94 f150 5.0 stumble around 1500 RPM
 

New guy here with a problem. Any help would be appreciated. My 94 F150 has a sort of stumble at around 1500 RPM. I had a reman engine installed, the old one used oil and just wasn't performing good. The stumble was there before the engine change and I actually thought it was a tire. I was wrong. I have no codes or CEL. I have replaced almost everything except the MAF and O2 sensor. It has a new PCM, Distributor, plugs and wires, EGR and regulator and EGR sensor, TP sensor, injectors, and coolant sensor. I don't have a vacuum leak. I can duplicate the problem at idle by bringing up the revs to about 1500 and the engine shakes. I have the EGR blocked off at the moment but it gets alot worse if I hook up the EGR valve. Is this a wiring issue? I really want to get this fixed, this is my main daily driver. I want to restore this truck but don't want to go any further until this problem is fixed. Help!

you don,t suppose the timing is off or a valve sticking ? check the timing with a timing light ! also hook up a vacuum tester to the engine to see if there are any vacuum leaks, it also will tell you if there is a valve sticking !

Thanks for the reply. There are no vacuum leaks and it was doing this before the engine swap so I'm thinking it's not a sticking valve. I set the timing so I believe it is correct. I'm was just wondering if it could be a wiring problem or something like that. I was hoping somebody has seen this same thing before.

You didn't mention it, but have you done anything with the fuel system like check fuel pressure and/or change the fuel filter?
It would probably be a good idea to check the fuel pressure especially considering all you had done and it should perform better than it is.

I changed the fuel filter but have not checked the fuel pressure. What should it be? I will try and check it this week.

i belive fuel rail pressure should be around if not right at 40 psi

It is important to observe the fuel pressure at the time the problem is occurring.

I'll check it this week. I'll have to get a gauge. Thanks for the replies, this is something I've been dealing with for about 6 months and hope to find a solution soon. I'll let ya'll know what I find.

bumped

Thanks for the bump. I still haven't had a chance to check the fuel pressure. I did replace the MAF and O2 sensor but that didn't help. The other day when I was driving home it started running really rich and shaking to the point that it felt more like a tire coming off than an engine shake. I turned of the OD and got the revs up and made it home. Right before I got home it actually cleared back up. the CEL came on and I had a 157 and 173 code in KOEO. So I replaced the MAF and O2 sensor. I still need to check the fule pressure but I will be out of town this week so it will have to wait till I get back.