I have a speed density 300 I6. It has some fuel or ignition issues. Let me explain.

I got the truck during the winter. There was a hesitation and slight bucking once it started getting warm under part throttle but run fine when i floored it. Sometimes it ran fine at temp but more of the time it had the hesitation and bucking. Here in KY we had a few very cold days. When driving for the first time in the morning to work, the colder it was outside the longer it ran fine until the temp needle started moving then the CEL would come on for EGR valve(I have the vacuum hose unplugged and capped right now.) I drove like that for a while and added a decent audio system in the truck. It was enough to make the lights dim and when the lights dimmed you could feel the truck "cut out." So I thought it was a grounding issue possibly. I upgraded to a 130 amp alternator and went to all 0 gauge wiring but issue was still present.

Now its a lot worse. Its very hard to start the truck sometimes and it does die on me. It acts like it is starving for fuel. I give it gas and it just stumbles all over itself. It will then run fine for a minute then just start stumbling again. No matter how much I press the gas pedal it doesn't go anywhere. It will backfire in the intake sometimes. The exhaust smells like gas but never backfired through the exhaust. I'm desperately needing to get this truck running.

I have a new fuel pump im installing tonight or tomorrow in the rear tank since its bad. (I want to yank the front tank and put a air tank in its spot)

 

Sounds like the contemporary problems have their source in the antecedents. An example: "(I have the vacuum hose unplugged and capped right now.)"

All the systems of an EFI computer controlled engine must be working properly. I suggest you hook everything back up the way it should be and then run the diagnostics (pull the codes) and go from there.

 

i have. i dont get any codes when the EGR is hooked up. I feel like its a timing issue. New dist cap and rotor, plugs, wires. Im thinking maybe the crank position sensor?

 

No codes...
Running like a turd...

Pull the PCM. Do a search on 4.9l failing PCM's. Usually leaking, blown, and/or bulging capacitors. I had same problem. Also search in the '87-'96 OBS forum. Same search. Your problem is nearly identical to mine. Mine had to capacitors that leaked and destroyed the traces on the board. $274 repair with replacement.

Search for Subford. He has a pix of the PCM location. It's usually under the driver side kick panel. That's how I removed mine. Some say you can do it from under the hood as well.

Post back with your results.

 

"Usually leaking, blown, and/or bulging capacitors."

Yup. Not an unknown or unusual occurrence.

 

Have you found anymore out on the problem?

 

The ECM/PCM issues are common enough that there are several companies that specialize in "rebuilding" these units. It's not just these trucks that suffer from the problem, it's widespread thruout the entire spectrum of automotive computers.

 

So my truck is acting a little better, however still bucking, hesitating, and a noticeable lack of power. What I have done if checked my PCM and the capacitors are not leaking, tested the ICM, and replaced the distributor. There are no wiring issue from what I see, and no vacuum leaks. There are two plugs that are not plugged into anything and I go over them in video number 1. Here are two videos. #1 is with EGR vacuum plugged in and #2 is with it unplugged and capped off. I explain a lot more in the videos but i ramble on too... I'm trying to get my truck fixed so I can sell the Mustang because my unemployed *** has bills to pay! Also timing was set at 10 degrees by timing marks on passenger side of motor. Yes the SPOUT was disconnected and engine was running them when I did.

I don’t think its fuel pressure because its in and out. More often then not its acting up but it does have a minute or two where it works fine. I do have a multimeter and I do know how to use it so if any voltages need to be tested I am capable of doing it.

#1

#2

 

Can't really tell anything specific by the vid but, A couple of things come to my mind.....still could be the vaccume actuator for the EGR valve being defective but the 6's for decades have had a known issue.....the EGR valve.....in you install a restrictor plate inbetween the EGR valve and the manifold, drilling 3/8" diameter holes for the restrictor, the lag/hesitation will ikley be resolved.

 

X two what Harte mentioned , in the video there is a check engine light, Hook all your components back up and it will be simple to diagnose .TR

 

Ready for a loop?

I've been running off the front tank since I got the truck. The rear tank would cause the truck to die or BARLEY run at all. I was driving and shut the truck off and when I went to start it and it wouldn't. You could hear it trying to fire but wouldn't. I decided to swap the 4 relays under the hood and I kinda abused the fuel tank selector switch. Still wouldn't fire up. SO I then switched it over to the rear tank and it fired right up but won't run on the front tank now. Its acting like its not getting enough fuel... Driveability is better then it has been, I just have to feather the pedal. I city driving is more pretty then highway driving...

I stunt motorcycles so I'm going to be putting the rear on airbags to assist with loading the truck. I'm going to pull the front tank out and put a air tank and compressor in its place. So the fuel selector switch will be getting removed soon so if I can go ahead and bypass the switch to run off the rear tank all the time I will go ahead and do that to get rid of a possible cause...


Also truck does NOT have a check engine light and NO stored codes since I have hooked everything I can up. When I first got the truck a few months ago codes would store so I don't think its PCM. Especially since I checked the caps and I'm a computer science major so I know what to look for with bad circuit boards...

 

In the early 90's (I had a 1990 F150)...the twin tanks had a recall on them....IIRR it had to do with the tank selector system.......it would switch but not activate the fuel pump in the selected tank....the recall/TSB should be easy to locate!

 

So now it seems like I'm tracking down a fuel issue. I don't think its the pumps themselves but something within the wiring.


I'm about to pull my bed off and I want to start getting ready to pull the front tank off... Can I just plug up all the hoses that go to the front tank? What about the wiring? I do want to get rid of the fuel tank selector switch and have just a simple single tank setup...