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westonben

3.9 Bad Idle

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Roger Threesheds' very informative post contained something that you may have missed.

Rogue Air Leaks into the plenum make it impossible for the ECU to run the engine other than at startup because it cannot control the overall mixture.

If there is an airleak then no matter how many components have previously been replaced the cost will have been in vain.

Such checks often need to go beyond beyond normal physical inspection and on my much earlier flapper system there is a set procedure which you may be able to adapt.

You can see that process in the PDF available from here

http://www.vintagemodelairplane.com/pages/...l/Plenum01.html

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Ramon, the details in that link look really interesting but what's the problem with trying to read it as for me it's print over print etc & mainly indecipherable? Is it my settings or is it the site?

I would like to read a lot more, but can't see how to.

Thanks

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Ramon, the details in that link look really interesting but what's the problem with trying to read it as for me it's print over print etc & mainly indecipherable? Is it my settings or is it the site?

I would like to read a lot more, but can't see how to.

Thanks

Hello Fleet, As far as I know the site is not misbehaving and I've had no similar reports so it is probably your browser or Adobe reader settings.

Are you having problems with the HTML page or opening the PDF?

If its the PDF I can send it to you by email or likewise on .doc format for MS Office

Let me know your Email address thro the Contact Me page on my website or by PM.

I'll get it to you what ever it takes.

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Thanks Ramon. It's on it's way & I have included a Screen Print of said "problem". :rolleyes:

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Thanks Ramon. It's on it's way & I have included a Screen Print of said "problem". :rolleyes:

Hello Des, I think the problem is screen resolution. i'm assuming you have a version of internet explorer

From what you said you appear to have read the Plenum PDF but if not i have mailed it to you along wth a another fuller test program pdf and one on exhaust systems just for interest..

To check your resolution right click on your desktop, click properties, click the settings tab and note the existing resolution.

then adjust the slider to a different setting and ok out to try the jumbled pages again. if no luck and it mucks things up reset it to the original

you may need to reset internet explorer or you may have a system bug,

There are over 180 pdfs on the site so it would be impossible to email the whole set, but if you still cannot access the archive try looking at the site on another computer - friend/work whatever - and see if it behaves there.

If it does and you eyeball a few PDF you need then I will forward them, but the best route would be to see if you can fix the bug.

Ramon

www.vintagemodelairplane.com

ps I just interrogated my site stats and it appears you are using firefox 3 0.4, with a resolution of 1024 x 768, that should be ok but I am not at all familiar with how ff works but I have not received any comments. i will try to access the wobbly page with my version of ff and see what happens.

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Not really, it just means that it won't be adjusting the idle when different loads are applied as it should -if you load the engine with it disconnected (fans, heated front/rear windscreen, put it in D with the hand brake on, AC on) it should drop and not recover. With it connected it should maintain the idle speed, or at least something close to it!

Bowie69,

I understand your point now, sorry. Will try this out tonight. I suspect that the car will behave exactly same with it unplugged than plugged, but we'll see.

I once forgot to connect the stepper and took it for a drive and I didn't notice a difference! A few things have changed under the bonnet since then....

Ben

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For general info.

The site concerned, when viewed in Internet Exploder is now fine for me. FFx, not so rosy.

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It's an old one I know, but I'm at my wits end with it.

I've got a gulf spec, 3.9 V8 EFi 1999 Series 1 Auto (non Cat). I've had a 6 month long-running problem with the idle being erratic (pull up at lights to have the revs dip, and usually recovery, also, low speed driving sometimes a problem with low revs.

It's got the Lucas 14CUX hot-wire and now most of that is new.....

I have replaced:

Fuel pump

Fuel Filter

Leads - Magnecore

Rotor Arm, Dizzy Cap, - Genuine

TPS

IAC (Stepper)

MAF

Coolant Temp Sensor

I'm sick to death with the problem and just can't diagnose the problem properly here. I'm in Qatar and the local main dealer hasn't been able to fix the problem, they have reset everything and whilst it's certainly running smoothly, it just doesn't always idle right.

My last remaining items to try (in order) are:

Fuel Temp Sensor

Coil

VSS

Anyone else got any other ideas before I drive it into the sea?

Thanks

Ben

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Peter,

Not sure the point of your post, but if it's to suggest I haven't ruled out the Vacuum then you missed the post quoted below:

Thanks for the great suggestions, I've a few things to look at there. Should have mentioned I've been right round her with carb cleaner and found nothing to suspect vacuum.

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Right, I've double checked the breathers for vacuum, there's not problems all round the plenum.

I've been out for a run this morning, and apart from the coolant leak, the car runs perfectly. Only problem is when slowing down. I can get it to nearly stall if I accelerate and quickly stamp on the brakes. It seems to be starting no problems now.

I tried to do the ECU checks, but it's beyond me really. I couldn't even get the multiplug disconnected!

I am going to try a new coil and a new fuel temp sensor...... What would be the symptons if one of those were failing?

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Hi, i had this problem with my 3.9 defender a couple of weeks back. it turned out to be the air flow meter. a £40 second hand replacement solved it instantly without having to reset anything.

