alnen

87 F150 w/ 302. Posted before, but I don't think I described my symptoms well. I have a seemingly random hesitation or "buck" while driving. Happens at idle, while accelerating/cruising, and while decelerationg. I can see my RPMs drop drastically when it happens. Seems to improve on warm up somewhat. When it happens, if I push down harder on the accelerator, I can hear a noise on the pass. side of the engine compartment. Sounds kind of like a snap sound, not very loud though. It has died on me once on the road when I shifted tanks on the fly, but it was only once. I always have to either hold down the gas when I start it for the 1st time of the day, or it will stall and I'll have to restart it.

KOEO codes revealed an EGR vacuum modulator issue, but that wouldn't cause all this on it's own.

I'm thinking PIP, TFI, maybe a fuel issue? I dont have a fuel pressure gauge. Start by testing the TFI, or what do you think?

I've done full tune up, eliminating any chance of crossfire. Truck's done this since I got it, but seems to be getting worse. Thanks so much for the help!

jcirwin

Remove the vacuum line to the EGR valave and plug the vacuum line with a golf tee or something. See if this doesn't fix your problem.

dirtcrew51m

Does it do it regardless of how much gas is in the tank? The popping might be coming through the exhaust manifold. My truck almost has the same problem but I know it is related to the fuel pump.

truckie1885

So unplugging the egr vaccum line smoothed out my truck. What does this help or hurt

alnen

Thanks, ill try plugging the egr vacuum. I think I remember unplugging it before and there was no suction even while revving.

it does happen no matter how full the gas tanks are.

jcirwin

EGR (exhaust gas recirculation) was set up to mix exhaust gas with the intake charge which lowers combustion temperatures and reduces emissions.
If, after you unplug the EGR, the engine doesn't ping, then you're fine. My check engine light never came on so I'm thinking that the engine is happier, because it used to stumble all the time before.

Older engines seem to be more sensitive to EGR, and therefore is causing new issues for some.

EGR systems came into play in the early '70s, I believe. They never existed before emissions. (and engines were a lot happier!)

LobstahClaw

I dunno ... the compression ratios were a lot lower back in the day. ( lower combustion temps )

You also didn't expect to get much more than 100 K. out of a vehicle. Nowadays they're getting in excess of 250 K.

And .... fuel milage was only a fraction of what they're getting today.

Maybe the good old days weren't all that good.

It's just my opinion, but i think it's better to try and keep everything within factory spec.

alnen

Me sticking something to plug the EGR vacuum has no effect... Also, I turned the key to the on position and then pressed the shrader valve on the fuel rail. It shot out for a second, then reduced to a trickling fountain. After releasing it and letting it sit for a second, I still got the trickling fountain effect. Is this normal? Also maybe something to mention: The gas gauge stays on the full mark until the tanks about halfway empty, then bounces up and down until it finally gets to empty. Both tanks do this, and both tanks work fine. Thanks.

alnen

Tested TFI today. Had them test it 8 times in a row. Passed just fine. Just wanted to rule that out since it was free.

Since I'm getting no vacuum to the EGR, I started messing with the EGR vacuum modulator on the driver's side. The green vacuum line goes to it, so I know have the right piece. Anyway, I noticed 3 zip ties on it from PO. I jiggled the connections ever so slightly, and it almost crumbled apart. Didn't change how the truck runs, but I have feeling it's related. I may just go to the junkyard and pick up another one.

I'm still thinking there might be a fuel issue as well. I smelled the exhaust today right after I started it, and it smelled rich. Maybe a sticking injector? How do I diagnose that? Thanks.