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'93 LWB with a history of dizzy/IAM issues. After dis-connecting every part of the remote IAM on the Left fender, cleaning all the corrosion at every point of contact (I thought that was the problem; lots of corrosion where the IAM mounting plate mounts to the fender, and where the engine ground strap and condenser bolt down), removing the IAM itself and cleaning/re-applying dielectric grease to it's contact surface, the probem still persists (tach came back to life, though.....).

It fired up and ran like a top for the first 10 min, then began tomis-fire again at ALL engine and road speeds.

Seems to be occurring when it’s hot, or after a few minutesof running, although during the rough running, it HAS momentarily changed backto running well. Example: After starting it and running beautifully down thehighway for ~6 mi, I pulled off and took a leisurely road @ 40-50 mph, stoppedto look at a used car and left it idling. After idling for ~ 2 min, it began tostumble. Got back in quick and turned around for home, rough-running until Igot to a stop light, where it mysteriously idled fine. Acceleration on thehiway on-ramp was clean, then stumbling again @ 65 mph. Seems to run well onacceleration, but the symptoms are definitely random.

During the rough-running, I can smell un-burned fuel, whichconvinces me this is (again) an ignition problem.

I will probably look at the plugs, but they’re no more than20k old, and the symptoms don’t point to plugs. Wires and coil are new, condenser is OLD and corroded. Could that be it?

How do I test the IAM itself? Do they often go bad?
 

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your condenser is a noise supressor, how are your ignition wires? how old is your coil? how are your oxygen sensors? att of this comes into play with rough idle, have you checked for vacuum leaks?.
 

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Discussion Starter #3
Wires and coil are new (~3k miles old). Wouldn't o2 sensors trip a fault code? Vacuum leak may be valid, but this is NOT an idle issue, it happens at high speed also, and when it's not "happening", idle is smooth. Vacuum leaks don't behave like that, but then again, I'm out of ideas.
 

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If it runs fine sometimes but not others I would look at wiring connections. I had a road trip once where we ended up having to pull over and stay the night in the hotel because the car was acting up.
I tried all sorts of things to fix it when it ended up being a loose connection on the coil. It threw a CEL code 48 (stepper motor) for some reason. I would check your connections to the coil.
Coil positive should have:
- Mag pickup positive
- 12v Ignition Wire

Coil negative should have:
- Mag pickup negative
- Fuel injection wire

Sometimes the 12v positive is soldered into the Mag pickup positive and that connection can get dodgy.

Also, I believe dielectric grease is an insulator. It makes connections less conductive, not more. It shouldn't be used on contact surfaces.
 

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Forgive me, what is this "MAG" you're referring to?

Sorry, the Mag is the magnetic pickup which comes from the side of the distributor and connects through a bundle of wires to the coil. There is a positive and a negative wire. Positive is white, and negative is white/black I believe. If those signal wires aren't making a good connection from the distributor to the coil, then the coil wont fire right and may causing missing and stumbling. Its worth tracing them and making sure all those connections are clean and the plug into the magnetic pickup on the distributor is on firmly.
 

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Wires and coil are new (~3k miles old). Wouldn't o2 sensors trip a fault code? Vacuum leak may be valid, but this is NOT an idle issue, it happens at high speed also, and when it's not "happening", idle is smooth. Vacuum leaks don't behave like that, but then again, I'm out of ideas.
check out britishv8,com/14cux it explains in great detail the contribution of every component in regards to engine performance,
02 sensors play a very vital role specially on nas vehicles.
 

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I assume you have had the stepper motor out and cleaned it up?

Don't discount vacuum issues. I have just had to replace the brake servo due to a split diaphragm which was causing a loss of power on a random basis with a smell of petrol. The ECU was throwing petrol in by the bucket load!
 

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Discussion Starter #12
PROBLEM SOLVED! It was the trigger-wheel inside the dizzymaking hard contact with the mag pickup as it spun around. Replaced parts, setair gap, purrs like a kitten now!
Thanks all, I KNEW it wasn’t a vaccine leak!
 

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Discussion Starter #14
PROBLEM NOT SOLVED!

After fixing the dizzy, it ran perfectly for 2 days, then itbegan doing it again, it a less “intense” manner, but stillstumbling/misfiring.
Starts up and purrs just fine, then 6-7 miles down the roadit will miss at highway speed, then down to a stop sign it’s stumbling andidling really low. It will pick up if you hit the gas to accelerate, but itwill still miss throughout the rpm range, which tells me it’s NOT the steppermotor (which was replaced less than 2k miles ago).
Seems like a heat-related thing, because it doesn’t act thatway when cold. I CAN clean the stepper motor AGAIN, but back to one of myoriginal questions:
Is the ignition amplifier test-able? I think I should justswap in a new one and try that.
 

