector, instead of using the ground at the diagnostic plug.

 

Where is it, my Chilton's does say it is under dash, but that is all, so where is it, as I figured it was bad,as I could only get codes randomly, sometimes I got a code but mostly did not get codes Thanks Dave H

 

It’s behind the driver side kick panel. Remove the panel and you’ll see it. Remove the harness connector from engine bay side, then remove hold down clamp and pull computer from inside.

 

Had to loosen fender bottom and inner splash apron to get ECM plug to have enough room to come off, but it finally did, found a replacement at local parts store, it will be here in 5 days, but got new Flowmaster super 44 muffler installed, along with every sensor it needed,as it sat for 16 years. and after each replacement it would run a bit better, and better the more parts I replaced, but it was still not quite right, so when it would not give up it's codes using the jumper wire method I chose to buy a new eec/ computer it better run smooth finally!! Thanks for all the help, will keep you up to date on the rebuild as I'm rebuilding it bumper to bumper.Have repair panels and 8 ft bed sides, as I had a body shop for over 45 years. Thanks again.