I been having a few issues with my 1994 F-250, 5.8l, E4OD plow truck. The truck has 80,000 hard miles. I'm not sure if these issues are related or completely separate. So here goes:

Over the last few years I have gotten codes 334 and 337 and had on and off drive-ability issues. I started by replacing the EVP with a new Motorcraft unit. Issues went away but came back. So I took it in to a mechanic and was told the EVP was bad. He replaced it. Issue went away and came back. Mechanic said EGR was bad. He replaced it. It was better but would still set codes occasionally. It seldom did it in cold weather when plowing so I put up with it.

I had to have the transmission recased last fall because the case had two broken mounting ears and had cracked 3 flex plates. A couple of months later I noticed a hard shift from 1st to 2nd and a hard shift into reverse. I assumed this meant it was in limp mode. I had to wait until recently to start checking things out. I Recently checked codes and now have 172, 334, 337, and 624. The brake down is as follows :
KOEO = only has code 624
Continuous memory = 334, 337, 624
KOER = 172, 334

To add insult to injury my battery light came on when I went to up grade the cables to the plow and is staying on even though I disconnected the plow cables and have tried two different good alternators. Right after this happen it started killing occasionally when warmed up and put in reverse. Never did that before.

I found the oxygen sensor to be the original and the wires were pulling out of the top. I replaced it and I still get code 172. I think I had this code a couple of years ago but it had gone away so I did not follow through at that time.

I don't think 334 and 337 are related to the 624 code since I had the 334 and 337 long before the 624.

I pulled the plug to the solenoid pack and found it wet with transmission fluid. I cleaned it out and dried it but still get code 624.

I seem to have a bunch of issues. Anyone had similar problems that were related? Any thoughts?

Thanks.

 

for the hard shifting issue... i'd check your MLPS on the side of your transmission. there's a connector on it that's notorious for taking on moisture and causing hard erratic shifts. if this is the case... there is an upgraded harness you can get that has water tight connections.

for the EGR/EVP issue... first, you can check your egr by hooking a vacuum hose to your egr while the truck is running. if it immediately dies; the mechanical part of the EGR valve is working. for the egr sensor on top, you can remove it and hook your ohm meter to the pins and watch the resistance change as you depress the pintle on the sensor. if they change.. the sensor is good. if both of those test good, work your way back from the EGR valve vacuum line to the two black vacuum solenoids checking for breaks in the vacuum lines. if they're the red, white, green plastic ones... you might as well replace them because there are many reports of them dry rotting and causing leaks that are very hard to detect. once you have that checked, measure the resistance of the coil of the vacuum solenoids i mentioned earlier. make sure they read roughly the same resistance. also check the read the coil resistance to ground... you should have nothing. these will go bad and blow a fuse sometimes. if you find a shorted one, check your fuses.

for the O2 sensor... i never recommend ever replacing parts without troubleshooting first, but the O2 sensor is probably the most important sensor in your vehicle for keeping it running as efficiently as possible and they become less accurate with age... if money is no concern, it may be worth replacing it if it's not somewhat new. if not, you can measure the voltage with the O2 sensor unplugged and as warm as possible. You should see it modulating it's voltage (not staying the same) to indicate lean/rich/lean/rich. if its stuck at one voltage... it's not functioning properly or isn't warmed up. *side note* the O2 sensor creates it's own voltage. you can read 12v at the harness going TO the sensor but this is only to the heating coil inside of the O2 sensor. the signal actually originates at the O2 sensor (neat).


the egr and lean issue MIGHT be connected... i doubt the shifting issue is related...

 

Thanks for the tips. So far I did the following.

1) Checked the MLPS connector. It was dry but dirty so I cleaned it and reconnected. Also rechecked the plug to the coil pack to see if fluid had leaked back in. It was still dry.

I thought I was on to something when I saw that the drive shaft had worn out the harness that goes to the transmission. It was previously taped up. I took the tape off but did not find any damage to the wires so I put fresh tape on it and wire tied it out of the way.

2) Checked the EGR. It holds vacuum and effects the idle if applied while running. Also checked the EGR sensor the resistance changes as vacuum is applied. Checked the green line by applying vacuum to one end and plugging the other. The needle dropped very very slowly so there may be a slight leak or I may not have had a good connection. I needed three hands to do that. I did not get to checking the solenoid. But which fuse can blow?

3) I had recently replaced the O2 sensor because the wires were pulling out of the top and the sensor was coming apart. Didn't get a chance to check for voltage.

Now it get's frustrating. I let it warm up to the point the thermostat opened and never got the check engine light to come on. Took it for a drive until the temp gauge made to the middle (the highest it gets). It still has the hard 1st to 2nd shift, which does not set the CEL anyway but the CEL never came back on for the other issues. Of course the battery light is also still on but I expected that as I did not work on that this time.

I did notice that a patch I had done on the air injection pipe was leaking again. The right side nut that holds the pipe to the exhaust manifold had rotted off. There was a slight gap between the pipe and the fitting on the manifold. I had wrapped an exhaust bandage around it and put on two hose clamps. It lasted the winter. I have a replacement tube with nut but don't know if I can get in there to replace it so have put that off. Can a leak at that pipe cause any of these issues? It sound like it pushes exhaust out rather than suck anything in.

Thanks again for the help. I'll try to check some more stuff later because I know that light will be back on.

 

[QUOTE=musicars;15678451]I'll try to check some more stuff later because I know that light will be back on.[/QUOTE



you can still get codes even if the CEL is not illuminated. Only certain ones turn on the CEL and after a certain number of miles. IIRC the solenoids have 12v to them constantly and are actuated by switching the ground. So, if you have 12v at them, your fuse isn't blown. You should be able to kill the engine with the vacuum on the EGR valve.