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  #21  
Old August 12th, 2015, 09:26 PM
snow686
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John
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Quote:
Originally Posted by wmatos1001 View Post
Been having a recurring intermittent issue I can't wrap my head around. Thought it might be bad gas but need advice. I have a 1994 NAS Def 90 with stock 3.9L V8.

Issue: on occasion the vehicle suddenly stutters and loses power dramatically but does not actually stall. It can happen at highway speeds and lower speeds. Some times just for a minute or less sometimes a few minutes.

The car runs like it is not getting air out the exhaust almost like someone stuck a banana in the tail pipe. Sounds very muffled and runs on limited power even if floored for a while then goes fine again.

I noticed twice that when it did this and I got a look underneath the cat converters seem very hot (more than normal actually one was glowing red) and I smelled a slight burning smell.

When I shut the engine off, it starts right up and is perfectly fine until it happens again (could be weeks before it happens again).

What I have changed recently (within past 8-10 months) as new parts:
Fuel filter
Fuel pump
Fuel pump relay
Fuel lines
spark plugs, distributor, tune up
Throttle position switch
Cat converters and exhaust
Cleaned out MAF
K&N air filter
Snorkle

What I haven't changed:
O2 sensors

Any thoughts? I don't know what "bad gas" symptoms are like but a few said it could be that.

Any advice would be appreciated!
Thanks,
Will

I had this problem for the past 4 years, and finally figured out what it was last weekend. Go under your passenger seat. take out your ecu. You probably have corrosion there. If so, clean it. I also had some burnt up resistors in my ecu. So i ended up buying a new one that was also chipped and ended up giving me better fuel consumption. from congleton service near burlington, VT. Also, recomend putting insulation between ecu and bottom so when you get water in there it doesn't sit in it.
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  #22  
Old August 12th, 2015, 09:32 PM
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William
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Quote:
Originally Posted by snow686 View Post
I had this problem for the past 4 years, and finally figured out what it was last weekend. Go under your passenger seat. take out your ecu. You probably have corrosion there. If so, clean it. I also had some burnt up resistors in my ecu. So i ended up buying a new one that was also chipped and ended up giving me better fuel consumption. from congleton service near burlington, VT. Also, recomend putting insulation between ecu and bottom so when you get water in there it doesn't sit in it.
The ECU is in the passenger seat box? I only though the jack tool kit was under there? I will look for it and try cleaning it out. Thanks!

------ Follow up post added August 12th, 2015 10:36 PM ------

Quote:
Originally Posted by snow686 View Post
I had this problem for the past 4 years, and finally figured out what it was last weekend. Go under your passenger seat. take out your ecu. You probably have corrosion there. If so, clean it. I also had some burnt up resistors in my ecu. So i ended up buying a new one that was also chipped and ended up giving me better fuel consumption. from congleton service near burlington, VT. Also, recomend putting insulation between ecu and bottom so when you get water in there it doesn't sit in it.
Ah yours is a 1995. On 1994 it is in the passenger footwell behind the card board kick panel where some of the relays are. Not under the seat until 1995. But I will give it a look anyway to see if it is corroded etc.
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  #23  
Old August 12th, 2015, 09:38 PM
snow686
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Quote:
Originally Posted by wmatos1001 View Post
Ah yours is a 1995. On 1994 it is in the passenger footwell behind the card board kick panel where some of the relays are. Not under the seat until 1995. But I will give it a look anyway to see if it is corroded etc.
Sorry about that. AI don't know if yours has black code read out module, but mine did and it was blank, until i fixed the ecu and then it started working again. I have a lot more power now too.
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  #24  
Old August 25th, 2015, 08:19 PM
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Any other thoughts on this being a faulty ECU? The engine cut out/backfired again today twice after working great for over a week without issue. So the problem is very intermittent. Does that sound like ECU? No code is showing, no check engine light at all.

Thanks,
Will
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  #25  
Old August 25th, 2015, 08:41 PM
snow686
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Quote:
Originally Posted by wmatos1001 View Post
Any other thoughts on this being a faulty ECU? The engine cut out/backfired again today twice after working great for over a week without issue. So the problem is very intermittent. Does that sound like ECU? No code is showing, no check engine light at all.

