I have a 1990 F150 4.9 with a 5spd. which has got me stumped. It has what appears to be a miss at between 1,200 and 1,500 rpm and can be above that sometimes. Upon acceleration it has a hesitation and comes out of the miss then starts missing again when it levels off. I have check all vacuum lines. Replaced sparkplugs and wires, cap, rotor, fuel filter, fuel regulator. Tps, Purge regulator valve, air bypass solenoid ( which were bad). Previous to this problem I had also put on O2 sensor and EGR valve. I have cleaned the Throttle body and replaced gasket there. Thanks

 

I would check the timing and pull the computer codes.

Make sure you check/adjust the timing first, so the computer is getting the right input. Then it wil guide you to whatever other issues it may have, save you some guesswork. If you don't have a manual, you can post the codes here (in the pre-97 forum) and someone will be able to look them up for you.


NOTES:

when you check the timing, make sure you remove the SPOUT connector or else it will be totally off. Also there are TWO of the markers for timing, one on each side of the engine. One of them is a leftover from a million years ago and is not the right one. I don't remember offhand which is which, but I do remember thinking the wrong one was the one you could see, the correct one was the pain-in-the-butt one Make sure you use the correct one.

Also, you can pull the codes yourself without a code reader or anything. Do a search on the pre-97 forum, there's detailed instructions.

 

Thanks for info. I will check codes again. I do have one question though. I have over 3000,000 miles on this engine and have never had timing checked. How would it get off if never moved?

 

i agree with clifford check the timing with 300,000 miles and never checked timing it can change by wear with that many miles. i would also do a compression check as you could have a valve issue.

 

Ok I have just read my codes and shows that I had code error 41 which is no Exhaust Gas Oxygen switching detected- always indicating lean. I had just changed my 02 sensor in Feb. along with my EGR valve. I am going to check my wiring to 02 sensor next. I haven't checked timing yet. The man a checker didn't think this was the problem, I'll check it anyhow. I have already done a compression test and ranged from 150 to 145lbs. I have another question also.
I had been hearing a hissing sound which I thought was coming from my coil after I shut the engine off. Not sure if that was where it was coming from, but I went on ahead and changed out the coil. The thing runs worse now than before missing all the time when under load and warmed up. Thirty five mph is all I can go and it is bucking all the time. Can't correct it with throttle like before. Cannot see what difference that switch made. There is also a wire that comes from the hot side of the coil pack and goes to a resistor or capacitor. One wire lead with a tab I assume which is the ground that goes to coil bracket. My question is should this carry resistance? I ohmed it out and got nothing. Could this also be a problem? Thanks for the advice. This thing is driving me nuts.

 

I have now checked in my Chiltons Manual and it says that with theTFI-IV ignition there is no timing adjustment. I am thinking it is controlled by the computer. Am I right on this? I have just checked my wiring to the O2 sensor and all seems well.

 

Well it has just gotten worse. Checked my codes as stated above and erased them. Checked again and same one came up. I unhooked the EGR line at the solenoid ( Man at Autozone said EVR solenoid was working ok) to see what would happen. It did run some better, but still chugged along. I also checked the TAB and EGR S/O solenoids which did click when I applied a nine volt battery to them. Not a hard click though. Had to run some places and hooked everything back up. Ran terrible, so unhooked it again and ran some better, after about nine miles it totally shut down and would not start. Had to tow it home. It sounded like it was what I call deiseling when it stopped. At this time I haven't had time to check if there is even spark. That will have to be tomorrow I've had enough today. Any help would be nice.

 

Ok Guys I have brought the dead to life. Well kind of. I had no spark so took control module off and had it tested. Dead as door nail. Put new one on and started right up. Went on test drive and ran great for about two miles, then started doing the missing at about the 12-1,500 rpm range thing again. So I'm still back to the original problem now. Anyone have anymore information that could help?

 

The one thing you haven't mentioned is changing the PCV valve. In my experience, a bad one will produce a missing, lurching sensation at around 80km/h steady...but not as violent as you are describing.

Have you checked/replaced everything in the ignition train, ie plugs/cables/dist cap etc?

 

I have checked the PVC valve and seems to be operational. The only thing that has not been replace in the ignition as far as distributor is the magnetic pickup. I was told that as long as it is running it is working, but I thought that in the 70's that Chrysler had pickups that were bad and made the engine miss. So not sure on this one. Doesn't seem to miss when idling until the check engine light comes on then will miss at idle, but also comes out of it in time. I haven't driven it enough since getting it going again to have the check engine light come back on.
Planning on doing that right now.

 

I'm still needing help. Took it on a test drive and it still hesitates when I accelerate and then starts it's missing as it levels out. After check engine light came on I stopped and took the vaccum line off of the EGR Valve. When I did that it ran fine from there on out. I am thinking that maybe my EGR valve is opening and closing quickly. Is that possible? My other question now is could one of the things be EVP sensor? That has not been changed or tested if even possible.

 

Your description is typical of two issues your engine is famous for; dirty fuel injectors or too much EGR flow. Since disconnecting the EGR solved your problem, it sounds to me like your injectors are okay (which is amazing, considering the mileage).

To solve your problem, you need to make an EGR restrictor plate, and install it between the EGR valve and the intake. Get a small piece of sheetmetal, about 1/32" thick, and use an EGR valve gasket to draw an outline on it. Cut away the metal outside the outline. Use the gasket again, and draw the top circle on the plate, as well as the two bolt holes. Drill out the bolt holes, and use a 1/4" drill to create a hole in the center of the circle you just drew. Make sure the 1/4" hole lines up with the point of the valve on the EGR. Install it and the EGR with a new gasket on both sides of the plate. This will solve the EGR miss.

 

Before messing with an EGR restrictor, you might want to properly diagnose WHY you're getting EGR flow when you should not be getting it.

Check for vacuum on that EGR line. It should only have vacuum when the PCM commands EGR flow, otherwise you will get your exact symptoms. A common failure is a leaking EVR valve that allows vacuum even when non-commanded.

Steve

 

I must say after driving it with EGR vaccum line off and warmed up it still goes into this jerking mode. I do have vaccum on the line, but it pulsates. I don't know if this is from the valve feeding this or not. I just replace EGR valve in Feb. Would it be possible that the electronic sensor on EGR valve to be bad?
Thanks for the info guys!!!

 

It's not that it's getting EGR flow when it shouldn't, it's that the amount of flow it is getting is too much. As the engine wears, it requires less EGR flow. If it was allowing flow all the time due to a bad EVR, the engine would be hard to start, wouldn't idle when cold, and would have no power at WOT.

There is a good thread on the subject here. His solution is the first post on the second page of the thread, but the whole thread is a good read.


I suspect your problem is the result of needing an EGR restrictor plate and dirty injectors. As far as the injectors go, you can have yours professionally cleaned or replaced, but first try adding a large amount of injector cleaner to an almost empty gas tank, add another $10 worth of gas, and drive on that tank for a half hour, and let it sit overnight. The next morning you should see an improvement. If you do, have the injectors cleaned or replaced. To completely solve your problem, IMO, you will need to do both the restrictor plate and the injectors.

Good luck.

Take care,
~Chris