Truck: 1994 F350 CC 4X4 Dually (Conversion)
Engine: 351W - GT40 Cast Iron Heads with bigger valves installed. 5.0 HO (Mustang GT) cam, 1.7 Crane roller rockers, long tube headers
Engine Control: stock SD (not MAF) with stock TFI, distributor, PCM and coil.

Problem: It runs great when 1st started up (no problems). After it has ran for about 5 min (reaches operating temp), it starts to have problems.
-Loping idle while in drive (dies sometimes)
-Loping idle in Park, but not nearly as bad (does not try to die)
-Hesitates during acceleration
-No hesitation if you don't accelerate fast
-"bucking" "jumping" Hard misses when accelerating with WOT (wide open throttle)

Parts that have been replaced:
-TPS
-coil (used)
-TFI (used)
Tasks Performed:
-cleaned the distributor rotor
-checked the spark wires for arching
-disconnected the smog pump

None of these actions nor part replacements have corrected the problem.

 

Are you sure that the cam that you put into the engine is SD friendly? I'm not too big in that department but i've heard that they can wreak havoc on how the engine runs because of the vacuum is erratic if thats the case. If not it sounds like a sensor is out of spec after it comes out of its closed loop warm-up. Maybe the intake air temp sensor or the coolant temp sensor (not the one wire sensor for the gauge on the dash either). I've heard if these, or other sensors for that matter, go out of range they can throw your timing and fuel mixture way off and cause problems. Hopefully someone more knowledgable can chime in and help out too. You can go to http://www.fordfuelinjection.com and pull the codes. That might help out a bunch. Post them back here and we can see if we can help.

 

Actually the cam and rockers are SD freindly. The SD system does not like a cam with LSA less than 14. The truck has ran fine with this setup for about a year and half. This problem is newer than the engine mods.

I have not checked the codes yet, because the check engine light has not came on. I swapped out the TFI and coil, because when these components get hot they fail. The sensors you are talking about might be the problem.

Do you have anymore info on sensors that can fail when heated up?
Vacuum is something that could be an issue, but I did not think vacuum would be a problem only at operating temp. Is that possible?

I have been thinking it was ignition related, so I have not chased sensors nor vacuum yet.

Something else I noticed. When traveling on a rough surface (my driveway is a dirt road 1/2 mile long), pot holes cause the engine to miss for a second. I think it is a miss, it sounds like it. This happens when the engine is cold or hot.

 

Check your grounds and plug wires for the pothole situation.
Check for codes anyways.

 

Anyone have some information on these sensors that could be giving me problems after the truck is warmed up?

 

PIP (Profile Ignition Pickup) is my guess. It's the Hall Effect sensor in the distributor. This is what sends the signal to the TFI to fire and the injectors to fire. Very well known cause of warm drivability issues. It ranks right behind the TFI in problem source. It is replaceable but it takes some tools and knowledge.

 

Check for Fuel Pressure? Sometimes it helps to take off the fuel feed line in off, hook an air gun to the end and blow everything back into the tank. Can help unclog pick up screens that can sometimes become gunked up.
VT247

 

Would a bad PIP cause the engine to mis-fire while driving over hard bumps in the road?

 

A bad PIP causes all sorts of wierd vaiations in running. lol. I had one that worked perfectly for weeks and then would just cut out on you for no reason and leave you in a death coast on the interstate. That's no fun. A lot of people replace the distributor to change the PIP but a lot of times you end up getting a bad one back in its place. The auto part store bench tests them and if they show good, they don't change them. If they come across an intermitant one that tests good (like I got from them three times) they seem to package them back up to sell. It's really aggrivating. I finally broke down and bought the sensor and took apart the distributor. It normally takes a press but I was able to do it without one. I'm not sure how the PIP reacts under a vibration or shock though.

I would still check the codes. The computer will still store codes without showing you a check enging light at all. This might lead to your cause of the problem. I also second checking the all the grounds and make sure that your battery is secured and not arcing on your hood when you hit a bump. The two sensors that I mentioned are pretty easy to get to and don't cost too much money. It might be worth trying to obtain the values to ohm them out or just replace them to rule them out as a cause. Again the computer might have stored a code from these acting funny or reading out of spec. I think that I have heard of the MAP acting funny after the engine was heated up and heat-soaked it a bit, but I believe this is rare. Not too sure on that one though. Let us know what you find!

 

This morning the engine was running bad right off the bat. I only use it once a week, but it was worse at startup this week then last week. I have a press and a ford code checker. I forgot to mention that I did replace the tps (brand new) and the IAC (used). I probably should disconnect the battery and let the computer reset. I will read the codes 1st. I also have a 94 F150 with MAF. I am going to take the MAF system off of it and put it on my F350........ That is in the future though.