Hey Folks, I'm gonna bump this old post and add my problem here that I have been having on my 92 f150 with a 5.0L engine... All copper Motorcraft plugs tight and gaped to .50, Ford Racing wires not touching and routed to factory specs, MSD cap and rotor with Accel coil. Timing set at 13 degrees.

When I drive my truck around 1800-2400 RPM, light throttle, in third gear, "during acceleration which is most noticeable under load, going up hill ect... The engine seems to stumble like it is missing on all cylineders similar to the issues that other folks here have been talking about. It's not bucking but as the owner of the vehicle I notice the slight miss.

Problem: #1

I have an electric fan installed and the stock factory belt driven fan removed on my truck so there is no air flow present at the time of this test.....When I feel behind the engine, "were the air pump system plugs into the back of the heads." I can feel air flowing out of the passenger side tube that plugs into the back of the head...When I rev it up I can feel an increase in air flow. I imagine this is not normal so I ordered some 5/8-3/4 long bolts to plug the ports in the heads. I will start there and keep every one updated. Would that be a possible cause to the stumble-missing symptoms I am getting during my third gear low RPM acceleration? I'm not getting any codes. The engine has 293,000 miles on it and runs great.

Problem: #2

I have Shorty headers and a Bassasni Y-pipe installed that has a slight exhaust leak, "I can never get them to seat perfectly it seems. I can hear the leak on acceleration. So, I ordered the 5.0 Bassasni flange gasket. Hopefully that will fix that. With a combination of both issues screwing with the O2 sensor would that cause the miss?

Once the parts are delivered and when I have some time off to do these two projects I'll post my new findings.

Thanks for reading.

 

My issue was fixed with the missing-rough acceleration during low RPM...

I fixed the exhaust leak going to the back of the heads. I plugged the heads with 5/8 bolts and also plugged the Y-pipe. Removed the smog pump and used a 88.5 inch belt....Runs better...

 

I just had similar problems with my 92 f-150 replaced the fuel injector because old one was clogged from the years.

 

Had the same issue.. 91 F150 5.0... light throttle mid range rpm.. "surging"... you could FEEL it in your seat.. and hear it very slighting from the engine, but the tach didn't show it happening..... it was low key enough not to register on it.. Unplugged and capped the EGR vacuum line, test drove... GONE!~

Tomorrow I'll try the 1/8 washer in it.... I'm guessing, with 165,000 miles of wear.. the egr.. + Pvc etc.. dilutes the fuel charge just too much, at these rpm levels to run "smoothly"?

 

Pulled the vacuum line to the EGR valve and plugged it with a golf tee on my 1989 F250 4X4 with the 4.9 liter 6 and 5 speed ZF transmission.

The surging I have been experiencing at light throttle application in 2nd and 3rd gear for at least the last 15 years is gone.

No check engine light is on.

I bought this truck brand new on March 24th, 1989. It currently has 98,084 miles and has never run better. I am using smaller throttle openings and getting better gas mileage in the same driving scenarios then I was before this simple fix. I'm probably making less pollution per mile as all the unburned fuel charges from the missing and sputtering have ceased.

I have also found my truck works very well with E30. No ill effects on mileage and cheaper to buy.

Thanks to all the FTE enthusiasts who contribute their expertise to this forum!

 

I purchased my 1995 F150 4x4 4.9L in 2009 and the CEL has been on the whole time due to EGR -but it ran great. It won't pass the annual inspection here in NC with a CEL light but I don't think they ever saw it since it takes several minutes after staring to come on. Still, it bothered me enough to finally do something about it.

I replaced the EGR and EGR position sensor last weekend and the CEL went away (success) but it ran like crap (failure). After doing some research here I put a 3/4" OD washer with a 7/32" ID hole inside the EGR tube today and took it for a long test drive. It now runs perfect with no CEL.

Thanks to whomever discovered this and to those who have tried it and posted their results.

 

thank you for updating this thread..I have a 91 302 that surges ever so slightly...Ill check into this

 

Glad someone bumped this, I've been looking for a little while on possible solutions without spending a ton of $$. I had an idea it could all be vacuum related but this sounds exactly like my issue. I can play with the throttle at idle and get it to shake like me in 20 degree weather lol. I may try this block off solution but since I have to replace valve cover gasket anyways I'm going to try this guys solution first.

 

hello guys, been reading your messages and i"m having the same problem with my 92"f150 4.9. 30 to 55mph with a slight touch to the gas peddal it starts bucking ,jerking. first thought was fuel filter but when bucking starts ipress the gas peddal up to 65 or 70mph runs find no bucking lot of power. So Iknow its not fuel filter. After reading your messages i"m leaning to the ERG problem.

 

By using the tin foil method will it pass Emissons test?

 

same exact thing on my 1991, haven't found it yet.