Hey all, so after the exhaust debacle the truck has an issue still. I have had this issue since I got the truck and I cannot figure out what is up with it.

When the truck is cold it starts, runs, and drives perfectly fine with zero issues what so ever. However, if I drive it for instance 20 minutes, go to the store, and try to start it after ~15 minutes to 1 hour it will start, RPMs will go to give or take 1,300 then straight down to 0 and stall. It will do this again and again until I time it right and get it into gear, reverse or drive it does not matter then it doesn't stall. But it will run odd and hesitate for about 30 seconds then it will smooth out and run fine with no issues.

Today I took it on an hour drive, with bad traffic, and after I stopped to get corrected directions, was given the wrong address, it stalled in park. I got it to start the first time and it didn't give me any issues until I pulled into a spot at the right place where it decided to stall before I put it in park. Then after about 15 minutes it decided to do the fun game of when will it run right and you can get it out of the spot. After 3 attempts it finally let me get it going and ran fine the whole hour home.

I have no idea what the problem could be, it almost acts like it has no fuel, but it does it on both tanks, front and rear.

Any ideas?

 

I forgot to mention. There are no codes. The CEL never came on even for a split second while driving either. Only code I get is the system ok (Code 11).

 

Update:

So after I did some reading here as well as other forums I figured the o2 sensor needed to be swapped out. Bought an NTK one and put it on, the truck ran REALLY BAD, way worse than before. When I left the parts store to return the o2 socket rental I could not get it to idle at all, it took about 10 times to get it to finally idle enough to Walmart to drop off used oil, again it did not want to idle at all and took another 5 times to get it going. I then went to the gas station, and after I moved it into reverse to pull into a pump to throw a little gas int it after getting some injector cleaner/some gas it died. Then again it did not want to restart until I jabbed the throttle and dropped it into gear. While I was sitting at a light, on my way home I noticed it was hovering about 500RPM and would dip to ~400RPM, then jump to ~700RPM then back down to 500RPM, over and over again. It ran fine enough when it had some speed and felt okay, but idle and restarting issues have gotten FAR worse.

I tested the o2 sensor (heater element) and it was within ohm spec on both the new and old one. I decided to throw the old one back on and it ran the EXACT same as it was with the new o2 sensor. Would start, rev up and immediately idle down and stall. It did that 2 times, then I managed to get it to move into the driveway and it was wanting to do the ~500RPM, down to 400RPM and back to 700RPM, then down to 500RPM again.

I had the AC on and off while it was doing this stupid idle thing, no difference. Both fuel tanks have been replaced and have new fuel pump/assemblies.

Also, no check engine light or any codes, I got 10/11 again.

What in the literal H*LL is going on with this thing?

 

Maybe the Idle Air Control solenoid. Here's a good thread on it https://www.fullsizebronco.com/threa...ur-iac.206960/

 

I found my original IAC Valve and put it back on after cleaning it again thoroughly. It fired right up and I was able to get it moved to get my other vehicle out of the garage for work tomorrow. I let it idle down and it wanted to stutter some and the RPM fluctuated and it would not smooth out, and it did not stall. So the IAC swap seemed to have helped some but it is not the complete fix.

I also pulled the original TPS and noticed the ground wire on the module side has the insulation pulled back some and exposing wire, I tested for continuity on it and it was consistent, but I don't think it would be a good idea to reuse it. It also had some dirt and oil inside it, could the throttle body shaft seal be an issue and causing it to give off a bad reading, but not enough to trip a code? I also wonder if the dirt and oil leaking into it could be causing it to stick. Or should I replace the TPS since I have it off? And if I do replace it, from what I understand is I need .9 volts to 4.5 volts at wide open throttle?

I have found two replacement ones, the Motorcraft CX1228 and an NTK TH0131, which would be the better buy? I am leaning towards the MC, but the $50 is throwing me off because I feel like I am throwing parts on it for no reason in hopes it fixes my problem.

 

Here's a thread on how to test the Throttle Position Sensor. https://www.ford-trucks.com/forums/2...est-a-tps.html
Test the one that's on the truck now before replacing it.

