1990 3.9 Classic Starts - Runs - Stops

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Derek Ward

Derek Ward

Active Member
Posts
798
Location
Happily Ex Blackburn, Now Blairmore, Argyll & Bute
Hi Guys

I have a problem with my old Classic. I had a previous problem with it where it wouldn't start at all after someone had used it and virtually run it out of fuel. Changed the fuel filter, no difference. Removed the pump and found the connector burnt underneath the mounting plate. Replaced the pump assembly with a brand new one. Car would then start immediately but idle at 1800rpm rising to 2000 after 4 or 5 minutes and then die. It would not restart until the next morning when it was stone cold again.
I tried removing thje connectors for the fuel and water temperature and also for the cold start injector/Thermotime switch but this made absolutely no difference either way.
I then took the ECU in to my local Auto Electrical place who sent it off to their specialist for testing. It came back with no faults reported. (Tried to find a second hand unit first but they appear to be a bit thin on the ground).
Installed the ECU back in the car which again started immediately (with all sensors connected) but this time idling correctly at around 800rpm or so. It did this for 4 or 5 minutes again until it was starting to warm up and it then died as before. Plug removal after cranking showed them to be completely dry. Each plug has been tested for giving a spark and is OK.

There appears to be activity on the connectors for the fuel injectors so I'm guessing these are being fired by the ECU

There is fuel being pumped up to the rail with plenty of pressure from the pump but I don't know how much pressure there is in the rail itself. Is there a way of measuring this without specialised equipment?

Next step is to try and get hold of another fuel pressure regulator.

Anyone had this before?

I have the manuals for up to 1989 models but the ECU is different with a different connector. Does anyone have the pinouts for the one on my car (PRC 8702). The copy of Rave I have has the info for a 1995 Classic which is different again.

Any suggestions appreciated

Desperate Derek of Blackburn
 
Have you replaced things such as, stepper motor, penometer, CTS (coolant temp sensor) ??

These where all suspect when I got my 3.9 and the idling story you have is very similar to mine.
It would also run ok when cold, but when warm it would cough and splutter due to the CTS being at fault.
Also check your air intake hoses for any holes or leaks as it might be letting in "free" air to the system which can cause the idle/running problem.
 
as above and if it really is temp related it could be the amp playing up as they dont like the heat but I wouldnt have thought it could get that hot in 5 mins.

in the haynes there are some revisions for the hotwire 14 cux injection system but they are not where you would want them but it is in there.

stu could sort this in an hour or two but he is on holiday for a couple of weeks I think. ring him when hes back ant it will be sorted for you.
 
Hi guys
Sorry for the delay in coming back.

Yesterday, got it running and then removed the MAF sensor plug. Idled a bit rough but did stay running for over half an hour. Plugged the MAF sensor back in and it stopped within 4 or 5 minutes. Wouldn't restart again.
Went to it this morning. Wouldn't start (with MAF plugged in). Removed plugs and all wet. Dried off and started OK. Removed MAF sensor plug and again kept on running for 25 minutes. So, it looks like the MAF sensor. Any way of checking these other than by substitution?
Just for a laugh, I've priced a genuine one from Land Rover - £1139+VAT! And, it's an extra £70 if you don't send your old one back! Unbelievable.
My Indie reckons that MAF sensors can deteriorate when not used. Old wives tale?
Anyway, if I can't find a known good one, it'll have to be a britpart or something.
I'm back at work offshore Brazil tomorrow so I'll have to continue this when I get back in 5 or 6 weeks. Thanks for the help and suggestions.
Cheers
Derek
 
Derek Ward said:
Hi guys
Sorry for the delay in coming back.

Yesterday, got it running and then removed the MAF sensor plug. Idled a bit rough but did stay running for over half an hour. Plugged the MAF sensor back in and it stopped within 4 or 5 minutes. Wouldn't restart again.
Went to it this morning. Wouldn't start (with MAF plugged in). Removed plugs and all wet. Dried off and started OK. Removed MAF sensor plug and again kept on running for 25 minutes. So, it looks like the MAF sensor. Any way of checking these other than by substitution?
Just for a laugh, I've priced a genuine one from Land Rover - £1139+VAT! And, it's an extra £70 if you don't send your old one back! Unbelievable.
My Indie reckons that MAF sensors can deteriorate when not used. Old wives tale?
Anyway, if I can't find a known good one, it'll have to be a britpart or something.
I'm back at work offshore Brazil tomorrow so I'll have to continue this when I get back in 5 or 6 weeks. Thanks for the help and suggestions.
Cheers
Derek
Click to expand...

Sounds promising but be careful!! I had a running problem with my 3.9 turned out to be an iffy ECU that wasn't reading the MAF. Normally, if teh MAF was not right I would have thought the EFI warning light would come on, it certainly should if you disconnect the MAF. If the warning light didn't come on make sure it is not a gremlin in the ECU or the EFI harness.

I know you said yourECU was tested, I did the exact same thing and I had the MAF checked too, both came back "No Faults Found" I really would go down the test by substitution route. I have a spare MAF and ECU but I think I'm a bit too far away. I did run mine round with the MAF disconnected for a while but I was getting about 6mpg!!
 
try martin toole for a maf he should have one, there are often ones on ebay too. in fact ragtag on here had one for sale not long ago, he might still have it!
 
