1988 RRC running really rough - Defender Source
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  #1  
Old February 10th, 2010, 10:47 AM
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Chris Davis
94 NAS D90 6.2LS
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1988 RRC running really rough

But it starts and idles but when I give it gas, it seems like it misses, won't high rev and runs really rough. I just dropped my 3.9 I had taken out of my D90 (which worked fine) and used it (as a small block) to replace my older 3.5. The 3.5 had similar problems, so I know it is a sensor or component I have swapped. The EFI light is on which is triggered by most likely one of the following: Temperature sender, MAF, Stepper Motor, O2 sensors, or possibly the fuel pressure regulator. I don't think it is the stepper since I swapped a known good one in. Probably not the O2 sensors since they only really come into play when the engine is warm and the problem is both warm and cool, but I have not ruled them out. I am planning to swap out the temp sender and O2 sensors from my D90, but I wanted to see if the symptoms seemed familiar to anyone since I do all this in my driveway, it is 4F outside, and there is snow on the trucks. Any help on diagnosing it would be great. Thanks!
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  #2  
Old February 10th, 2010, 11:15 AM
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S. Smith
72 Series III 109 Diesel
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Did you swap the ECU's? I would make sure you have the right one for the motor that is in now in your RRC. Also check your ground wires, wierd stuff can happen if you missed one on the install.
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  #3  
Old February 10th, 2010, 11:20 AM
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Chris Davis
94 NAS D90 6.2LS
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I have checked the ground wires carefully as that had plagued me in the past and is great advice. I have not swapped the ECU since the 13CU is not the most common of components--If the other things don't pan out, I will search for someone with another '88 and see what I can find.

It sort of feels like it is also in "limp home mode"--would any (which one?) of the failed components force this condition?
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  #4  
Old February 10th, 2010, 11:21 AM
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S. Smith
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You might need the 15 CUX, worth the 5 minutes to swap to see.
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  #5  
Old February 10th, 2010, 11:46 AM
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Lucas Forgue
2011 Rangie
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either ecu 13 or 14 should allow the truck to run fine ive tried both on my truck when i had a stalling problem and didnt notice any change in running..........id try swapping the coolant temp and fuel temp from your 3.9 and see if thats any better..........

have you checked fuel pressure or volume?

i also had a bad fuel filter that would cause some strange shit too

let us know how you make out
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  #6  
Old February 10th, 2010, 12:19 PM
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Dendy Jarrett
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Three things come to mind if the truck is running but is running rough or has difficulty idling evenly:

1) Stepper- Little valve in passenger side of back of the top of the motor. two wires connected to it. Clean with q-tip and alcohol, or replace. Mine was filthy and cleaning it did the trick. Removed the wire connectors, backed it out, cleaned, and reinstalled. No mechanic skills really necessary.

2) Your base idle is out. This usually needs to be re-set by the dealership. It will cause the truck to run, but constantly die out or have no idle at all.

3) Mass Air Flow (MAF) has gone bad or needs cleaning. This is the inline air flow sensor that tells the truck how much air the motor is getting and that it is enough of the correct mix. Mine went bad, and a replacement made all the difference. I now keep a spare in my on-board tool box.


Oh, and one more thing. Many times the ECU on a Classic just plain hic-cups. You may have a light on the dash suddenly appear. Mine was idling like heck one time and the engine light came on. I simply disconnected the battery for a minute, and then reconnected it. Cleared the mess right up. Makes me laugh, as sometimes these things are like old TV sets ... and just need a good slap on the side!
Hope that helps.

Dendy
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  #7  
Old February 10th, 2010, 11:55 PM
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Chris Davis
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I swapped ECU's, checked distributor air gap, fuel pressure regulator vacuum and distributor cap/rotor and none of the above are the issue. Trucks starts first try, idles fine, revs ok but does miss, but when you try and drive it, once there is load on the engine, it runs like crap and won't go much at all. I'll try and swap the pressure regulator, coil and try and find a MAF to swap this weekend... search continues.
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Old February 11th, 2010, 12:00 AM
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Clogged cats?

Bad TPS?

I would just swap or unplug sensors until it runs right and you have your culprit (benefits of owning multiple rovers).
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  #9  
Old February 11th, 2010, 10:36 AM
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Jon
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I had a O2 sensor unplugged one time and caused it to run on only 4 cylinders. Plugged it back in and bingo right back to normal. Might be worth a try. You could also just take your D90 O2 sensors and plug them in out in the air for a quick test.
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  #10  
Old February 11th, 2010, 11:30 AM
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Chris Davis
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Yeah, it is going to be a plug and play weekend. The D90 shares the same O2, fuel pressure regulator, temp sender, AIC valve and MAF, so that is the game plan this weekend. I have already swapped ECU, coil cap/rotor and some other stuff, so I am on the fast track of ruling stuff out. I'll check to see if the cats are getting wicked hot--only way I know to check if they are clogged. I have checked the TPS with an ohm meter and seemed smooth, but will check it with a volt meter this weekend. Thanks as always--love knowing if I have missed something since obviously I have...
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  #11  
Old February 14th, 2010, 01:17 AM
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Chris Davis
94 NAS D90 6.2LS
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First and foremost, the truck is running AWESOME! A few things were wrong simultaneously, which compounded diagnosis, so I wanted to sum them up with how I would go about diagnosis in the future. After I put in the motor which I knew to be good as I pulled it from my D90, the truck would not start. What went wrong: fuel pump, Injectors, distributor.

Nothing improved more than when I replaced the fuel pump, as the old one was dead. The quickest way I know of to check the pump is jump it on at the fuel relay--if it does not come on, check the connection at the tank and see if it has voltage. Quick and easy. Mine was dead, changed it and the truck started, ran rough.


First step--pull your plugs, at least a couple if not all. They tell a great story--learn how to read them. Get a plug cleaner from Harbor Freight or where ever--one of the pneumatic types (on sale right now for $19, get extra abrasive for $4). Sooty or gassy plugs might not start. A fouled plug may mask even a potential fix if it doesn't fire. Now the truck ran, but crappy to say the least, sooty plugs/o2 sensors.

Next step: Use the manual's diagnosis check list utilizing the CPU and it's cable connector by taking voltage and resistance readings. It takes very little time (relatively), and diagnoses the components that it relies on to make decisions--namely it's sensors. I swapped a lot of components which proved a waste of time. It may not mean something is not failing, but it will say look for something else, first. It only found one thing for me--my injector bank resistance was 5.7 ohms which means that 1 of the injectors on that bank was wrong which my plugs confirmed. I had a spare set and when I changed them out, I noticed things improved but I still had a huge power issue under load.

It sure felt like a mechanical advance failure on the distributor as it happened at higher rpms when the otherwise nice running truck went to hell if it was under load and I had truly ruled out all other potentials. I opened up the distributor and noticed that the pickup rotor was rotating a bit. It turns out there is a plastic "keyed" spacer between the pickup rotor and the shaft and it had broken. I replaced it and BAM, last thing solved, truck is a champ.

I am happy I originally took the long road and examined each and every sensor and learned how to individually diagnosis them. It is a colossal waste of time as a procedure (muck quicker at the ECU) but vital for the future "intuitive" logic feature and to know what is truly what (including potential bypasses if you are in BFE).
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