 

Has the stop screw for your throttle plates ever been moved, that you know of?
That stop screw is mistakenly used for an idle adjustment by people.
If you decide to clean the throttle body, use throttle body cleaner and try not to scratch it up.
With your throttle cable disconnected from the throttle body, see if the throttle plates move freely.
Also, make sure the throttle cable moves freely. Check the plastic sleeve, inside the cab, where the cable passes through the firewall. That's one place the throttle cable can bind and cause the idle to hang.
If I were going to replace the TPS, after testing it, I would buy Motorcraft.

 

I tested the TPS and it was in range, .98v-4.5v. The throttle stop screw from the looks of it, has never been touched, I have not touched it either. The throttle cable is able to move freely back and forth with no hang ups or odd tough spots in it. The plates move freely with the cable off and there is no excessive play in them either that would indicate a vacuum leak. The throttle body was taken off and cleaned a while ago and it is not gummed up, just a slight but of crud I removed with a cloth.

So after I made sure the TPS was in range according to Ford, the truck now high idles on cold start fine up to give or take 1,500RPM, and once it starts to come down around 1,000RPM it stutters some and then dies out (stalls). This is with both the new and old o2 sensor, original IAC (cleaned) and TPS (cleaned/adjusted).

Is it possible that the stop screw could have moved and needs to be readjusted? Because when it would try and idle yesterday it would only hover around 500RPM instead of 700 or so where it should normally.

The MAP sensor is the original unit too, is there a way I can test this, I got one out of the junkyard to have as a spare in case the original one went bad.

 

I would test fuel pressure. https://www.ford-trucks.com/forums/1...rd-trucks.html
If the throttle plates don't bind in the closed position, and remain slightly open, just enough not to bind, I wouldn't mess with the throttle stop screw.
When was the last time the fuel filter was changed?

 

How's that TFI module doing? In 1990, they'd still be mounted on the distributor, which was evidently an issue as Ford relocated it to the driver's side fender below the cruise control module for '92 or '93. Your symptoms describe what happens the TFI module or the PIP sensor in the distributor is going out.

 

Sorry I haven't replied, was more concerned about my new job.

The fuel filter was replaced roughly 20,000 miles ago. I did that right after I got the truck due to both tanks being full of rust and the pumps being filled with rust too, so they got replaced as well. When I took the injectors out of the rail they got new seals and were re-freshened, since they had 120,000 miles on them. Haven't check the fuel pressure but I will try to get that done tomorrow hopefully. The range should be 35-40 psi KOEO for the 302 if I am not mistaken?

The TFI module is a replacement Motorcraft unit and seems fine, I have a spare in case it does go kaput. I did pull a heat-sink and TFI (off a 9th gen) from a junkyard to relocate the TFI due to Ford's poor placement of that module but haven't gotten around to re-wiring it. I know there is a kit, but $200 is a little steep.
The PIP module as far as I know is the factory unit as the distributor was never replaced. I would think if the TFI or PIP was bad it would be leaving me on the side of the road, which it hasn't when it is actually driving.

Is there a way to test the PIP and TFI module without having to take the dist. out?

 

Quick update:

I decided to go back through the vacuum lines to verify they were working since I removed all the old brittle plastic ones. I checked the TAD/TAB solenoids and could hear a slight hissing sound from the bottom of the one farthest from the firewall and it would not hold a vacuum. Is this normal, or could it be that's the problem?

 

Another:

I checked the back one and it holds vacuum no problem.

 

When you replaced the fuel pumps and filter, did you clean the tanks out?
Did you flow test the injectors? What specifically did you do to test them while they were out?
If your tach moves while you're cranking the truck, that's a pretty good indication that your PIP circuit is functioning.
If you want to test for vacuum leaks, block all the ports at the vacuum tree, except for the line to the MAP sensor and the line to the fuel pressure regulator, and see if the symptoms change.

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A couple of other things to check, after fuel pressure, are the capacitors on the ECM circuit board and the ground connections from the battery negative terminal to the engine block and frame.