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-   1987 - 1996 F150 & Larger F-Series Trucks (https://www.ford-trucks.com/forums/forum28/)
-   -   302 missing under low rpm pull (https://www.ford-trucks.com/forums/13959-302-missing-under-low-rpm-pull.html)

cwmerc88 01-25-2002 08:52 AM

302 missing under low rpm pull
 
I have a 1990 F150 with the 302. It has a miss that no one can seem to find. Have replaced everything known in the electronics (except for the computer), plugs, wires, cap & rotor, igition module, pick up coil, coil. I have replaced tp sensor, egr valve knock sensor, relays, checked fuel pressure, vaccum, move timing around, all things that can be replaced has been. The truck will run fine sometimes, then on somedays it will miss and jump when the motor is at a low rpm and you are giving it a little peddle to speed up. Its like it miss fires in one cylinder. I am stump, ford had the truck could not find what is was doing kept it for about 3 weeks. Also I have moved the plug wires in every direction away from each other. I have heard that on these models that the pcv valve located in the back of the intake on the #8 cylinder runner has caused problems, moved it to the top port. Please can anyone help or have suggestions?

MrPleasant 01-25-2002 12:08 PM

302 missing under low rpm pull
 
Well, if you find out what the problem is, please do tell us! I have a 1991 F150 with the 302 and I am in the middle of replacing everything in sight to figure my issue out. I have search this board and taken some advice, which has helped, but has not totally solved the problem. My truck runs fine for the first 5 minutes when it is running cold. But, as soon as the temperature rises, I experience the same symptoms as you.

I'm still working it.... will post a solution once I find one.

MrPleasant :-X20

stevieray 01-25-2002 02:07 PM

302 missing under low rpm pull
 
Another truck with a miss, eh! Seems like this is a very common problem with the 5.0 motor. My truck had a miss that I finally solved by moving the PCV hose from the back of the intake manifold to the middle where all the vacuum lines connect. I have a 5spd. trans so there was a spare connection on the tree which I assume is for the auto trans. I immagine that you could tee into anoter line if you don't have the spare connection. I spent a lot of time and money doing the "normal" things like plugs , wires, fuel filter etc. but it was the hose that did the trick. Give it a try, all it will cost is a piece of hose but don't forget to block the old connection off. I just used a small piece of hose with a bolt in the end as I didn't have a proper nipple cap. Besides, you can't see it unless you look for it. Post your findings if this works or not. I am curious to see if this does infact cure a nagging 5.0 problem.

UncBob 01-25-2002 07:03 PM

302 missing under low rpm pull
 
I am having a similar problem and Ford said it was the torque converter but I had just had the tranny rebuilt.
It is in a garage as we speak for another analysis.
I will keep your fix in mind.

BTW
What do you think was the reason you had to move The PCV Valve ?
Maybe the line feeding it was clogged ?
What else would make sense ?

cwmerc88 01-25-2002 11:20 PM

302 missing under low rpm pull
 
I have already moved the pcv valve it helped a little but still it is doing the same thing just not as bad.

shotgun 01-26-2002 07:44 AM

302 missing under low rpm pull
 
Chad, My Dad had the same truck (his was a 5 spd 4x4,standard cab)with the exact same problem. After a full tune-up when cruising up a slight grade the engine would ping. When floored the truck would rev and pull strong like a mustang right up to 5000 rpm. He finally had the engine on a scope at the Ford dealer. It showed a breakdown in just one of the new plug wires. With a new wire the pinging stopped. This might not be your problem but the symptoms are dead on. New parts these days aren't always the best. I just had my first break down on the side of the road. An AutoZone timming belt snapped on my Ford Escort wagon with 19,400 miles on it. The belt should go 40 - 60,000 miles. I am lucky the valves and pistons didn't hit. The belt had a clean break and inspection showed rubber seperation at several cogs. Deffinatly defective. With todays high energy ignitions it doesn't take much of a break to lose some ignition power to the sparkplug. Invest in good plug wires.

Side note. That truck was rated at 180-185 HP. I came back from overseas in 99 and picked up 96 F150 Ext cab 300/6. He liked the cab so he bought a 96 fully loaded 302 automatic. Don't know if it was the automatic that made it seems slow, both had 3.55 gears. 96 at 205HP seemed much weaker than the 90 with 185 HP. He now has a 1998 F-150. Looking back on my situation? I wish I had my Dads 1990 F-150! Enjoy your truck now. You will miss it in the future...

