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Discussion Starter #1
Today we took Daisy (the 1987 RRC I have been struggling with) on the first extended drive post install of the 14CUX (and other special guests) to eliminate a nagging issue with cutting out. Results were mixed. We drove about 150 miles, both extended highway speeds and in town stop and go. Shortly after the trip started, we experienced one brief cutout, or hiccup, and the EFI light came on. Through the rest of the day, we had several other hiccups, nearly all at the exact point where I would ever so slightly lift off of the throttle. The length of the hiccup varied from an immeasurable blip to nearly a second.
When we got home, I hooked up RG and scanned her. Found a TPS code. I checked the at rest setting and got 3% absolute. I ran the gas pedal in and out and got reasonable smooth response across the range, taking into account some response lag in RG readings. I had set it at rest via a DVM at recommended settings. Anyone have any info on what RG says their at rest readings are?
The fact that the hiccup happens in direct relation to accel pedal movement makes me suspect my "new" TPS could be wonly, but could the setting be causing this behavior as well?
Otherwise, no issues. Good power, still has a high idle at startup that settles down quickly and no glitches in acceleration throughout the movement of the ccel pedal (other than the occasional hiccup, which always seems to coincide with letting off the pedal, not pressing down on it.
 

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Today we took Daisy (the 1987 RRC I have been struggling with) on the first extended drive post install of the 14CUX (and other special guests) to eliminate a nagging issue with cutting out. Results were mixed. .
It's a dying TPS plain and simple, don't make it hard on yourself. Clean it and the small chamber, otherwise try and get a cheap replacement.

Worst case go Tornado since it's cheaper than the NOS part.
 

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Discussion Starter #3
Just ran pinout test on TPS, and as you guessed, it's got dead spots.
This is a newer, replacement Lucas unit. I think it has been bad from the start....

It's a dying TPS plain and simple, don't make it hard on yourself. Clean it and the small chamber, otherwise try and get a cheap replacement.

Worst case go Tornado since it's cheaper than the NOS part.
 

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That’s why I went with the one that I posted.

It includes adapter and comes with and allows you to use cheaper and more available Colvern TPS units in the future.
 

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Discussion Starter #7
OK, got one coming, but interesting and troublesome side note:
I disconnected the TPS and drove around just to see what happened. The rig actually ran very well, started normal, ran and accelerated fine, no rich smell in exhaust, until..
The dreaded 1500 RPM cut out returned! I pulled over, cleared the code, plugged the TPS back in and started it, all is fine, no more 1500 RPM cut out....?? Now obviously this did not heal a wonky TPS, and I expect the hiccup to continue/come back, but what's going on?
Now I had tried to reset the EFI light and succeeded when I had the 13CUX ECU in place, but it would not resolve the 1500 RPM cutout issue. Putting the 14CUX ECU in is what fixed that, or was it..
I wonder what took place within the 14CUX, while not getting a TPS signal, to go into the 1500 RPM cut out mode?
Is it possible for these ECU's to retain a hard set fault or limp mode even after being cleared? Is there a capacitor in there that is keeping a powered memory alive, but may over an extended period of time, say a month or no of no power, finally clear?
Has the 13CUX ECU been permanently put into a limp mode? Could the 14CUX ECU suffer the same fate if I keep driving it until the new TPS arrives?
Things just get stranger and stranger...
 

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OK, got one coming, but interesting and troublesome side note:
I disconnected the TPS and drove around just to see what happened. The rig actually ran very well, started normal, ran and accelerated fine, no rich smell in exhaust, until..
The 13CU isn't getting a good TPS signal and the 14 won't change that. When the ECU loses signal from the TPS it's probably cutting fuel at out around 1500rpm that it knows from the coil. Check and see if it'll run with no MAF and no TPS, the former might be doing the latter's job until it reaches that cutoff point.

You've now gained diagnostic capability, but it wasn't an ECU issue to start with.
 

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Discussion Starter #9
Well yes, and no. I agree the 13CU was getting the same bad TPS signal that I still have, and the 14CUX did not fix the bad signal. However, if they are both getting the same bad TPS signal, then why does it run without the 1500 RPM cutout with the 14CUX, but will not with the 13CU??

The 13CU isn't getting a good TPS signal and the 14 won't change that. When the ECU loses signal from the TPS it's probably cutting fuel at out around 1500rpm that it knows from the coil. Check and see if it'll run with no MAF and no TPS.

You've now gained diagnostic capability, but it wasn't an ECU issue to start with.
 

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Well yes, and no. I agree the 13CU was getting the same bad TPS signal that I still have, and the 14CUX did not fix the bad signal. However, if they are both getting the same bad TPS signal, then why does it run without the 1500 RPM cutout with the 14CUX, but will not with the 13CU??
Might be something to do with how limp mode works between the two I'd suppose, nobody's really dug deep into the export 13CU.
 

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Well yes, and no. I agree the 13CU was getting the same bad TPS signal that I still have, and the 14CUX did not fix the bad signal. However, if they are both getting the same bad TPS signal, then why does it run without the 1500 RPM cutout with the 14CUX, but will not with the 13CU??
The 14cux self adjusts the tps.... you might find it cuts out at a different point.
 

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Discussion Starter #12
What I find odd about this is that I could not clear the 13CU so that the rig would run basically OK again, it would clear the EFI light, but not run worth diddly. Clearing the 14CUX ECU by disconnecting the battery not only cleared the code, but returned the rig to where it would run again without the 1500 RPM cutout.
I see how the lack of the TPS signal causes the 1500 RPM cutout (for some unknown reason, but who am I to question Lord Lucas??) but I don't see how the lack of a TPS signal, or a wonky signal could cause permanent ECU damage.
At this point, I am just going to go with the theory that the TPS signal was wonky and intermittent and it was coincidental that it would temporarily drop out and not be sending a signal when I tried the resets with the 13CU, thereby maintaining the 1500 RPM cutout issue. I agree that if I have a good TPS signal, the 13CU will most probably work fine, but I'm not curious enough at this point to re-install it just to see. Maybe when I get the issue totally resolved. Maybe.....
Merry Christmas and Happy Holidays to all!
 

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Discussion Starter #14
When it is in the 1500 RPM cutout mode, it will not rev over 1500, it's like you are turning the key on and off, but only while moving.
The hiccup behavior can happen at any RPM, and I have only experienced it while moving also.

I'm curious if it cuts out at a higher RPM. Have you run it higher the 2500 while driving?

Happy Holidays to you too and everyone else!
 

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Discussion Starter #15
Just a final (I hope) addition to this thread. The ultimate fix was not the new ECU, as symptoms returned. Ultimately it turned out to be a wonky TPS. I had replaced it a couple years back, and had tested it recently, but apparently not well enough. Installed a new one and all is well.
So weird that it seems to store multiple TPS failures and then goes into the "won't go over 1500 RPM" limp mode.
Equally strange that I drove it 100 miles or so back from the Guru and it ran fine. Gremlins I suppose...
I like the data access Rovergauge and the 14CUX provide, so while that did not fix the problem, I feel it was well worth doing.
Thanks for all the help and comments!
 
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