More problems, my classic hell

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fett

fett

Well-Known Member
Posts
8,637
Location
South Hampshire
Well after putting a new boot floor in ,patching the rear inner wings, replacing the corner of the bonnet with new steel, new wiper motor and mechanism, new headlining , two new tyers , a jack and parcel shelf etc and service items about £900+ total cost for the rangie and parts and it will need a new rear crossmemberfor MOT, the engine has now started playing up!

Its a 1990 3.9 efi v8.

From previous efi experience I think I have two problems which started coincidently on the same day.

First when strated from cold and now from hot (but much worse from cold) it will only run on 6 or 7 cylinders till it warms up (about a mile).

Second it will not idle properly , it often dies first start when left to idle , it then hunts especially after you rev it to keep it going. the idle when it is going is sometimes fine but othertimes too low, ocasioanally to a stall.

I have replaced all the leads cap and rotor with new lucas parts and the plugs with champions, when I got it 8 weeks ago as it was complaining a bit then and all has seemed fine untill now weeks later.

Please help, I need ideas.

My first being to weigh it in lol.

Thanks

John
 
take the stepper motor out and give it a good clean with carb cleaner or mister muscle oven cleaner.also change the ecu temp sensor, that little 10 quid sensor can cause a lot of problems
 
Is the stepper motor what I would call an idel control valve on a bmw, to by pass air at idle?

Is it whats on the back of the intake manifold sticking out of the drivers side?

Wheres that temp sensor located?

I have just had a thought, I disconected the battery to do all my welding, does it take a few days for the ecu to learn its perameteres again like some of the old BMW did?

Thanks

John
 
yes the stepper sticks out the drivers side of the inlet manifold.
the ecu temp switch is on the top front of the inlet manifold,
as for the fuel ecu on a classic, it 10 minutes unconnected for it to recalibrate itself.
i think its the temp sensor and/or the stepper motor playing around.
 
Thanks I will have a look tomorrow, would they account for the missfire?

Do you mean it only have to be disconnected for ten mins then it will need to reacalibrate its self, as it was disconnected for a couple of days.

It does seem to be alot better today than the last few days, hasnt missed hardly atall or stalled more than once , I really dont know what to think lol.
 
sounds like damp got into the dizzy cap, whip it off and wipe a clean cloth in there, as for the fuel injection ecu, if it plays up, just disconnect it for ten minutes, and it recalibrates itself. leaving battery off for any amount of time wont affect it.,
also check all the leads are pushed on to cap tightly and at the spark plug ends.and coil.
let me know how it goes
 
Hunting revs could be anything really. On our rangies we have cured it with 2 different thing son different cars...one time it was the ECU at fault...second time it was the small vacuum unit (sorry dont know the name of it, it is located on the bulkehad to the left of the block) which was causing to hunt revs and missfire.
 
Why , are you thinking head gasket then? its not a 4.6 lol

It really has improved on its own and the it hardly misses at all (although none would be better.) the main thing about the running thats bugging me is that about 90 percent of the time it idles way too low at about 250 rpm but the other ten percent its fine at about 700. It also hunts abit on start up on occasion.

It seems too low more often when its in drive after I come of the throttle, if I come in to neutral they pick up and back into drive and they stay at the correct level. very odd!

Obviously a good place to start would be the idel control valve as I call it , or the stepper as you green oval experts call it and suggested. I went to buy carb cleaner today, we only have two car parts places left in town (thanks mr brown) motorworld and halfords and niether had any,the girls in halfords said it goes out almost as soon as its in , kids sniffing it these day I suppose?

Would acetone do the job? I can get lots of that and I thought some splashes of that and a fitch would clean it.But I dont want to melt it!
 
you really need some carb cleaner in that tool kit of yours.buy a tin off ebay.and give the plenium chamber a nice spray, especially the throttle butterfly, i tend to put the handle of a screwdriver in the butterfly, spray a nice load in, then leave it open so all the crap flows out.
mister muscle oven cleaner will clean the stepper valve nicely, and to me it sounds as though that is the problem. but as i said, classics need to be used, the more they are driven the better they behave.
 
Finally it got here today. thats the only draw back with ebay-delivery time.

I will have a crack tomorrow if it stops raining for an hour.

Does that air bypass valve unscrew or just pull out?
 
SUCCESS!

I took it out , the washer fell into 3 bits before I had even finished unscrewing so I made one out of an old castrol can , cleaned the valve and the hole with 3/4 can of carb cleaner , put it all back together and it started rough and was smokey but once it burnt off the crap it seemed to run and idel good , Only tried it once so far but I will keep you posted.

Thanks for all you help , especially mr 1992lse
 
very welcome. glad it has seemed to have worked. forgot to mention that it will run like a bucket of ****e at first.hope your heart didn't pound too hard.
happy classic motoring.
 
Spoke too soon,doh! Its not really bad but it still seems too slow at idle about half to a quater of the time , but not as lumpy as it was.

I tried adjusting the base idle with the allen screw but after working my way up to 3/4 of a turn to a full turn no difference in the idle speed but when revved and coming down off the throttle it sounded like small missfires in the exhaust , I put the idle screw back and they go away.

It was definatly the idle speed screw I adjusted by the manifold not the one on the airflow sensor.

Any ideas on that one guys?

PS, I hope my rev counter is right as it seems to sound right when idling at 500 rpm , I am calling it too low at 250 rpm but the book says it should be 700rpm?
 
A frustrating problem! You've checked and cleaned the stepper motor - this is good. You say you have checked and set base idle. Have you checked that your vac advance is working properly?

It might be worthwhile taking off and cleaning the plenum and ram housing and then re-assembling, check carefully there are no vacuum leaks and all hoses are in good condition. Check condition of ignition leads/plugs/dizzy cap and rotor arm. Re-set base idle.

I once had a problem with ignition timing wandering about a bit as a result of a stretched timing chain. Have you checked where your ignition timing is?

Look in Haynes/Rave and run ignition system tests to make sure all the components are doing what they should. If you are satisfied there is not an ignition problem you may be looking at an injection misfire but the symptoms don't sound quite right for that.

Hope that helps ya.
 
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