Hey all,

So it seems I've run into a problem with my truck recently, probably for the past month its been happening every time I drive it. So here we go:

When the truck heats up after driving for a bit it will start to bog under acceleration/load. It seems to be a misfire for the most part, but sometimes it seems to actually cause the truck to start lurching hard. It happens every time I drive it, but when the truck just starts up it will usually run perfectly when I accelerate hard.

I'm thinking fuel delivery issue, so I have been messing with everything and testing as much as I could. I know the fuel pump is fine, and the fuel pressure regulator is new (I replaced it when the problem first began and the pressure read high, but the problem continued after I replaced it still). I've checked my TPS, as well throttle body gasket. EGR, EGR solenoid, and EVP sensor are all good. I've dumped sea foam in the engine hoping it would clean injectors if they were clogging. Haven't noticed any blatant vacuum leaks.

I have noticed a vacuum leak noise coming from brake booster, but that wouldn't cause this, could it??

Everything else on my truck seems to be fine, and I can't seem to pinpoint the issue. Thanks in advance!

Info on the truck:
1989 F150 4.9L L6
M5OD 5 spd
smog pump delete

Trouble codes:
34 - EGR something or other
44 - Thermactor (I blocked the line off)
67 - Clutch position sensor
87 - Fuel Pump primary circuit
96 - Fuel Pump secondary circuit

I have been unable to find the cause of codes 34, 87, and 96 - every component for EGR and fuel pump system seem fine, and I have not noticed any ground issues along the fuel pump wires.

 

whats fuel pressure? what about when under load? have you checked vacuum at idle?

 

fuel pressure was right around 50 psi idling iirc, I have no way to test under load though. As for vacuum, you mean on the fuel pressure regulator? If so then yes and it holds vacuum.

 

before I replaced it, the pressure was reading around 75psi under the same conditions

 

Could it be an ignition issue? plugs? plug wires?

 

I was thinking it could be, but all my plugs are getting spark at idle, I used a spark tester for that. That at least shows the wires are doing their job. There's no way that I know of to see when the truck is under load, any ideas for that?

As for the plugs themselves, I haven't gotten around to checking them yet because I've been swamped with school recently, but they aren't very old, I replaced them at the beginning of the summer, around early-mid May. I even paid extra for platinum spark plugs instead of the copper.

The truck ran fine for a 1,500 mile drive twice over the summer, from my university back home and vice versa. Once I got back for school the issue started randomly and hasn't stopped. It's almost as if its behaving as if I shifted into too high of a gear, just because it sounds like there's a misfire.

One thing that could be helpful, the problem started around 24hrs after my friends and I were doing some top speed runs with our trucks near his property. If that could have caused something to go wrong maybe the info will help.