Check Engine light, multiple codes...argh - Ranger-Forums - The Ultimate Ford Ranger Resource


4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

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Old 08-13-2007
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Check Engine light, multiple codes...argh

Guys,

Really need some help with my '94 4.0 Ranger. I've had it for a little over two years now with zero problems and now I've got one I can't seem to figure out.

First off, as back-story, I had my clutch replaced last month by a local shop. When I picked her up the check light came on, so I took the truck back and had them scan it. They said I needed a new O2 sensor and it'd be $120. I knew I could do this cheaper myself and I did.

I replaced BOTH O2 sensors for less than they wanted for one (part only).

Anyway, after replacing them (and clearing the code) the check engine light came back on. The codes I have are:

172
173
176
177

Lean and Rich on both sides. How? What else should I be looking at? I removed and cleaned the MAF and also searched for a vacuum leak (which I didn't find).

Help!

-Matt
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Old 08-13-2007
04 EDGE
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sounds like you have a vacuum leak, matt how close are you to westland?
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Old 08-13-2007
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Very close. Dearborn.

Other symptoms are that it doesn't feel like I have full power. I'd guess, from the seat of the pants, 70-80%. Also, when I'm in 4th or 5th gear and cruising for a few minutes it'll catch, or start to speed up, ie give me the power back for a bit. It's a weird situation that I really need to track down.

Any help is greatly appreciated.
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Old 08-13-2007
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A fuel pressure regulator on the blink might cause concurrent lean and rich codes.

If your '94 4.0L uses a camshaft position sensor (for SEFI), then that might be somethig to look at, as well.
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Old 08-14-2007
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Crawl underneath and trace the wires from the O2 sensors back up into the engine bay.Sounds like they may have pinched the wires between the block and bellhousing.
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Old 08-14-2007
04 EDGE
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sounds like the classic 4.0 OHV upper intake gasket leak!
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Old 08-14-2007
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Quote:
Originally Posted by 04 EDGE
sounds like the classic 4.0 OHV upper intake gasket leak!
Or a lower intake gasket leak...
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Old 08-14-2007
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I replaced the driver's side valve cover gasket a year or so ago, but could replace those two. I just hate to keep trying different parts...but it sounds like this could be the possible cause? Should I just go ahead and replace both intake gaskets?
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Old 08-14-2007
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I'd have a used oil analysis done. Inexpensive and easy to do. It can tell you some important things.

See: https://www.ranger-forums.com/forum2...ad.php?t=44937
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Old 08-14-2007
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I vote for a vacuum leak or the IAC is stuck open to some degree.

Rich
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Old 08-14-2007
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Quote:
Originally Posted by OTRtech
Crawl underneath and trace the wires from the O2 sensors back up into the engine bay.Sounds like they may have pinched the wires between the block and bellhousing.
Good point. I've heard of this happening to several people who have replaced trannies on different vehicles. I particularly recall reading about a single sensor (forgot which one) which had its harness connector pinched like you describe during a tranny swap. It affected the vRef signal (~5v) wire which is an important circuit shared by several other engine control sensors. Bottom line, the car would not start after the swap. It took a lot of time, labor and head-scratching before the problem was finally found and repaired.

Last edited by Rockledge; 08-14-2007 at 10:18 AM.
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Old 08-14-2007
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I thought about that, but I replaced the O2's after the clutch was replaced. The wires are fine.
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Old 08-14-2007
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have you checked the PCV hose..?

btw, welcome to the forums!
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Old 08-14-2007
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Thanks for the help, everyone. I really do appreciate it.

I'll probably replace the PCV, just because it's cheap and I'm not sure when (or if) it's ever been done...but I just don't buy that this isn't related to the clutch work I had done. The truck was running perfectly when it went in and the minute I drove it away, this began. The response I got from the shop was, "Well, it's the O2 sensor because it's 14 years old, blah, blah." Well, after replacing both of them the issue is still here. Thus, my reluctance to take it back for troubleshooting/repair.

04 EDGE, if you have any spare time in the next week or two, let me know as I wouldn't mind an extra set of eyes on it.
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Old 08-14-2007
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the wrong O2 in the wrong bank can cause this.. soi make sure the o2s are plugged into the rigth connector .. also the pinched wire is a good idea although i would think yoiu would get an 02 code.an exhaust leak can also cause miss information from the 02 sensors due to the extra air that can get in due to a leak..

but what i sugest is not just replacing everything, believe it or not 90% of problems can actually be diagnosed and although may take more time to start it will save you agrevatipon and money in the long run..

with that said you said its a 94, i hope it is OBDII if it is get your self a code/data reader. it can help you out imensly now and in the future with any OBDII car you have or will have, so its a good investment. once you get that check the fuel trim and votages from the 02 sensors, this way you can physically find out if its lean or ritch. also one last note check between the rear of the enigne and the fire wall, carlessly droping the engine down when doing a transmission can cause the back of the engine to hit the fire wall and break random stuff back there!

good luck, JOSH
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Old 08-14-2007
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Not OBDII, unfortunately. Thanks for you advice, though! I've spent a lot of time looking at this thing, but I do agree it isn't wise to just start throwing parts at it.
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Old 08-14-2007
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Quote:
Originally Posted by TippsTheFoo
The truck was running perfectly when it went in and the minute I drove it away, this began. The response I got from the shop was, "Well, it's the O2 sensor because it's 14 years old, blah, blah." Well, after replacing both of them the issue is still here. Thus, my reluctance to take it back for troubleshooting/repair.
heh heres something funny, when me and my dad (04 EDGE) did my clutch we managed to break my rear o2 sensor.
the long part that the wires come out of broke away from the part that bolts in and you could move it around.

i would check out the elbow at the pcv, or the entire hose, im not sure how your truck is setup.
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