4.0 Running Very Rich


Ranger4x4.0

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I've got a 1998 Ranger 4.0. And it is running extremely rich. This might be a little long, but I want to include every detail leading up to this issue that me and my mechanic cannot figure out.

I should mention here and now, through all this, ZERO codes were thrown, and everything checks out to the computer from my understanding. ALSO, the truck has a brand new pcm, few months prior to this, the old one wouldn't read the o2 sensors, and all this may have something to do with the wiring there. But the new computer reads them just fine, and they also check out, so.

September 1st, I got ready to go 1300 miles to Colorado for vacation and was supposed to leave the next day. I got off work, got in the truck, started it up, and it had a little rough idle. I drove it to the gas station, all was fine. I let it idle while I was in the station, and i go back out, and black smoke was pouring out the exhaust, horrid idle and all, I immediately shut it off. I checked everything I could with my eyes, nothing, other than coolant leaking out the side of the block, which it has done for about a year now, never got to it. Vacation canceled! I drove it back to my work, and the next morning, I have a friend come tow it for me to my mechanic. We got there. We start it up, black smoke turning to white over time. HEAD GASKET right!? Idk, but I told my mechanic to change out the head gasket while he's at it, oh, and rebuild the whole darn thing including the transmission! 2 months later, everything is put back together, thousands in new parts, oversize bearings, new pistons, rings, pushrods etc. You get the point. First start, rough, as expected. But it didn't go away. Black smoke pouring out the exasut. When you drive it, it drives and runs like it just came off the lot. When its idling, its pouring gas in the cylinders, fouling out the new plugs.

It has brand new injectors as part of this job. So it can't be the injectors, since it was doing the same thing with the old ones. Something is telling the pcm to run in a rich condition, I really have no clue. What we do know, the ect sensor checks out, the pcm is from my understanding, working properly BUT there is a chance it isn't. My mechanic is dead set on this issue NOT being the pcm, so were going to pass it up for the time being, and figure out what else could possibly cause this. Although, I have talked to a certified ford tech, and he swears up and down, it's the pcm, but my mechanic doesn't think so. I want to say it's the pcm but I also want to trust my mechanic. He was a gm mechanic for decades and a backyard mechanic for another few decades, and he has never once been wrong with any of mine or my families vehicles.

We both don't know exactly what can cause this. I will be going over to help him in the morning to try and figure this out.

So, what should I check? Or replace? Or beat with a hammer?
 


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Ranger4x4.0

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So I got to drive it, and correction, it drives like crap, misfiring probably due to fouled plugs. But no different. Still running very rich. And there's some white smoke mixed with black smoke out the tailpipe.
 

4.0blue98

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It was like that when I found it.
Did the issue happen before or after the "new" PCM? Was it really new or new to you? Were the injectors changed before or after all the rich conditions? New doesn't always mean good. I'm sure the plugs are probably fouled but I can't imaginethe cats like this either.
 

Dirtman

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You don't mention any info on what DTCs it has... if its dumping that much fuel there has to be some codes.
 

Ranger4x4.0

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Issue happened after the new pcm. Months after. And considering I paid $400 for it, I assume it was new. My mechanic bought it though. Again, the rich condition was happening before I had the engine rebuilt and before I put in brand new motorcraft injectors purchased from the dealer. After the engine rebuild and new injectors were put in, no change on the rich condition or the black smoke pouring out the exaust.
 

Ranger4x4.0

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You don't mention any info on what DTCs it has... if its dumping that much fuel there has to be some codes.
I mention it in my second paragraph. ZERO codes thrown between September 1st and now.
 

Ranger4x4.0

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I am worried about the cats though, they can't be good after all this. And yes, I have my suspicion on the issue being the computer. And I told my mechanic this, and he doesn't think so. I don't wanna be mean to the dude and tell him how to do his job, but I've sunk over $3500 in it and it still doesn't run right, I might have to just take it back from him and figure this out on my own, but in the meantime, I need advice on what the issue could be that I should check other than the pcm. If everyone tells me it's the pcm for sure, I'll get another one and see.
 

Dirtman

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Have you checked the fuel pressure regulator? Also it's pretty much impossible for the system to dump that much fuel and the computer not throw a code so something is wrong right there.
 

Uncle Gump

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I would be more worried about my fresh engine rebuild then the cats...

Sure sounds fuel related issues. Not one mention of fuel pressure testing... but I tend to agree... running as bad as you say... should be setting codes.

Another thing I would do... is see what spark plugs were put in it. Nothing but the proper Motorcraft of Autolite plugs if it were mine.
 

Ranger4x4.0

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Have you checked the fuel pressure regulator? Also it's pretty much impossible for the system to dump that much fuel and the computer not throw a code so something is wrong right there.
1998, from my understanding, was the first year for a purge damper thing on the fuel rail instead of a fpr, so it doesn't have an fpr. He did replace the purge damper though, did nothing.
 

Dirtman

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98 could be either style system. Check the fuel pressure, returnless (if functioning) should be 65psi. Older system is 35-45psi. Also only one line from the the tank to the rail on the returnless system, return system has 2 (one is the return obviously). This doesn't include the evap purge line.

I'm more concerned that you have no codes.... I'd wanna look at live data while it's running. Fuel trims, o2 voltages, maf readings etc. Those cannot all be reading right and run that rich. And if they aren't reading right why is the computer not throwing a code. At the very least it should be showing p0172 and p0173
 
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Josh B

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Your mechanic must be one happy fella ;)
 

Ranger4x4.0

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Its returnless for sure. I'm going to take the truck back next week, and take it to another friend's house to store it so I can work on it myself and figure it out. I have no idea why it wouldn't throw a code. It definitely should, but I haven't had the chance to really go through the truck and hook up my computer to it and read any of the data. I'm gonna tell the dude that I'm going to be taking it back, and somehow figure out how I'm going to get it to my friends house, because I definitely ain't driving it.
 

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Can you safely tow it with a rope or tow strap?
 

Ranger4x4.0

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Can you safely tow it with a rope or tow strap?
I talked to my mechanic. He's not going to charge me anything after the rebuild. He said he will fix it for free. I'm going to pick up a new computer. I have the part #, F87z12a650ahb, and my vin. Is that all I need to get the correct computer? I've never first hand bought a computer, and I know there are like 4 different ones just for the 4.0.
 


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