Good luck, Steve

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Hi, i had this problem with my 3.9 defender a couple of weeks back. it turned out to be the air flow meter. a £40 second hand replacement solved it instantly without having to reset anything.

Good luck, Steve

Yes, I still am considering it could be the MAF. I replaced mine with a pattern one off ebay so it could well be dodgy. Just can't face the price tag over here (£1000). I may get one back in the UK when I'm there for xmas.

I suspect you didn't have to reset anything because it's got O2 sensors controlling the CO trim?

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Having an Auto Elec or tuneup place shove a probe up the exhaust would tell you if the MAF is faulty. It may simply need adjusting, or like my 13 year old one had run out of adjustment & no matter what they did, they couldn't bring it back to specs.

It would pin it down & make your decision easier & more positive.

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Having an Auto Elec or tuneup place shove a probe up the exhaust would tell you if the MAF is faulty. It may simply need adjusting, or like my 13 year old one had run out of adjustment & no matter what they did, they couldn't bring it back to specs.

It would pin it down & make your decision easier & more positive.

I took it to Bosch and got it tuned within specs a couple of weeks back. I thought maybe the reading could be jumpy though?

Really don't know where to go with it at present....

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One would assume they would have tested it thoroughly?

Still, if in doubt....................... get the probe stuffed up it by someone else & see. Or get hold of a loan one. If you don't prove it now, & just drop a new one in, you could still finish up with the problem & quite a few quid short.

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The problem I have is that Bosch are the only place in the whole country who have the equipment to do the analysis and they didn't seem totally up on what I was asking of them.

I guess I have to assume it's ok and try the coil/fuel temp sensor.

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I'm not going to read through the 40 posts, but have you done the old "twist the MAF pins" trick?

That cured mine way back & I routinely blast some Electronic Contact Cleaner into the air bypass to clean the hot wire & it's mate, but not while it is running of course.

As I understand it many MAFs put a "burn" voltage through the platinum wire for a few seconds on engine shutdown, but I seem to recall the Hitachi/Lucas MAF does not.

I'm sure someone will correct me if that is wrong, but assuming that it doesn't, the possibility of contamination of the wire is much greater especially in high dust enviroments.

Another idea I have seen, although it wasn't on a Discovery but was still an RV8, was a heat shield clamped to the clamps at each end of the MAF & reduced the amount of radiant heat getting to it from the exhaust manifold & possibly affecting it's correct operation.

Something like this but this is a TVR.

RV8 heat shield.

I have some stiff silver AC duct foil wired around my MAF but sitting away from the MAF leaving an inch air gap.

Does it make any difference? I don't know, but all these no cost things are worth a try I think.

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You may find this article will explain a lot.

Rover V8i

Hot Wire MAF sensors are very prone to sensing wire element contamination. A condition referred to by many technicians as “growing hairs” happens when debris, dirt from cheap air filters and outside air stick to the sensing wire element, shielding it from the incoming air. This shielding effect prevents the MAF sensor from correctly measuring the air flow and mass causing severe air-fuel ratio control problems. An ECM not in control while at pre-load is a strong indication of a dirty MAF.

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I mention and suggested the Raod Speed Transducer waaaaaaaaaaaaaay back in this thread,

this collects signal for the ECU and can affect t/o and from a crusising speed to staionary and other probs.

Have tread what you have done so far, but have you done anything to rule this out ?

Nige

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I mention and suggested the Raod Speed Transducer waaaaaaaaaaaaaay back in this thread,

this collects signal for the ECU and can affect t/o and from a crusising speed to staionary and other probs.

Have tread what you have done so far, but have you done anything to rule this out ?

Nige

Nige, I haven't ruled it out, but was figuring that since the speed gauge is working that the sensor must be working? Ordered a new coil and fuel temp sensor so will see how they work out before trying the VSS (same thing right?)

Thanks

Ben

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I'm pretty sure the problem is fixed.

I took a voltmeter reading of the MAF CO trim value with the intention of having a little trial and error with the setting. I made the mixture richer with half a turn of the screw and hey presto I can't get it do anything it shouldn't. Gave it about 40km testing fast/slow/stopping suddenly - all good.

Obviously still needs a little more testing and will probably get it tuned again through the main dealer, but for now it's looking good.

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Great result so far! This is why I mentioned having the probe put up the zorst so you can get an accurate idea of what is happening with the CO.

Now you know. Sort of. :rolleyes:

Having an Auto Elec or tuneup place shove a probe up the exhaust would tell you if the MAF is faulty. It may simply need adjusting, or like my 13 year old one had run out of adjustment & no matter what they did, they couldn't bring it back to specs.

It would pin it down & make your decision easier & more positive.

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No Diesels in Qatar!

I did have the Air Mass tuned just last week (by Bosch) but I guess the ECU is adaptive and I never drove it long enough with the new sensor on before getting it tuned?? Either that or they just didn't know the correct target setttings??

Also, I am wondering about the possibility of retro-fitting O2 sensors. I will run her "as is" for the time being and enjoy a little bit of reliabliity!

Thanks for everyones help.

:i-m_so_happy:

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