Hello all I have a 1989 f-150 with a 5.0 and it runs great and strong until the check engine light comes on and it will flash sometimes on and off and when the light comes on it feels like you just hooked up a trailer to it, it lags until the light goes off and when it flashes the truck will lose power with every flash, then when you let off the gas it shuts right off then it will start right back up but if the light is on it shuts back off, the kicker is i have unpluged my most of my sensors and the damn trucks runs great ecexpt because of the light being on it is running in base mode and it does not have all the power it should. I put a new motor in the truck but two or three weeks before I put the motor in this problem started so I know it is not the motor, I have replaced every sensor three and four times the codes are saying low voltage to the knock sensor but then checked it is fine, this is kicking my *** so I drive it with the light on and the sensors unpluged any help would be great and the parts came from carquest so I know that they are good , I believe the wire harness may be screwed but not sure, and with I changed the plugs they had like a clay looking substance on them? I was running autolite 25s now I stepped up the heat to 26 but the 25s only lasted three months before they failed? please any one else have this problem and know how to fix it, thank guys

 

A code for the knock sensor sounds reasonable. If timing is retarded it will feel gutless. It also sounds like an intermittent short that may appear from road vibration but not all the time. What happens if you drive with only the knock sensor unplugged?

 

it runs the same no matter if you run it with just the knock sensor unpluged or everything unpluged as long as the check engine is on because a sensor is unpluged it runs great just in base mode not as much power and the time it is in perfect time, I have been struggling with this for a while. Now I noticed that it first gave me the problem as soon as I filled up with this lovley ethanol gas we have to burn I only run 93 and nothing else I have tried 87 and 89, I even put cam 2 in it and still the same. this is killing me I want to super charge it but until I fix this problem I can not do nothing.

 

Does it stay running badly long enough to put a timing light on it and see what the timing is doing at that moment? If it goes to base timing, I would suspect a problem with the SPOUT circuit between the distributor and the computer. If it only retards a few degrees, I would think the knock sensor circuitry as a more likely culprit.

 

no it just shuts off does not run bad or any thing it just shuts down then start it up and it is good until the light flashes

 

Do you know where I can get a engine wire harness?

 

My 88 with a 302 efi has the problem with the light flashing... But I have no power loss. Just annoying @ night with that light flashing when it fells like. I'll have it fixed next summer with a 351c with a carb.

 

it looks like a 460 for me if I can not fix it this has stumped me and I am fairly good at electrical but this one is kicking me

 

Intermittent shorts are the hardest to find... good luck!

 

thanks I guess unless I can find a uncut harness then I am going to make a new one.

 

Does it happen cosistantly at a certain time or condition?

 

all the time even more when I push the gas down more 1/2 to wide open evertime but 9 times out of ten if 1/2 or less and only when I left off the gas it dies even when rolling put it in neutral will fire right back up and you have to give it gas to keep it running and then throw it into drive then take off but *** soon as you let off the gas she dies but you uplug the sensors does not have to power it should but the ****er runs like brand new no miss no nothing plug in the sensors same problem, I have replaced every sensor four to five times I even bought the last ones from ford still the same problem

 

Have you been able to check the fuel pressure when it is acting up? Have you taken a good look at your IAC?

 

I have access to a '88 f150, 4wd, that is going to be parted out if you need anything, pm me.

 

Have you pulled the codes off the computer. A flashing CEL is telling you a serious problem is occuring. Playing the guessing game without asking the computer what it is seeing and you may as well just give me your money for all the good your going to do.