1990 300 I-6 with E4OD.
I have a few more posts in the past few months about this continuing problem, and dman I hope someone can help...

Symptoms- Several starts in the A.M. to keep it running, when it stays running it is rough at idle, and you can see the engine shake. At highway speed it runs great if I am not towing. If I tow it has low power and frequently you can hear the valves. I am only towing a 19 ft boat on a trailer, max gross weight is under 4200 lbs. I have a 3.08 or 3.11 rear end, I can't remeber which but ut wouldn't matter. I ma rated by Ford to tow over 5000 lbs. At idle I can manually open the throttle under the hood, it smooths out but you can still see some shaking of the engine. The only code I am getting is a continuous memory code 62 [torque converter not locking up]. I think this ais a symptom caused by whatever the engine problem is. I get an 11 for KOEO test, and no codes at all running.

What I have done- Last 3 months, I have replaced front fuel delivery module, egr valve, throttle body gasket, intake manifold gasket, TFI module, ACT sensor, coolant temp sensor, throttle position sensor, air filter, fuel filter, wires, cap, rotor, fuel pressure regulator, thermostat [don't ask why ] and PCV valve. I have cleaned the IAC valve,installed an EGR restrictor plate,and sprayed every seam and hose looking for a vac leak.

The only possibility in my feeble mind is a clogged cat. My plan is to cut the rear cat out and replace with 2.5 inch straight pipe. It sure seems like a vac leak, though. I am totally stumped otherwise, and I need some help from some of the 300 I-6 gurus out there...

 

I also replaced the coil...

 

Wow, ssounds like a real head scratcher, how are the plugs lookin? Before you go and cut off that cat get a hold of a pressure gauge or someone that dose, drill a small hole in the exhaust pipe right before the catalytic converter. Install a temporary hose fitting and attach a long rubber hose and a 0 to 10 pound pressure gauge. With the gauge inside the car, drive up a hill or accelerate and read the pressure. Normal is 2 to 3 pounds, restricted 4 pounds or higher. The drawback to this method is the small hole will need to be welded shut after the test; a minor job if you have a welder.

Why did you install the egr restrictor? How's the fuel pressure looking,ignition timing?

 

Pulled the plugs tonight, actually. They were in fine shape. I cleaned, re-gapped and replaced. It wasn't really necessary, but it was something to do since I was pulling them anyway.

 

Same problem, '91 F150, 4.9L, 161,000 miles. Nobody has the answer, or at least the "right" answer. No codes. Tired of replacing parts.

 

Clyde- The intake manifold/ throttle body gasket are goo places to check. The stock gaskets suk, and I noticed a big difference once I replaced mine, until something else screwed up...

 

Installed the restrictor because of what I read on this forum indicating it would increase performance. Fuel pressure should be good with new pump, filter, and regulator.

 

when its at idle, do you smell alot of gas in your exhuast?

 

No, not at all. I would suspect a bad injectoor plug, or soemthing else making it rich, if I smelled gas or if the exhaust was blue, but no dice. I pulled one cat, and it has more power when I punch it, but the same low idle problem.

 

Your truck is definitly running lean. When you say that it runs good at hiway speeds and then has loss of power when towing tells me your leaning out. Check the fuel pump pressure? If the pressure if Ok, make sure there arent any kinked lines that would restrict volume or flow. On the big diesels we send injectors to the pump shop where they are cleaned and tested for spray pattern and fuel flow. I dont know if thats possible on gas motors but I would suspect clogged partly clogged injectors considering all the work you have done so far. When you said that you can hear the valves I'm guessing you mean its pinging, thats also an indication that its leaning out.If you have access to a handheld computer run the truck hard while towing and watch the O2 sensor readings with your foot to the floor. If the readings go lean as the truck starts losing power this will confirm the problem.

 

See how much vacuum you have at the map sensor. If it is below 17 or 19
(I can't remember which) the vacuum is to low and will cause this type of problem by causing it to go into open loop.

 

Mine acts a lot like yours. You are running too lean. I found the flange on the intake manifold by #6 cyl cracked off and leaking. Took it off and am getting the tab welded back on. before i took it apart, the old wd-40 trick really smoothed out the engine at idle.

 

Thanks GWTarpon. I pulled the TB and found the worst looking gasket I've ever seen. It had "melted", burnt, and warped and the top and was in pieces. Cleaned the TB and installed with a new gasket. Cranked and ran like the POS it is. Then yesterday after letting it sit a week it cranked right up and jumped into high idle like it's supposed too. Scared me at first, I thought something had stuck and almost shut her down. This morning I had to crank it twice before it jumped into high idle. But it's better than it was, and runs better too. What else should I be looking/checking for? It still seems like something isn't quite right, although it's much better than it was. Thanks again.

 

Clyde- The hi idle that scared you was likely justthe computer. It has to re-learn itself after a significant change toi the system, like fixing a major vac leak, or after the battery is disconnected for more than a couple of seconds. Take it out on the hiway and run it like a bat out of hell; the computer will adjust itself, you will have fun, and it will be your way of extending your middle finger to the hi gas prices !!

 

Thanks. I already stick my finger out to gas prices too much now. It's back to cranking the way it was before the repair. Would a head gasket do this? It runs fine when warm and I'm not losing any water that I can tell.