Thanks,
Will
Will,
If it's easy to get to it just look at it. Even an untrained eye can tell if there is corrosion or burnt resistors and transistors.
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  #26  
Old August 25th, 2015, 09:20 PM
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ECU is unlikely to cause intermittent faults in my opinion. Backfires and cutouts are the result of incomplete combustion

1. Change in air fuel fix ... Think excess air - loose plenum tube or hole in air line. Possible IACV issue.

2. Change in air fuel mix - fuel starvation ( or less likely surplus ) .. Check fuel pressure / delivery.

3. Loss of spark ... Cause unburnt fuel to hang around. Think ignition system.

The ECU runs only with a signal form the coil. No signal = no fuel.

I would put an oscilloscope on the ignition system to see what's going on ... Mine cost $150 off craigslist and isn't hard to use.
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  #27  
Old August 25th, 2015, 09:22 PM
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The ECU controls all those things.
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  #28  
Old August 25th, 2015, 09:23 PM
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Quote:
Originally Posted by snow686 View Post
Will, If it's easy to get to it just look at it. Even an untrained eye can tell if there is corrosion or burnt resistors and transistors.
If there are burnt resistors and transistors the ECU would be toast and it wouldn't run. This is something that happens and doesn't. Sounds like something loose ..
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  #29  
Old August 25th, 2015, 11:37 PM
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Chris Davis
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Maybe check out the TPS. Check the resistance and see if it is a smooth transition when rotating knob. Could be fuel pump on way out as well.
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  #30  
Old August 26th, 2015, 04:31 AM
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Bill Adams
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Quote:
Originally Posted by snow686 View Post
The ECU controls all those things.
No, it doesn't. The ECU controls only how long the injectors are open per event.
Stumbling and loss of power are usually one of two things. Fuel mix wrong or spark
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  #31  
Old August 26th, 2015, 06:45 AM
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Kevin Keith
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I've had two similar situations:
1 - wires to the ignition amp got a bit toasty from the exhaust manifold & would short out randomly.
2 - hose from the MAF to the intake had failed inside & a again randomly would collapse starving the engine of air.

Just a couple of thoughts & easy checks.
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  #32  
Old September 5th, 2015, 06:50 PM
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Update: I changed out both O2 sensors first and drove it for a few days and the issue kept occurring.

I then changed out the ignition coil with an OEM Bosch unit I picked up on Amazon (new in box) for $50. I have been driving it and so far so good, no issues, no cut out, no backfire/lean mix.

I also noticed another benefit. The car definitely has more power. Past 3,000 rpm my Defender would not really get any power, especially in 5th gear. Now it pulls strong with noticeable power past 3,000 rpm and when on the highway I get meaningful (not sports car) acceleration that I did not have before.

Is it possible that the existing coil was weak/bad and aside from intermitted cut out or lean running it was retarding the engine combustion through weaker spark?

I'm not fantasizing about the power increase. My wife even called it out on our first test run. She said it right away before I did.

Interested in thoughts on this.
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  #33  
Old September 6th, 2015, 08:02 AM
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Quote:
Originally Posted by wmatos1001 View Post
Update: I changed out both O2 sensors first and drove it for a few days and the issue kept occurring. I then changed out the ignition coil with an OEM Bosch unit I picked up on Amazon (new in box) for $50. I have been driving it and so far so good, no issues, no cut out, no backfire/lean mix. I also noticed another benefit. The car definitely has more power. Past 3,000 rpm my Defender would not really get any power, especially in 5th gear. Now it pulls strong with noticeable power past 3,000 rpm and when on the highway I get meaningful (not sports car) acceleration that I did not have before. Is it possible that the existing coil was weak/bad and aside from intermitted cut out or lean running it was retarding the engine combustion through weaker spark? I'm not fantasizing about the power increase. My wife even called it out on our first test run. She said it right away before I did. Interested in thoughts on this.
It's also possible the leads to the old coil were slightly corroded and just swapping the coil cleaned it up. The way to tell is swap the old coil back in and see if the old problem returns.

