Heres one for ya

Some of you will remember me posting things a bit like this months ago, but I have come a little further on with it,delayed only by other bits of the rangie breaking!

Its a 1990 3.9 classic on petrol (and lots of it!)

First thing in the morning if I just get in it and drive it its doesnt run on all cylinders for a while and although not missing cylinders when Idling it idles too low straight after you turn the key then picks up for about 5 mins but again for the rest of the day it idles a bit too low.

If you leave it to idle on the drive for 2 mins before you drive its on all cylinders but will often idle lumpy and a bit too low, mybee 3-400 rpm espcially when in drive. The handbook says not to let it idle but to drive it asap.

I have fitted new plugs, leads, cap ,rotor (all lucas), air filter, fuel filter, fuel tank, airflow meter, and today a new airbypass valve. all make no difference.

With the valve , if the car is idling and you unplug it it makes no difference, is that right?(paddocks sent me britpart)
I am only getting 9.3 mpg round town and 12.6mpg on the motorway at 65mph

I have had it at two garages ( one was monkey mans though, some of you will remember his mistakes) and the co2 and Hydrocarbs are both good and low like0.3.

The plugs are a bit black but not terrible so that is probably from my town driving.

I have bought a ecu water temp sensor but am reluctant to fit it incase the old one sheers off.

Any other sensors to change and where are they, or anything else to try?

Any help greatly appreciated as I want it to run right and mpg is killing me!:doh:

black wet or black sooty?

sticky injector?

Black sooty, not that bad I have been told.

How would I test for the injector?

What about the bypass valve, should it make a difference at idle if unplugged?

where is the water temp sensor located? if its located in aluminium, boil a kettle full of water, pour it over the area and gently 'crack' the nut!!

Is it on its original cam?

I did a fair bit of research on the Rover V8 and most sources seem to contend that camshaft wear and timing chain stretch are big contributors to uneven running/power loss/ heavy fuel consumption etc etc after 125,000 miles or so (depending on previous care obviously).

My own one (on which I've had the cam changed at 140,000 miles) is running a bit rough again but I've it down to one of two things:
1. Sticking stepper motor
2. Fecked ECU

The ECU is constantly returning a low value for coolant (even though I've chnged the sensor and the temp guage works perfectly) which is causing the ECU to thinks its constantly cold thereby running it on the cold fuel map and timing. Symtoms are high idle/slow to drop and complete no start when hot if it doesn't catch on first few turns (flooding I think). Its a peach to start from cold.

Well it could well be on its original cam, It is a quick rangie , not that I can afford to try that often but it could be gaining top end performance at the expense fo low end conrtrol Its milled itself a race cam lol

How do I check which fuel map its on?

Buy a scrap one off ebay. Probably in better nick though

Khryztal said:

Buy a scrap one off ebay. Probably in better nick though

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Good come back mate, just a bit slow lol

fett said:

Good come back mate, just a bit slow lol

Click to expand...

Was listing some poly bushes on eBay. :lol:

:doh: lol

I need some answers peeps, come on!

Sorry. forgot the question

Hi Fet,

Before you unnecessarily spend more money, preferably while motor is cold as this is when you say problem is occurring, have you had your car somewhere where there is no light (total darkness is best) and checked under the bonnet with the motor running, looked around all plug and coil leads for intermittent faint bluish glow or sparks, your list does not include the coil, have you had a good look around it as well at same time.
Won’t cost you much.

fett said:

If you leave it to idle on the drive for 2 mins before you drive its on all cylinders but will often idle lumpy and a bit too low, mybee 3-400 rpm espcially when in drive. The handbook says not to let it idle but to drive it asap.

I have fitted new plugs, leads, cap ,rotor (all lucas), air filter, fuel filter, fuel tank, airflow meter, and today a new airbypass valve. all make no difference.

With the valve , if the car is idling and you unplug it it makes no difference, is that right?(paddocks sent me britpart)
I am only getting 9.3 mpg round town and 12.6mpg on the motorway at 65mph

I have had it at two garages ( one was monkey mans though, some of you will remember his mistakes) and the co2 and Hydrocarbs are both good and low like0.3.

