I'm having issues with my 88' f250 w/ 460 efi/c6. It started a few days ago sounding and feeling like it was missing under load. It didn't want to rev/accelerate under load and required more throttle to maintain highway speeds s previously.

So I ran the usual checks. checks the plugs, wires, cap and rotor. I also checked the fuel pressure and the timing.

After all of that I noticed the carbon buton was missing on the cap so I replaced the cap and rotor.Then I checked/retimed the engine. And it was running fine until I test drove it.

It was driving fine at part throttle but when I put my into it it started to load up like before and then bog hard and into what seems like a limp mode. This happened twice on me in the same manor. ( I would pull the battery cable and wait a set time and it would run well again.)

Now I am unable to check fuel pressure while riving as my gauge hose is to short. But when reving it the gauge seemed to hold pressure ( I run 50 lbs as I have cam, headers, exhaust, etc.)

So with all that said is there is someone that could point me in the right direction it would be most appreciated as my next step is to start testing every sensor and the fuel pump, and checking the vac leaks.


Mods to help if needed

Shorty headers, comp truck efi cam, 50 lbs fuel pressure, dual 2 1/2" exhaust. (o2 in x pipe) engine made 250/360 wheel on dynojet chassis dyno just about 1 month ago.

 

what afpr are you running? How old is it? It sounds like you are over fueling it. If you can roll thru the rpm range versus stomping on it and it does not bog drop your afpr to about 42-45.

 

I am using a kirban afpr from a mustang it was installed when the engine was rebuilt around 15k miles and 1 1/2 yrs ago. When I was on the dyno the afrs went from 12.5-14.0 ( rough numbers) almost matching the dyno sheet from 2500-5,000 rpm.

So I'm slightly rich at idle and low rpm and slightly lean up top.

Now if I was overfueling it ould that kick it into limp mode? By limp mode I'm talking full throttle = 5-10 mph and missing bad. Btw I have only ever seen a code 11 when I checked them. this problem is producing no codes that I can tell.

 

In case I didn't mention it this set up has been running perfectly for 15k miles until now.

 

On the dyno its a steady pull. In your truck driving you can go from driving a few miles an hour and then jump on it. If this is the case jumping on it and dumping more fuel into the cylinders than it can burn is going to cause to fall on its face. What year is your truck is it maf or speed density. sorry I reread you original post again. When you replaced the old rotor did you pull the plugs and see what they looked like? they may be fouled. You may have a failing pip in the dizzy as well.

 

I did check a few plugs but not all and they looked fine. No fuel smell or anything like that. I have another set I will put in just in case. I will look into how to test the pip. I did replace the tfi with the one from before I rebuilt everything and I couldn't tell a difference.

The weird thing is it runs perfect idling and reving but as soon as I drive it and accelerate hard it loads up and falls on its face. It is to the point that after the bog it is undrivable.

 

When you are measuring fuel pressure are you doing it at the rail or do you have a gauge on the afpr like I do? For grins and giggles adjust the afpr down about 5 pounds and try again. What injectors are you running?

 

Sounds like sticky injectors, and by testing them at a lower fuel pressure you won't really rule this out, as they may operate differently at lower pressure. What did you do to the motor for your rebuild? Sorry if its in your sig, I haven't figured out how to show sig lines on IAB yet.

 

That is all that is done. The engine was completely rebuilt top to bottom. but those are the relevant changes to the engine.

I'm measuring off the test port on the rail. I can try adjusting the fuel pressure lower but my question is why after 15k miles is the fuel pressure now a problem? I have always ran this pressure sense it was built.

I quoted my OP the mods/changes are in there. Would I use a noid light to check the injectors? I have access to one. The injectors are remanufactured factory injectors with 15k on them sense reman.

 

Any other suggestions? I will be able to work on it tonight so hopefully I have an update on this thing.

 

You could pull the codes,

 

I did a KOEO test with a code reader and I got a code 11 and 31. If I'm not mistaken 11 is system ok and 31 is egr? I have the egr deleted with a block off pate and plug/egr simulator from rjminjection.

 

Do you still have a cat? I've been noticing a lot of failed 460 cats lately.

 

Here's a little chart to help keep things organized as your walk thru the problem.............from what I've read you can check off quite a bit, but please place special emphasis on fuel delivery.......

 

Yeah those EGR plugs don't work obviously since you still get a code but as long as the intake is sealed where the valve was it shouldn't be a problem. I'd say you have pretty much eliminated all other possibilities and the likely cause is a failing fuel pump, so you'll have to rig something up to test it.. either a longer hose for your gauge or maybe remove the hood temporarally.