Okay, just spent an hour reading this thread, pulling the neg cable, testing with vacuum line to EGR valve plugged.
It didn't work.
I have the same exact miss at low RPM only; accelerating thru first and second, all is well. But let off when you hit 3rd while still giving it gas and the bad miss starts. I have a '97 E350 van with the 6.8 V10.
A leaky vaccum line to the EGR wouldn't be the reason though; plugging that line only keeps from air being pulled into the engine, not testing the EGR valve, right?
As for testing for this condition by removing the EGR vacumn hose, if the truck still bucks after removing the EGR vacumn hose and plugging it, then your problem will not be solved by creating a restrictor plate. I would look for another cause... a vacumn leak, clogged injectors, clogged fuel filter, etc.
But what about replacing the EGR valve? If it's not functioning any longer (stuck open or closed) then it needs replacing, right?
If the EGR is malfunctioning it may be allowing too much exhaust gas into the engine leaning up the fuel/air raitio. Pulling the vacuum line off the EGR prevents it from allowing exhaust gases into the engine. If the problem is corrected through this test, the valve is either malfunctioning or just needs a restrictor plate. If the valve is stuck open then this test won't show any improvement.
Before replacing the EGR try pulling it off spraying it with some carb/intake cleaner it may free it up and save you a couple bucks. Also eliminating problems with fuel, ignition and compressiong may help you find your problem. I went through everything three or four times before figuring out my problem was just cheap ignition components.
Understood! I have just installed the restrictor plate and am going to give it a thorough testing now. Will report back soon and if this doesn't fix it, I guess it's time to do an all-day tune-up. Getting to the plugs is not going to be easy on this van but it'll be nice to get it done!
I decided to just keep the plate in place but now my exhaust is extremely hot; I mean the pipes crackle and pop like they're almost glowing. I guess the restrictor plate is making the engine run super rich?
Well, pulling the vac line didn't help for me. I finally got around to pulling codes. Engine off codes were clear, but I did the timing check as per instructions and discovered it was only advancing 10° when its supposed to go 20° so im guessing its something to do with the dizzy. Good luck with the egr stuff.
well i just had the same problem on my 90 ford f150 5sd., but the engine was flashinga code as it was a P.I.P. code so i called the parts house and they told me it was the magnite and all in the dist. and that was the cause of my problem... so i bought acomplete new dist. and put it in and now it runs perfectly fine.
Fixed my issue. Turned out my TFI ignition module had dried up. That is, the heat transfer grease between the dizzy and TFI did. I pulled it off, and all that was on there was some crusty grease bits, and one really dry bare spot. I believe that dry bare spot was creating a hot spot in the tfi which controls the ignition which caused it to behave this way. Everybody says 'when the tfi goes bad, it goes bad', so I guess it wasn't "bad", but it was certainly not "good".
Thanks for all the great info on this board I dont post much but I do alot of reading and run across the post, I have put up with this problem for longer then I care to remember. I put the plate under my EGR valve and it runs like a new truck. It is nice to have this old truck running so good, thanks for such a great board.
Randle...how are you doing....I have that bucking prob...92 F-150 5 spd 4.9....I disconnected the EGR vacuum...nothing happened...did that happen to you and you put the restrictor plate on anyway???? The truck runs fine until it warms up...and it only used to buck a little....In the last week it has gotten so bad that I can't drive it...something is going to pop bucking so hard.....I was just wondering if you put the restrictor in even though disconnecting the vacuum from the EGR didn't work...