1980 f150 5.0 c6 runs bad under load.
 

I really appreciate this site. If nothing else, an excuse to stop, grab a Stella and come post a Question. I'm so exasperated. I'll ,make this thorough and short and sweet.
Started a week ago when it developed a hard miss. It's the kind like from a pickup loose connection in a distributor. It only happens when waiting at a light with foot on brake. Keep in mind it's a new distributor, with new plugs wires and fuel filters, new firing module, new coil. New vacuum lines, new booster diaphragm. . I can throw it into park and the idle picks up there is still the feel of something So, I started thinking it was a pvc. Replaced. Same symptom. Pulled the hose from the EGR and plugged it. BOOM...I sat there in my driveway and went back and forth drive to neutral and drive to Park Reverse to neutral reverse to park. Over and over. It did not miss. I found the problem, I thought. I figured the EGR was getting stuck in the open position and running poorly from that. With EGR vacuum line plugged it purred. I took my EGR in with me and life time warrantied a new one. I installed it and it still has a miss. Only in drive or reverse. So before I pulled the EGR hose loose and plugged it I messed with the rich/lean because it only happens at idle, So after replacing egr I got 2 cans of carb cleaner and planned to clean the carb out good and could check for vacuum leaks None detected. totally removed one by one TVS, Purge Valve Re ran a new brake booster hose to a new diaphram.to a new PVC. Sprayed carb cleaner through pvc hose. Through carb bowl, vent and pvc nipple. Saw a spark at coil clip connector and coil post (+) I believe. It was shorting and arcing steadily for awhile. Could that new coil be bad? There are just too many possibilities.
Started looking at modulator and vac line looked connected I pulled it off to check for fluid. BOOM. Modulator hose full of fluid. Relief short lived. I have 3 or 4 old modulators They were known toi be good when I removed them Replaced modulator and spilled some fluid (forgot to put a pan) Should the fluid be pouring out that high? It is any way new modulator, new hose end. I figured that was it, but, NO. Same exact symptoms. Heavy miss under load like the choke is on. (verified choke working properly . Choke cap is set to 4 lean (clockwise to close early) Is this possibly a culprit? Could it be the new dizzy with their pre installed pick ups? When that tranny fluid gets in the vac line I'm sure the hard steel tubing has some vapor of tranny fluid but it shifts so the vacuum signal is getting through. I rechecked vac line to verify modulator was good. There was no fluid in new line. Idles really good in park. in reverse or drive with foot on the brake it misses hard like its going to die. Likely, that tranny fluid is all through most of my vac lines and probably caused my egr to get sticky. Now this new one will be sticking too. Is this a case of needing to get some Seafoam? Take it out and try to blow it out? Thanks for any suggestions I've tried idle leaned idle rich. I think by writing this I just figured out it's those passages. Thanks Again. 2150, C6

If I read that right, the problem goes away with the EGR capped? EGR should only open during acceleration. So it should be closed at idle and wide open throttle. Does your vacuum lines match the emissions sticker under the hood? I've never had much luck testing for vac leaks with carb and choke, or anything else. Try replacing the lines going to the EGR, and any caps you may have. Assuming everything is routed correctly. Pics if you've got them.

Thanks for replying. Yes I've re-ran all of it correctly now. Its tranny fluid in my intake probably. I'm going to try to clean that out.

Pull the EGR line back off and plug it. Runs better again like it did before?

I'll try that tomorrow when I'm trying from scratch. I cleaned all tyhe vacuum passages good, pvc hose, the tree, basically anything that would pull vacuum I sprayed. It idled real nice and after cleaning out lines went from 15.5 on the vac gauge to 17.5 and now is stable at 17.5 but it's surging even in park, now. I can hear it surging slightly roughly about the same polace it would miss hard when in park. I'm starting to suspect a bad distributor. It's two weeks old. The coil is the same age and I'm not competely confident it's holding up at high voltage under stress.