I have bought a ecu water temp sensor but am reluctant to fit it incase the old one sheers off.

Any other sensors to change and where are they, or anything else to try?

Any help greatly appreciated as I want it to run right and mpg is killing me!:doh:

Click to expand...

I think I would be tempted to check ECU by substitution; if you know anyone with a known good spare ecu, plug it in and see what happens.

If you do a search, I recently saw a thread that explained a way of testing and cleaning the stepper motor so you should be able to check that out.

Somebody suggested stretched timimg chain - could be. There are a couple of "tests" for that; one is to get it to idle and stick a strobe light on it, then blip the throttle and generally mess with it and let it come back to idle, if the timing keeps changing at the idle speed chain is probably stretched (been there done that). The other method I have used to checking slack in the timiing chain involves the bottom end of an old distributor. Take the dizzy out, insert homemade adapter and rotate back and fore, you can feel excessive slack in the chain.

If your ECU was over fuelling you would not get 9 - 12 mpg. It would be more like 6 - 8 I would think and certainly it would be this low if your ecu has gone into limp mode. Also, if a sensor dies, it should be picked up by the ecu and the EFI warning light should come on.

Have you checked for any induction leaks?

A compression test might also be useful just to confim all pots are up to pressure and should therefore burn correctly.

Good luck.

One other thought, slacken the distributor clamp nut so you can turn the dizzy. Start the engine and see if advancing or retarding the timing makes any difference but make sure you mark the original starting point so you can put it back.

ssmn1234 said:

Hi Fet,

Before you unnecessarily spend more money, preferably while motor is cold as this is when you say problem is occurring, have you had your car somewhere where there is no light (total darkness is best) and checked under the bonnet with the motor running, looked around all plug and coil leads for intermittent faint bluish glow or sparks, your list does not include the coil, have you had a good look around it as well at same time.
Won’t cost you much.

Click to expand...

That was my next plan as its free!

classic kev said:

One other thought, slacken the distributor clamp nut so you can turn the dizzy. Start the engine and see if advancing or retarding the timing makes any difference but make sure you mark the original starting point so you can put it back.

Click to expand...

Yeah I have had the timing checked and it is advancing ok and the diagphram is ok thanks for the idea

Are the plugs for the fuel rail temp and coolant temp swapped?
Have you done a compression test ?
Does it run Oxy sensors/Cats ? Probably not at 1990,but we need to know.
Has the fuel rail pressure been checked to see that it goes up and down according to demand ?

classic kev said:

I think I would be tempted to check ECU by substitution; if you know anyone with a known good spare ecu, plug it in and see what happens.

If you do a search, I recently saw a thread that explained a way of testing and cleaning the stepper motor so you should be able to check that out.

Somebody suggested stretched timimg chain - could be. There are a couple of "tests" for that; one is to get it to idle and stick a strobe light on it, then blip the throttle and generally mess with it and let it come back to idle, if the timing keeps changing at the idle speed chain is probably stretched (been there done that). The other method I have used to checking slack in the timiing chain involves the bottom end of an old distributor. Take the dizzy out, insert homemade adapter and rotate back and fore, you can feel excessive slack in the chain.





If your ECU was over fuelling you would not get 9 - 12 mpg. It would be more like 6 - 8 I would think and certainly it would be this low if your ecu has gone into limp mode. Also, if a sensor dies, it should be picked up by the ecu and the EFI warning light should come on.

Have you checked for any induction leaks?

A compression test might also be useful just to confim all pots are up to pressure and should therefore burn correctly.

Good luck.

Click to expand...

Ok just spent an hour reading old stepper motor posts, with no luck .

Regarding just the stepper for now what I need to kow is: If I unplg the wires with the engine at idle should it make any difference?

as I want to send this new ****part one back to paddocks before they say I am not allowed to return it.

Keep the ideas coming!