The only way to know root cause is to be able to replicate the problem at will.
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Soapy water / KY jelly, etc. is is basically a must. Yes, good idea to remove trim panels - only takes 5 more minutes to do so.
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  #34  
Old September 7th, 2015, 06:11 PM
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I had ignition issues a few years ago and it ended up being the ignition control module. After I discovered the smoking gun, I put dielectric grease on all terminals and secured all wiring.
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  #35  
Old September 7th, 2015, 09:43 PM
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Quote:
Originally Posted by Grover View Post
I had ignition issues a few years ago and it ended up being the ignition control module. After I discovered the smoking gun, I put dielectric grease on all terminals and secured all wiring.
I have a new in box Lucas ignition control module/amplifier that was going to be next swap out if the temporary cut out kept occurring after replacing the coil. So far the lean/cut out hasn't happened again so may have been the coil.

But of course after just fixing the coil the next day my water pump started leaking and some water/coolant is pooling on the top where it meets the block. So now I'm on to that. Might just be the pump gasket but if I need to replace that I will likely just get a new OEM water pump in while I'm at it. These are the items that look to be all original that will likely start to fail so prefer to get new parts rather than wait for it to go and be stranded.

Never ends!
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  #36  
Old September 8th, 2015, 06:29 AM
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Quote:
Originally Posted by wmatos1001 View Post
I have a new in box Lucas ignition control module/amplifier that was going to be next swap out if the temporary cut out kept occurring after replacing the coil. So far the lean/cut out hasn't happened again so may have been the coil.

But of course after just fixing the coil the next day my water pump started leaking and some water/coolant is pooling on the top where it meets the block. So now I'm on to that. Might just be the pump gasket but if I need to replace that I will likely just get a new OEM water pump in while I'm at it. These are the items that look to be all original that will likely start to fail so prefer to get new parts rather than wait for it to go and be stranded.

Never ends!
There are 2 small front heater hoses. The hose clamp of one can rub the other and create a small leak. Try using a pressure tester on the system and you'll see water emerge from any holes under pressure.
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Soapy water / KY jelly, etc. is is basically a must. Yes, good idea to remove trim panels - only takes 5 more minutes to do so.
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  #37  
Old September 8th, 2015, 06:57 AM
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Loic Fabro
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I agree with leastonce's idea. My experience with water pumps dying were all about the bearing dying/leaking (3 or 4 so far on two different trucks). The top hose(s) failed on my truck too and puddled on the top of the engine.
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  #38  
Old September 8th, 2015, 06:32 PM
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Quote:
Originally Posted by MonLand View Post
I agree with leastonce's idea. My experience with water pumps dying were all about the bearing dying/leaking (3 or 4 so far on two different trucks). The top hose(s) failed on my truck too and puddled on the top of the engine.
Thank you both (cc leastonce) I'm familiar with the two hoses you are referring to and recall them being really snug / close. When I have a chance tomorrow I will take a look at them to see if there is an issue there.

Makes perfect sense that pooling on the top flat section of the water pump would be due to the two hoses above it, not the pump itself.
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  #39  
Old June 19th, 2016, 07:22 PM
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UPDATE: I think I have finally fixed the issue in my original post. I purchased a 14CUX that I believe came off of a 1994 RR. I simply swapped in the replacement 14CUX, turned the car on and noticed right away it idled perfectly solid at 1 or 2 notches below 1,000 rpm. Prior to the change my car would always idle at 1,000 or just over and usually much higher when cold.

After the power loss and raw fuel dumped into my cats again one time earlier today and three times yesterday I test drove it numerous times today and it was perfect after the replacement 14CUX went in. I also noticed after driving and coming to a stop this drops quickly to a good idle unlike before when it would surge and then very slowly drop to a slightly high idle at a stop.

I drove it again tonight and it has not driven this smooth since I purchased the vehicle 2 years ago. It is running great and not as jerky at very slow speeds as before.

I am keeping the old 14CUX to swap back to replicate the problem to confirm I have it licked in the next few days.

Fingers crossed but I have a feeling this is it!

P.S. I found out the place I purchased the 14CUX from had another just like it so I bought that one as a spare.
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  #40  
Old July 13th, 2016, 08:25 AM
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Drew Rogers
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Where did you find the 14cux? I am looking for one.
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