ECU problem - part number query

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rojbarker

rojbarker

New Member
Posts
544
Location
Handover, 'Ampshire
Hi there,

I've got a cold-running issue with my 87' 3.5 efi. I bought a replacement ECU from someone and fitted it. It runs worse than ever! Misfiring, popping back, no power, hunting idle. Forgot the mention, the seller only removed it from theirs to fit a 4 barrel carb and said it was running fine before so it may not be the new ECU.

My old ECU was PRC 4764 model 84477B. The replacement was same part number, model 84477D. Should I be able to use it? I must admit, when I fitted the new one, I didn't bolt it to the chassis but left it on the carpet (I was expecting to have to change it back!) Does it use the chassis as earth?
 
rojbarker said:
Hi there,

I've got a cold-running issue with my 87' 3.5 efi. I bought a replacement ECU from someone and fitted it. It runs worse than ever! Misfiring, popping back, no power, hunting idle. Forgot the mention, the seller only removed it from theirs to fit a 4 barrel carb and said it was running fine before so it may not be the new ECU.

My old ECU was PRC 4764 model 84477B. The replacement was same part number, model 84477D. Should I be able to use it? I must admit, when I fitted the new one, I didn't bolt it to the chassis but left it on the carpet (I was expecting to have to change it back!) Does it use the chassis as earth?
Click to expand...

Nope - it is earthed to the engine via the loom. You can check the earthing as well, but the space there is pretty tight. Watching from front of the engine - right hand bank, behind. I reached the two bolts from behind. If I remember correctly the earth was bolted to the head. I have no idea on the ECU models.

Why do you think the seller of the ECU changed to carbs? Did you see/hear the car running well?

If you have a friend with a known good ECU in a perfectly running car, check your car with it - probably the chaps around here can help in this one.

Oh - almost forgot: Have you changed the coolant temp sensor yet? I'd fit a new one first.
 
I'm sure all my earth straps are connected. I just wondered if the case of the ECU was earthed via the mounts when it is fitted correctly. Maybe I need to let the ECU tune itself in or something?
The seller assured me it was fine in his 86' 3.5. He changed the ECU as he was fitting a 4 barrel holley and mild road cam - was selling all the EFI parts. I have no reason to believe he's lying.
I probably do need to change some other sensors - kind of hoped that the ECU was the problem!
 
A few guys on here directed me towards the ECU. Aprantely those Lucas boxes are known for playing up. But it made sense to change the ECU to a good one then see what happens. Obviously it didn't work out as well as I hoped!
 
clutchdust said:
ECU's rarely go wrong, it's more than likely the idle air control valve thats blocked with crap or a temp sensor/AFM fault, something like that.
Click to expand...
t

I disagree. At least here in Finland the most common thing to bust is coolant temp sender, then ECU. I have not heard of any AFMs to go wrong - yet. Both the hotwire and flapper idle air control valve systems may need some cleaning occasionally. The flapper one especially, being very simple, is almost bulletproof, although prone to gather crap inside it.

On my previous RRC (VIN: CA), the ECU was the one giving trouble. Coolant temp sender was okay, as well as AFM, TPS, IAC-valve, injectors (including the extra cold start injector). Also the ignition system with ECU-engine speed feed was fine. I tried, cleaned and swapped everything with known good ones, but ended up buying only a new coolant temp sender and ECU.

Well - I did not check the inlet manifold gasket thoroughly by removing the inlet manifold, but it did not leak.

The trouble was poor idle, engine dying occasionally, when cold. It improved gradually when the engine temp went up.

I do not know whether the trouble here is the huge temperature differences between summer and winter. Badly soldered connections inside ECU were the troublegiver. I have heard a lot of these cases here, as well as the coolant temp sender being busted. All of the cases had similar symptoms.

First I would change the coolant temp sender (it's cheap), then check ignition, then for airleaks in any of the pipes and also clean the IAC-valve (and engine breather hose). These ones are cheap and easy.

Do you have any trouble with brakes?
 
No all the brakes are fine. The only thing is the cold running problem. If you floor the gas when first started, the engine will stop and die if you hold it down. I had the valley gasket done recently. Probably is a sensor but wanted to rule ECU out first.
Anyone got any reason the new ECU makes the car run even worse than the current one?
 
I recently had the same issue with my 86 classic 3.5. Having done all the diagnositc checks on the ECU, water temp sensor, air flow meter ect. I changed the ignition module on the side of the distrbutor. Now ticks over and runs like new!
 
