My '91 300 Six has an intermittent miss/buck when warmed up. It cranks up easily and is okay until the needle on the temp gauge just starts to enter the NORMAL range. Then it starts to buck. Have new plugs and wires, new distributor (pickup coil, ignition module, etc). Mechanic said fuel pressure was okay (maybe that was prior to warmup) but he also said there was evidence of a lean condition in jug 6. I have tried to locate a vacuum leak spraying carb cleaner in likely spots without finding any. Have given it the vacuum Seafom treatment and run a liberal amount thru the tank for the last 2 tankfuls. The violent miss is intermittent. It will buck 4 or 5 times and maybe run okay for a while and then do it again.I have had the truck about 6 yrs and it was doing something similar when I got it (not as violent) which my mechanic remedied by disabling the EGR valve. It also had a problem a couple of yrs ago where it would cutoff at highway speeds and not restart for 15-20 minutes. This was fixed with a new pickup coil. The miss feels like an abrupt "Bump. Any ideas? Maybe a coil? Thanks Jim M

 

How hard is it to get a new computer for this model truck? My mechanic says they are hard to find but it is possible to send the existing one to a place that will refurb it. Anybody have a source for these? Anybody ever go the refurb route? He says there is an intermittent timing issue and when he eliminates the computer's ability to regulate timing the miss disappears. He says running it like that would eliminate the miss but the truck would suffer badly in mileage and performance. He had the truck for a couple of days trying to track this down and didn't charge me anything so I know he's not just out to sell parts and labor.

 

Had the same problem on my 92 f150, changed out the coolant temp sensor, and intake air temp sensor, and it went away. Not sure if your truck has both, there only like 15 bucks each. You can try both, or one or the other to see which one your culprit is.

 

I'm not sure if your 4.9l has a knock sensor or not, but if it does has it been checked?

 

Thanks for the tips. Will relay the info to my mechanic.

 

Most parts stores can get you a reman EEC for $80-150, but don't run out & buy one. Pull the driver's kick panel (beside the e-brake pedal) and smell the EEC. If it stinks, pull it out & take the covers off to inspect for signs of heat on the PC board.

But I'd just get a Haynes manual & a cheap ($15-50) digital multimeter (DMM), and follow the ignition diagnostic procedure in Ch.5 (usually Sec. 5 or 7). If it all checks out, start testing sensors, like the ECT, ACT, TPS, MAP...

And I'd get that EGR system working again. It protects the engine from burning holes thru the pistons.

Also, if you plan to keep the truck, I highly recommend the modification described in this caption & the NEXT several:

 

Thanks for the tips Steve. Will check into it.

 

Would this manual be specific enough towards my truck?
http://www.haynes.com/products/productID/161

 

Only if you can't find an OLDER edition on eBay, CraigsList, Half.com, etc. Read this caption:

 

Thnx, E-Bayed a red one.