marktim

My 1989 five litre efi has developed a significant miss while under load if i try to hold her at 2k revs she drops several hundred then builds towards 2k revs and drops again . She idles fine and sits on 195 degrees on the temp guage. I tried looking for arcing leads which are new but nothing plus the plugs are fairly new. Any help appreciated.

Wanted33

I would start with a new set of plug wires. I had a 95 Crown Vic that acted the same way. ldled fine, but under load it missed.

Also you can look under the "1987 - 1996 F-150" section on the home page of the forum for more help. There's a lot of good folks there that own the same generation truck as you. Good luck.

marktim

Thanks for that I'll try some new wires. I'm hoping it's nothing more serious like a sticking valve.

marktim

Would a cracked distributor cap or maybe the contacts being worn inside the cap cause a miss under load ?

Wanted33

While you are in there, may as well replace all those parts. Stuffs cheap. Plus, if Marvel Mystery Oil is available in your area it may help to run a few tankfuls with it blended in the gas. That stuff is great. If it's not, a premium brand of fuel line/carb cleaner will help.

Also, if you're not entirely sure how old the plugs are, I would go ahead and replace them also.

marktim

I'm leaning towards plugs it just hasme puzzled why such a big miss at 2 thousand revs but it idles smoothly.
I only replaced the plugs three months ago but I guess one could have gone bad.

Wanted33

Since you replaced the plugs a short time ago, they should be OK. More than likely one of the other things is the culprit. Those old engines aren't as complicated as today's engines. Plug wires, and distributor cap should fis her. And, I higher recommend a fuel line cleaner. That could help clean the throttle body, and injectors.

marktim

I have a feeling it's got something to do with the erg valve. I cleaned out the body of the valve and the miss l have is more like a miss when you have a vacuum leak. I think since cleaning the valve it's now not opening and closing properly.

marktim

Found the answer to my miss at 2 thousand revs .It turned out to be the erg valve I had cleaned it thinking i was doing the right thing but in doing so i must have got the valve or whatever the part may be called from working properly and after a pushing the valve up and down a few times it seems to have fixed the problem. I hope this may help someone who has an engine that idles great but seems to have a miss at higher revs.