Well, I tried puilling and plugging the egr again-not a bit of difference. Still doing it. I'm installing new plugs and then will pull carb I guess. I'm pissed and frustrated:(

Im not familiar with your truck and engine. It reminds me of what a '92 ranger did to me, it had a bad throttle position sensor. It also had an intake leak and a short in the wire harness. I'm sure yours isnt a tps or a short. But it does feel like something isnt regulating like it should. Now, im no witch doctor and this is all still like voodoo to me. But. Did we rule out egr? Have you put a vacuum tester on it to make sure it actuates? It could have finally stuck completely open. Other things that come to mind. What distributor do you have, could it be an advancement issue? Or, is it time to rebuild the carburetor? With any luck some one more experience will come along and tell me if I'm anywhere close.

Just finished putting 8 new motorcraft plugs in. Found 2 that looked fouled :-jammin Hope fully that was it. But I'm skiddish now to think that could actually b e the end of this. Just wanted to be sure. Also, the lean/rich was much to rich. That's been corrected now. Does anyone know if the delay valve is needed in the egr vacuum circuit and what that penny trick is about.

You let her idle yet? I assume since they put the delay valve in that it's important. Having said that I can't remember it's exact function, my emissions book for my year model didnt seem to mention it, or I couldn't find it. My truck is supposed to have one. So I'm not sure why it wasnt in my book. I have read about it, and I will try and find where I found that information. In the mean time. Shootin from the hip here. My damaged brain thinks the egr is only open during acceleration, up to WOT, something like 32, or 3500 rpm, cant remember the exact number. That keeps her from idling rough, and keeps you from losing power when you need it. I think. 0 confidence on this. So then I assume when you lay on the throttle, the delay keeps the egr from opening at the same time, and maybe messing up the ratio? and, brain feels better about this one, keeps the egr from activating for every little variation in vacuum? Pretty sure I made some of that up though. Literature hunt commencing... now! Where are all those emissions experts....

I'll have to go through the book again. Best I can find on here is it prevents erratic behavior when rapidly changing throttle position and maybe preventing misfires from too much exhaust gas recirculation. But that's paraphrased from a theory and no one confirmed it in that thread.

All the book says about delay valves, is they prevent sudden application, or removal of vacuum, or both. So it allows smoother operation. looks like flow is both directions if both sides are same color, flows from white to colored side, and colored side to black. Not sure what type yours is, looking at my sticker it looks like mine prevents the egr from closing suddenly. Which I think would cause a backfire? Wish one of the all-knowing gray beards would show up and set us both straight. All I can tell you for sure is it should smooth out operation of the egr, as to what happens when you don't have it? Your guess is as good as mine. Wish I were more help.

https://dogandlemon.com/articles/own...l-egr-problems its diesel specific, but should apply anyway, worth a read. The delay valve may also act like a dashpot, and prevent the egr from closing too soon, for better emissions.

I just re read all posts. EGR seems to be ruled out. With any luck it was plugs and you're good now. Seems like a carb issue, idle settings. What choke does your carb have? Also, did a generic internet search, pretty weird out there. Different vehicle styles were having the issue, so that changes a lot, but suggested culprits were electrical load, which makes me think alternator, and the other was torque converter.

Sorry to hammer your thread with responses, my brain only works in fits and bursts.

I was wondering if maybe you just like talking to yourself.

j/k ;)

That does look a lot like how my thoughts run, so maybe talking to myself some. Looking back at those posts I may have done more harm than good. Who around here is the go to for emissions? Maybe someone with more skill than I can drag them here and untangle all those knots I tied?

Thanks for those fits and bursts. I am about to go down and find out. I had the rich too rich and fouled 2 plugs and with two fouled plugs it would run like it did,. I'm hoping but also noting electrical load tells me my suspect heater could be linked at least. It's popped apart and the levers and spring gizmo. It's a 2150 carb with a auto choke plus assist. It's always a endless trial to adfjust the index because with mirror glasses and flashlight I still cant see if it's on the notch when doing fast idle adj. Will post what I find but want to double check. Does anyone know whether the purge valves can be hooked up backwards.?