Hi Guys
Apologies again for delay in coming back - been travelling back to work.
Classic kev - Understand what you're saying re the ECU and MAF and trial by substitution. I was trying to get hold of an ECU before I sent it for 'testing' but couldn't find one at the usual breakers. This model seems a bit thin on the ground for ECUs as they changed in 1991 I think to the 14cux ECU for use with the catalysts. Anyway, I'm due back home around the middle of November so I'll start looking for a MAF sensor nearer the time - maybe post on here first to see if anyone has one near where I live.
What about this report from the Indie that he thinks they deteriorate over time if not used?
Fett - I think I have Martin Toole's number but who's ragtag?

Cheers
Derek
 
just send a message to ragtag on here , thst his user name. nice guy with a bobtailed classic, he had one he was gonna sell.

I think the 14 cux ecu's are all the same, thats what I was told
 
Derek Ward said:
Hi Guys
Apologies again for delay in coming back - been travelling back to work.
Classic kev - Understand what you're saying re the ECU and MAF and trial by substitution. I was trying to get hold of an ECU before I sent it for 'testing' but couldn't find one at the usual breakers. This model seems a bit thin on the ground for ECUs as they changed in 1991 I think to the 14cux ECU for use with the catalysts. Anyway, I'm due back home around the middle of November so I'll start looking for a MAF sensor nearer the time - maybe post on here first to see if anyone has one near where I live.
What about this report from the Indie that he thinks they deteriorate over time if not used?
Fett - I think I have Martin Toole's number but who's ragtag?

Cheers
Derek
Click to expand...

Derek,

Should I take it yours is a flapper and not hot wire? I was under the impression all 3.9's were hot wire. The 14CUX ECU was used on non-cat vehicles, the chip holds both cat and non-cat maps in it and they are selected by swapping out the tune select resistor.

If yours is a flapper, from what I have read, the MAF can play up, something to do with the spring on the air flap or something, a repair is possible but not all that reliable in the long term. I have also heard that the ECU on flappers do suffer from problems with internal corrosion; after all they are all now 20 + years old.

Let us know how it goes when you get back.
 
Aah, that's what the tune select resistor is for! As Fett says, the 3.9's are all Hotwire. The 3.5's were flapper with a different ECU. Then they went to a hotwire on the 3.9 with the same ECU as mine and then to the 14cux ECUs. Landrover have the 2nd generation 14cux ECU as a direct replacement for mine but I'm sure mine doesn't have any tune select resistors in anywhere. I have the manuals for the 3.5 up to '89 and Rave is for the '95 vehicles. I'll try to get hold of a haynes for my year in the next few weeks.
I'll get the bugger going eventually, then the real fun (and expense) starts with the welding.:D:D:D
 
Derek Ward said:
Aah, that's what the tune select resistor is for! As Fett says, the 3.9's are all Hotwire. The 3.5's were flapper with a different ECU. Then they went to a hotwire on the 3.9 with the same ECU as mine and then to the 14cux ECUs. Landrover have the 2nd generation 14cux ECU as a direct replacement for mine but I'm sure mine doesn't have any tune select resistors in anywhere. I have the manuals for the 3.5 up to '89 and Rave is for the '95 vehicles. I'll try to get hold of a haynes for my year in the next few weeks.
I'll get the bugger going eventually, then the real fun (and expense) starts with the welding.:D:D:D
Click to expand...

So what ECU have you got to run hotwire? 14CUX is the only one I think that was used for this system. From what you posted before, either the MAF is playing up or the ECU is shot. Have you tried testing the MAF with a multi meter to check the output signal voltages? This might be a good place to start; values can be found in Haynes.

If MAF appears to be good then check out ECU by substitution, if MAF readings are a bit iffy, substitute MAF and see what happens.
 
I'm at work at the moment but off memory, the part number is PRC8073 but I see in the classic parts catalogue on disc that it lists it as PRC9061 (It doesn't mention the 14cux bit which is a Lucas number). I gather that the later 14cux will work on mine.
I've just ordered a haynes book from Ebay so that should be home when I get back in a few weeks. I'll test the MAF then.
It looks from Rave that the tune resistor goes to Pin 5 of the ECU connector and then to earth. Can't see any resistor values though. Any idea what they should be?
 
if its a 1990 it wont have cats, just leave the tune select resistor in the loom and plug in your replacement 14 cux ecu.

all range rover hotwire had a 14 cux ecu
 
Derek Ward said:
I'm at work at the moment but off memory, the part number is PRC8073 but I see in the classic parts catalogue on disc that it lists it as PRC9061 (It doesn't mention the 14cux bit which is a Lucas number). I gather that the later 14cux will work on mine.
I've just ordered a haynes book from Ebay so that should be home when I get back in a few weeks. I'll test the MAF then.
It looks from Rave that the tune resistor goes to Pin 5 of the ECU connector and then to earth. Can't see any resistor values though. Any idea what they should be?
Click to expand...

I'm pretty sure that part number is a 14CUX. Non-cat uk spec tune select resistor should be 470 ohm from memory (would need to check that though) and cat spec is 3900ohm I think. If you do a search I think I have posted on that somewhere and also on ECU part numbers but that was some time ago.
 
Cheers Fett / Kev. Your help and advice is much appreciated. It's just frustrating being stuck out here and not being able to do anything for a few weeks. (Allthough some of the spectacularly curvey scenery that moves on it's own does make up for it now and again:D:D:D) Back to reality and expense in November:(:rolleyes:
 
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