Okay, I am at a loss here. My 90 f150 with straight 6 84,000 miles: started jerking on me at around 30 to 40 mph. Only does it if i am trying to keep it at a constant speed in that range. If i accelerate or let off the gas it stops. I have already replaced fuel filter, air filter, breather filter, pcv valve, plugs, wires, rotor, cap. Still the same problem. Could this be a transmission problem? I had the codes pulled and nothing came up. I thought maybe o2 sensor, but it idles fine. Have not checke TPS yet, but that is next on my list. The only other thing i can add is that every once in a while the transmission wont go into drive(maybe 3 times in the last couple of years). HELP!!!
Thanks,
Dave

 

Could be transmission problems too.

I've tried replaing a bunch of crap to hopefully resolve some symptoms without knowingwhat the problem was. I've learned to take it to a shop/dealer and pay $60-80 to let them tell me what is wrong.

 

took it in once already and they could not find anything. I was searching this forum and some people were having similar problems. Turned out it was EGR valve related. I think I may unhook the vac line tonight and see if the jerking stops. If it does then ill replace the valve. If not, ahhhhhhhhhhhhhhhhhh!!!

 

It could be your EGR valve, but I'm putting my money on your injectors being dirty. What works pretty good for the injectors is this (I've done it personally): Go to the automotive section at Kmart, and look for their fuel system additives. You will find one brand that unfortunately, I can't remember, but it comes in a gray plastic bottle, with a copper colored cap. They should have two sizes, the small is around 12 ounces, and the large is around 32 ounces. Buy 2 of the large bottles. Run your truck so that one of your gas tanks is near empty, and go to the gas station. Pour in both bottles, and add 5 gallons of gas (NO MORE THAN THAT!). Now drive it around for an hour or so, and then let it sit overnight. If your injectors were dirty, you will notice a big improvement when you go for a drive the next day. If the problem is better, but not completely solved, you can do the same thing again. If that still doesn't completely cure it, it's time to buy a set of injectors. Injectors aren't cheap, but that fuel system cleaner is, so do try it twice before replacing the injectors.

 

well, i have already run about 4 bottles through and did not notice any difference. And they are pretty expensive to replace the injectors. Anyway to do an easy test. I checked with my auto shop, and they said it would be around 300 bucks to test them all.
Seem right to you guys? Still going to try unhooking the vac line from the egr since that is free

 

You could replace them for less than that.

 

I'd check the egr and plug wires. Dirty injectors are rare with the new injectors being the no deposit type.
Alan

Edit: I didn't realize it was a 90 those injectors do clog up.

 

well i unplugged egr vavle vaccum line and the jerking is gone !!!!!!!!!!!!!!!!!! I am off to buy a new egr vavle tommorow. Hopefully dont not take me to long.
Thanks for the help.

 

aHHHHHHHHHHHHHHHHHHHHHHHHHH
Okay, got my new egr valve. Took old one off and made sure there was no carbon build up. Installed new one, hooked up vac line and the jerking is back. I also tried a new egr valve position sensor and no change. This makes no sense to me. Runs great with the vac line to the egr unhooked. Anybody got any ideas why this is happening?? I am running out of ideas. Could this still be injectors? If so, why does the jerking stop when i unhook the vac line from the egr valve? HELP!!!!!!!!!!!!!

 

Sounds like the components that control the egr are screwed up. stick a ball bearing in the line plug it back in and leave it be. EGR's are a PITA and as long as it appears to be plugged in the Emissions people can't say anything.

 

Couple of questions if i bypass this egr system. Will it affect the cats or the oxygen sensor? Will it pass emmisions testing?
I have also heard of making plates to reduce the egr flow instead of completely blocking it off. Any advantage to doing this rather than blocking it? I was even thinking of just leaving the vac line unplugged and just plugging it in for emmisions tests.

 

You need to make an EGR restrictor plate. Get some sheet metal (a no parking sign works well) and trace out the pattern from your old EGR valve, and then cut the pattern out of the sign. Where the pintle valve in the EGR meets the plate, drill a 1/4" hole. Get two new gaskets, and place one on each side of the plate, and install it between the TB and the new EGR valve.

 

Thanks for the advice. I actually made one of these plates last night and installed it. So far so good. My truck has not run this well in years.
On a side note, and dont really care that much other than being curious. What would cause a rough idle only at start up. After about a minute it is fine.

 

A sticking EGR valve or a dirty IAC solenoid.

 

my 1990 F-150 Did jerking also But it would just jerk one time. Real hard Sometimes when I was going faster than 40 miles an hour. Even after 60 miles an hour I have no clue What is causing it?