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PROBLEM NOT SOLVED!

After fixing the dizzy, it ran perfectly for 2 days, then itbegan doing it again, it a less “intense” manner, but stillstumbling/misfiring.
Starts up and purrs just fine, then 6-7 miles down the roadit will miss at highway speed, then down to a stop sign it’s stumbling andidling really low. It will pick up if you hit the gas to accelerate, but itwill still miss throughout the rpm range, which tells me it’s NOT the steppermotor (which was replaced less than 2k miles ago).
Seems like a heat-related thing, because it doesn’t act thatway when cold. I CAN clean the stepper motor AGAIN, but back to one of myoriginal questions:
Is the ignition amplifier test-able? I think I should justswap in a new one and try that.
I'm putting my bets on the amplifier.

80% of warmup related misses trace back to that.
 

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Take the amplifier off and check the resistance across the two tabs. should be between 3K and 5K I believe but a totally knackered amp would result in a no start. Not sure if they do get affected by heat.
 

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did I miss where the pick up has been tested? also you mentioned having used dielectric grease as an insulator on the amplifier. this does not disperse heat or insulate from arching, you need to find and use heat sink paste for positive and long term results.
 

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PROBLEM NOT SOLVED!

After fixing the dizzy, it ran perfectly for 2 days, then itbegan doing it again, it a less “intense” manner, but stillstumbling/misfiring.
Starts up and purrs just fine, then 6-7 miles down the roadit will miss at highway speed, then down to a stop sign it’s stumbling andidling really low. It will pick up if you hit the gas to accelerate, but itwill still miss throughout the rpm range, which tells me it’s NOT the steppermotor (which was replaced less than 2k miles ago).
Seems like a heat-related thing, because it doesn’t act thatway when cold. I CAN clean the stepper motor AGAIN, but back to one of myoriginal questions:
Is the ignition amplifier test-able? I think I should justswap in a new one and try that.
Whereabouts are you based? These amps are not expensive and know failure items. Best to replace. Simonbbc is a good sources for V8 ignition parts and sells the amps, brackets and cables.
 

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Discussion Starter #19
also you mentioned having used dielectric grease as an insulator on the amplifier. this does not disperse heat or insulate from arching, you need to find and use heat sink paste for positive and long term results.
AHA! I DID use dielectric grease, not knowing what came with there-location kit. I even thought about it, then rationalized that the dielectricgrease is not an electric conductor, but may be a thermal conductor, so Ilet it go. Am I wrong in that regard?

Regardless, I will find some heat-sink paste and re-install.
I also installed the used amplifier that came on my donordizzy. It is of unknown condition, but the truck ran exactly the same. I willpull it and test both to see if they fall where Range123 says they should.
But what are the chances that BOTH amplifiers are faulty inthe SAME manner? I guess if they both were to fail they’d fail at about thesame time/temp. But I found one on Amazon for under $30, so I’ll buy that,measure it first just to see, then install it with heat-sink paste.
Whew, even if none of this works I feel better that dudeslike you will throw out rational suggestions to give me hope! I promised my17-yr-old he’d be able to drive this truck proudly to school and hockey, and sofar he’s stuck with the Hyundai his aunt gave him (and my F150, but I getnervous when he drives that).
Thanks everyone, I will report back!
 

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AHA! I DID use dielectric grease, not knowing what came with there-location kit. I even thought about it, then rationalized that the dielectricgrease is not an electric conductor, but may be a thermal conductor, so Ilet it go. Am I wrong in that regard?

Regardless, I will find some heat-sink paste and re-install.
I also installed the used amplifier that came on my donordizzy. It is of unknown condition, but the truck ran exactly the same. I willpull it and test both to see if they fall where Range123 says they should.
But what are the chances that BOTH amplifiers are faulty inthe SAME manner? I guess if they both were to fail they’d fail at about thesame time/temp. But I found one on Amazon for under $30, so I’ll buy that,measure it first just to see, then install it with heat-sink paste.
Whew, even if none of this works I feel better that dudeslike you will throw out rational suggestions to give me hope! I promised my17-yr-old he’d be able to drive this truck proudly to school and hockey, and sofar he’s stuck with the Hyundai his aunt gave him (and my F150, but I getnervous when he drives that).
Thanks everyone, I will report back!
When building PCs, we used to use Arctic Silver 5. It's long been obsolete as a thermal paste, but is a very weak electric conductor because it has some silver in it (as opposed to most modern pastes which aren't conductive period).
 
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