What could be causing my truck to "miss" or studder at a high RPM? I can make it do it driving down the road with it up pretty high in gear, or sitting at the house in neutral. I thought all along it was a fuel supply problem, but a new draw straw, 3/8 line and two piston pumps later its still doing the same thing.

The miss is not that big of a deal i guess, but I am thinking if I can find it, it will also cure my loss of fuel milage and power.

EDIT - forgot to mention I don't have an RPM gauge, but the miss is between 25 & 2700 RPMs if I was guessing.

Thanks for any advice.

 

I'm sure you checked this before you went through all those parts, but hows your fuel filter?

Is your timing advanced?

 

Did you replace your valve springs? Some past issues were caused by valve float occurring when taking the engine beyond its normal 2500 RPM operating range. High mileage & age can cause the springs to loose some of their tension.

 

Yes, I've changed the fuel filter as part of my parts swapping, and I have never touched the timing.

No valve spring replacement, but I recently did have them all adjusted. Some were a little tight, but not too bad.

 

Sounds lke low fuel pressure, have u put a guage on it to see what your getting when you wrap it up

 

I have a FP gauge. It idles at 15 PSI, but when you romp on it it bounces back and forth between 12 & 14 PSI. From searching, I got mixed results, that the bouncing was normal from air getting in the tube, or that it was a result of a bad lift pump. Well, I'm on my 2nd expensive piston LP, and it still does it. I was thinking I was sucking air, but pressurizing the fuel tank showed no leaks on the factory supply lines. Since 3/8 supply line was considered an upgrade, I went ahead and put a new supply line in with a new draw straw all the way to the LP. Same results.

 

Heck, 15 psi is good!! You should fill in your sig a little. Might help others diagnose your issues if they can see what u have done to ur truck.

 

Sounds like not enough timing to me.

 

Is it worse in neutral or under load? Mine pops when it is cold because I have so much timing advance. If I retard the timing a little it quits (but doesn't run as hard).

 

I can make it more noticeable under load, due to the motor having more "strain" on it with it in gear, but its easy to do in neutral too. I planned to check the timing this weekend but the wife had other ideas. I still don't totally understand why my FP sometimes bounces like crazy through the gears, then others it barely pulls off 15 PSI.

 

Could be the Fuel Cutoff Solenoid is sticking or has a weak spring. Take it off and pull the plunger and spring out, put it back on.

 

Interesting, could that cause a loss of overall power?

 

Yes, very much so.

 

My IP ate the solenoid about 3 months ago so i did the grind down trick from the sticky to get it back going. My loss of power and fuel economy is something that's been steadily declining for at least 2 years. I know that sounds long to be trying to diagnose but its not a daily driver.

I can see where a weak spring might be causing the FP gauge to bounce to causing the fuel to cut on and off, or maybe thats a stretch, but either way if that's it I'm going to be jumping for joy!

 

It finally stopped raining so I was able to take a look at my truck yesterday. I set out to do two things - check the timing marks and remove the cutoff solenoid.

However, I found myself with was more questions. It appears my pump does not have the same timing mark on it that most of the ones I saw by searching have. Mine has a mark on it, its not scribed into the case though, but won't come off with brake cleaner either. Its aweful low on the side of the pump, whereas other pictures have the mark in the center of that section. Either way I need someone with more timing knowlege than me to offer some advice.

I've got two pictures awaiting approval that show the marks as well as how far the afc housing is from the head for reference.

I also checked and none of the nuts were loose on the pump.

EDIT- pictures added below: