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Hey , I'm having issues with rough idle and bad pinging on my 94 f250 with a 351 . I took it apart to fix a coolant leak at the intake manifold and timing cover . I had to replace the distributor as well due to worn out bushings ,also replaced timing chain since it was apart . Took it for a test drive and it ran like crap , had good power it felt but rough and pinged a lot . I triple checked timing and it's bang on 10*advanced DNS yes pulled the spout connector . I did notice a small arc when replugging in the spout . I pulled some codes and tps low voltage came up . Checked the voltage at the tps and got 0.05 and when I open the throttle it goes down to 0.02 volts ? Also checked a few other sensors and there return voltage is also 0.05 . The power coming into to them is within spec though ? I replaced my tps and still the exact same thing ... Not sure if it matters but the distributor I put in is listed for a 96 . All the parts people here said that the 94 has a cast iron gear and the closest year with a steal gear was 96 so not sure if it is wired differently than a 94 ? Any help would be greatly appreciated, I'm not sure what my next step should be ? I've been scouring the internet looking for answers but end up dizzy after a few hours thanks Adam
What are you using as a ground reference for the meter?
What was the distributor gear made of on the old distributor? 1994 was the transition from flat tappet cams to roller cams. That necessitated the distributor gear material change. There were no wiring changes, just the gear material.
0.05 volts? 5/100ths of 1 volt? That's a mighty precise meter you have there.
If all of them are wrong then rla2005 is probably on the right track. Ensure your grounds are good (no paint under the washer/bolt, clean the rust off until it's shiny, etc.) You should have 0 ohms from one side of a ground connection to the other.
I've been using the battery as a ground . Should I try going off something else ? My distributor gear was steel , I have a roller cam in the engine but parts guys computers only show iron gears for my year . The harness on the distributor has 6 wires and the truck harness has 5 , not sure if that matters . Also I have a connector at the back of the main harness by the fuel pressure regulator that isn't connected to anything ? I can't see anywhere it would connect, the 2 wires on it are red and yellow with a red stripe and I can't find those on the wiring schematic in my manual . I'll check the grounds out and clean them up . Any other advice? Thanks
I've been using the battery as a ground . Should I try going off something else ?
All of the sensors use a dedicated signal return that goes back to the computer (PCM) on Pin 46. Internally this signal ground is tied to power ground. So in theory measuring from the battery would be okay, but if the signal return wiring is open you will get weird results. You could test that theory by measuring the signal out at the TPS then use the signal return as your ground reference.
Another simple test would be to measure the resistance between Pin 46 Signal Return and the battery negative terminal. It should be a very low resistance. You can pick any sensor's signal return line to represent the input to Pin 46.
An overall diagram of the powertrain control wiring
Originally Posted by Adamazar
My distributor gear was steel , I have a roller cam in the engine but parts guys computers only show iron gears for my year .
Since 1994 was the start of the transition to the roller cam 5.8L engine many parts books are wrong. Using a distributor listed for a 1996 in your truck would be correct.
Originally Posted by Adamazar
The harness on the distributor has 6 wires and the truck harness has 5 , not sure if that matters .
The distributor connector (C178) uses 5 wires:
Originally Posted by Adamazar
Also I have a connector at the back of the main harness by the fuel pressure regulator that isn't connected to anything ? I can't see anywhere it would connect, the 2 wires on it are red and yellow with a red stripe and I can't find those on the wiring schematic in my manual . I'll check the grounds out and clean them up . Any other advice? Thanks
A picture would help. Be sure to inspect and clean ground G101 located next to the battery. That is a very critical ground for the computer.
I have no idea what that connector is supposed to go to. I've look through everything I have and nothing matches those wire colors. Best guess is the wiring harness is common between the 5L and 5.8L equipped trucks so it may be for the knock sensor used on the 5L engines. The 5.8L never used one.
Hey thanks , I was kind of figuring that but wanted to be sure . So I tested the tps last night and the readings were good . I think I may have been doing it wrong before . I've checked the grounds and they appear to be working good . I've been researching , the only thing I really changed was the distributor with a reman one and I've been finding out that a lot of these can come with a bad pip so it's got me wondering if maybe that's causing the problems? I als am wondering if it could be a vacuum leak which I'm hoping isn't the case . Anyone have any good suggestions for checking for that ?
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