The old 4cu ECU's do fall over in old age,hunting and poor idle are both common,dont see many now but I still keep a known good ecu on the shelf cos its a quick sub over to check.They all seem a bit different in the way they make the engine run,remember the first ones off the production line wouldnt even start - they towed them off the line.The Hot wire system was much better.
 
Maybe I'll try sticking it in again and see what happens.

Then I'll check the fuel & coolant temp sensors.

Then the ignition module on the dizzy - although it does run fine when warmed up so not sure that will help. Anyone got a part number for one or does it depend what distributor I'm using?
 
rojbarker said:
Maybe I'll try sticking it in again and see what happens.

Then I'll check the fuel & coolant temp sensors.

Then the ignition module on the dizzy - although it does run fine when warmed up so not sure that will help. Anyone got a part number for one or does it depend what distributor I'm using?
Click to expand...

Flapper does not have fuel temp sensor.

The coolant temp sensor is cheap and should be changed if suspected faulty. If you don't want to spend money on it in vain, you can easily measure resistances with coolant temp change from the ECU loom (or the at the connector) with a multimeter. The values should vary from 1.5 kOhms when cold to 200 ohms or so when warm.

I would also check carefully for airleaks around the inlet manifold (especially since the inlet manifold came off recently) and plenum chamber - as well as around the dizzy vacuum unit and brake servo.
 
rojbarker said:
Maybe I'll try sticking it in again and see what happens.

Then I'll check the fuel & coolant temp sensors.

Then the ignition module on the dizzy - although it does run fine when warmed up so not sure that will help. Anyone got a part number for one or does it depend what distributor I'm using?
Click to expand...

Range Rover Classic--Electrical

This may help in your search for the ignition module, I think your module is next to the coil on the 3.5.
 
TimoV said:
Flapper does not have fuel temp sensor.

The coolant temp sensor is cheap and should be changed if suspected faulty. If you don't want to spend money on it in vain, you can easily measure resistances with coolant temp change from the ECU loom (or the at the connector) with a multimeter. The values should vary from 1.5 kOhms when cold to 200 ohms or so when warm.

I would also check carefully for airleaks around the inlet manifold (especially since the inlet manifold came off recently) and plenum chamber - as well as around the dizzy vacuum unit and brake servo.
Click to expand...

Wonder what part I've bought then? It was £30 as well! There are 2 sensors near the fuel rail, in front of the intake plenum. One is bigger than the other and both I think have brown 2-pin connectors on.

I'll have a look for leaks too. Trouble is it's getting dark so quickly now, no time to have a poke around after work! Thanks for the advice.
 
rojbarker said:
Wonder what part I've bought then? It was £30 as well! There are 2 sensors near the fuel rail, in front of the intake plenum. One is bigger than the other and both I think have brown 2-pin connectors on.

I'll have a look for leaks too. Trouble is it's getting dark so quickly now, no time to have a poke around after work! Thanks for the advice.
Click to expand...

The other one is the thermotime switch, and is more expensive than the CTS (£7.50 excl. VAT at Paddocks). It is in front of the coolant temp sensor. Almost totally useless in UK - it steers the cold start injector connected to left side of the plenum (looking from front). The coolant temp sensor is more difficult to change due to reachability problems - if I remember correctly the TTS, as well as the top hose, needs to come off when replacing the CTS. Be careful with the connectors, they break easily.

The 9th injector is useful here in Finland where the winter temperatures can get to -30oC. Oh - it may also leak, causing running problems when warm. This one you can simply check by removing it carefully and pressurize the fuel rail by having ignition on and gently moving the air flap in the AFM (remove the downstream hose and you can see the flap, which you can push open). This turns on the fuel pump and the fuel rail pressurizes. You should then see if the injector leaks.

The air-leaks you can track with the starter fluid sprayed around the intake while the engine running. Spray on one area and listen. If you get higher idle you have an air-leak nearby.

The ignition module is attached to the side of the dizzy -87 onwards (DA-). Earlier it was under the coil.

PS: Perhaps you should type "Land Rover Manuals" into Google and download the parts covering RRC from the first links that appear in the results.
PS2: I got rid of my 3.5EFI (CA) a year ago and bought myself a 3.9:er. Guess why.. :D
 
On the CTS note, i have just replaced mine on my 3.9 EFI, not sure if it's in the same place but it's not that hard to get to, Make sure you have an extension on a rachet, i think i used a 22mm or close to it. Just dont over tighten. You need to slip the extension behind the big water hose and this will let you in at it.

This is where mine is.(the pic is an old pic of my poor leads and dizzy cap)

DSC01600-1.jpg
 
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