Good luck with the ignition miss.
Chris



UncBob 01-26-2002 06:06 PM

302 missing under low rpm pull
 
Just got mine back and seems OK so far.
Tranny shop sent it to a repair shop
They had to clean out where the EGR valve installs .
Said they see fairly often.
Let's hope so

mavman 01-26-2002 06:17 PM

302 missing under low rpm pull
 
yea, my 95 does the same thing. Misses under a slight load, like one cylinder misfires. I'm gonna try moving the pcv to the middle, maybe that will help. It also seems to be better when the air is cold, worse when the weather is warm, but that could be cause I'm shivering:-X02

I sure would like to know how to cure it, if any of you knows a solution it would be awesome!

bjoern 01-27-2002 07:52 PM

302 missing under low rpm pull
 
There was a thread here recently that said the symptoms you describe are from the computer being unable to compensate for engine wear and EGR flow. Most 4.9 and some 5.0 would experience it, they said. People recommended to restrict the flow from the EGR valve by a spacer with a smaller hole in it:
https://www.ford-trucks.com/dcforum/DCForumID39/2279.html



UncBob 01-28-2002 07:03 PM

302 missing under low rpm pull
 
Well I put my 5.8 through all kinds of engine conditions etc and she is running great
So I guess that fix of " cleaning out the EGR entrance passages" was the solution:-X20

pickupman 01-28-2002 07:36 PM

302 missing under low rpm pull
 
My 92 with a 302 had similar symtoms at two different times and were two different problems. It would run fine until I would get to cruising speed and in overdrive, if I would lug the engine down enough like pulling a hill it would start missing. The more I put my foot into it the worse it would miss until I would downshift then it seemed to clear up. That time it ended up being a bad gasket under the plenum. It was sucking air between the top of the intake and the bottom of the intake plenum. NAPA sells this gasket for about $5.00. One other time I had a problem with a miss it was almost the same symtoms, except when it missed it pinged like I had cheap gas. That time I found that #7 and #8 plug wires were too close together. You have to make sure that these two are apart from each other, #8 fires right after #7 and they are right next to each other. 7 was cross-firing to 8 and causing 8 to pre-ignite. Then the knock sensor would pick up a knock and retard the timing causing my truck to fall flat on it's face .
I hope that somewhere in all this you find something that might help you.

cwmerc88 01-29-2002 08:10 AM

302 missing under low rpm pull
 
Just wanted to thank all of you for help and suggestions, Tried all and still no luck it is not as bad but still its there.

Electric1 01-29-2002 10:43 PM

302 missing under low rpm pull
 
There is one more place that I have seen the 5.0 engine missing at, it was the distributor shaft, The distributor shaft gets magnetized from the power and ground that powers up the pickup assembly, it is esentially like making a magnet, apply power and ground around a field or steel and it will magnetize over time, I have seen this three times, 1 car and 2 trucks, you can look and replace all you want to no avail. The first time I saw this, I used a spark tester and installed it at each sparkplug tower at the distributor cap and started the vehicle and watched each cylinder fire but yet had a steady engine miss, by using an AVERAGING DC VOLTMETER you can test for this, the top wire at the ignition module is switched by the pickup, it is called the PIP signal, (pickup ignition profile), this is fed power from below the top PIP wire but anyways this signal must be reading 50-55% duty cycle, which by the math, lets say you have 14 volts in your ignition system, measured at the battery with the engine running, 50%=7.0vdc, 55%=7.7vdc. So if your voltage running = 14.0 vdc the you need at the PIP wire 7-7.7 vdc averaging. (math 14x50%=7, 14x55%=7.7) By backprobing the top wire at the ignition module with voltmeter in the averaging dc volt mode, start the engine and look at the voltage, if by the math your specs. are not here then replace the distributor, now one more thing, the reluctor inside the distributor is a non ferrous material so it will not be magnetized, it is the shaft causing the problem. So first measure the voltage running then do the math. Hope this helps someone. Electric1

noremac19 01-30-2002 12:10 PM

302 missing under low rpm pull
 
I had the same problem with my truck. I was running ngk's and it ran like crap,1000rpm to 2000 it sputtered. I changed plugs to cheap walmart autolites, and it works perfect now. Hope this helps

MrPleasant 01-31-2002 09:37 AM

302 missing under low rpm pull
 
Well, I have changed my plugs, wires, TPS (which I know was bad), restricted EGR with 1/8" hole, new distributor cap, rotor, looked at vacuum lines for obvious breaks, checked and set ignition timing at 10 degrees with spout removed, replaced TFI module, and now have a new MSD coil. Still missing when the engine warms especially when first moving from stop on a slight grade. It will knock if I punch it. Running out of ideas..... I do have fairly expensive fancy plugs in the thing.....may switch over to the cheapo autolites to see if that helps. I may also think about retarding the timing some.

:-X09


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