V8 Question

[Disco95]

Hi guys, My 3.9 was doing the old rev up then die, rev up then die. I cleaned the stepper motor, cleaned the MAF and this improved the situation only slightly. Now it's two weeks or so later and she idles rough when cold, ol a little fast even, then when she warms up she pretty much doesn't want to idle at all. Under acceleration there's no starving, so I don't think there's a fuel pump issue.
I've ordered a new temp sensor which should arrive tomorrow or friday, but I can't seem to see where it's supposed to go:blush:
Can anyone please tell me, or is it the same one that operates the gauge?
Regards,
Sean.

[Tank]

Sean, did you remove the stepper motor from the back of the plenum to clean it? if so did you replace the gasket on the valve body, check there are no air leaks (vacuum) from hoses on stepper valve. I clean the MAF electrical connection pins by gently grasping then with needle nose pliers and pulling gently to remove any buildup, then I give them a slight twist, spray with contact cleaner, the plug as well, refit and remove the plug a few times, spray again with contact cleaner, refit and put 2 large plastic ties around MAF and plug.
I would also clean (or replace) the whole of the crankcase ventilation system, esp. the metal parts (T-pieces and so on) including the part on the rocker cover, drivers side.
If none of that helps it is time to check the electrical bits, go to an Auto Leccy and get them to test the coil and the Module on the dissy, you can check that the module has Heat Dissipating grease between the module and the dissy body, they get hot and need to dissipate the heat, you can get the thermo grease from any computer shop.
It doesn't sound like fuel as the problem seems to be at or near idle, so it could be temp. sender or even Throttle Pos. sensor, do you have a Thermostat fitted, if not it may not be reaching operating temp.
I would also clean all of the under bonnet electrical connectors with contact cleaner, incl. injector harness plugs.
It is extremely hard to diagnose a problem from afar, so I hope one of my suggestions works, call me if you wish, Regards Frank.

[Traco]

Check throttle position sensor is working properly and inlet manifold bolts are not loose. Also may be worth cleaning around the throttle butterfly.

[Disco95]

H guys, thanks for that Frank. I'd done most of those things, perhaps the gasket and vacuum hoses are worth a look. My sensor has not yet arrived. LV spares are usually quicker than this. Oh well, monday I guess. Anyway, it seems to be deteriorating, now I'm noticing rough running under gentle acceleration. (not that I do that too often:D)
It doesn't seem to want to accelerate at low revs, perhaps the worsening idle issue???
I'll play around and check and re-check a few things this weekend.
regards,
Sean.

[Tank]

Sean, if all the above check out it only leaves Fuel, maybe dirty/faulty injectors, try some good quality injector cleaner (suggestions anyone), next is fuel pressure regulator, take the small vacuum hose off the IAC valve(back of plenum), suck on hose if you get no vacuum or petrol in your gob, then that's the problem, from there it is the fuel filter and then the pump, good luck, Regards Frank.

[Pedro_The_Swift]

My Rossi did this twice,,
first was the stepper,
second was a split crankcase vent hose.

[Gooner]

Me (and my mechanic) tried Frank's suggestions from earlier threads also. Worked OK for a while - but eventually it was easier to just replace the damn MAF with a reco unit. I notice they are a lot cheaper on EBay these days...I paid $600 for a reco swap out.
Good luck with it.

[AussieAub]

Hey Sean,
I recently had a similar prob to what you're describing.
After much "diagnosis" I had been informed to replace the MAF, leads, plugs, and both CATS (after each item had been replaced seperately and the problem still existing after each), and it turned out to be the O2 sensors.

Just thought I'd mention it as no-one else has yet hinted at these.
My Disco runs much better.....for now!

Good look. Its as frustrating as hell, innit!

Cheers,

..:: KIEREN ::..
2000 Disco II Auto V8 (lemon edition)
AussieAubs Disco Page (http://aussieaub.blogspot.com/)

[Pedro_The_Swift]

My Rossi did this twice,,
first was the stepper,
second was a split crankcase vent hose.

When the MAF died it would only run properly on FULL go-pedal,,,



you can imagine how the fuel guage reacted to that:eek::angel:
luckily the tank was full--
and it was only 200 kays to home---
:twisted:

[Tank]

Me (and my mechanic) tried Frank's suggestions from earlier threads also. Worked OK for a while - but eventually it was easier to just replace the damn MAF with a reco unit. I notice they are a lot cheaper on EBay these days...I paid $600 for a reco swap out.
Good luck with it.
Gooner, what sort of improvement did you get by replacing the MAF, I was thinking of buying a new one and wondering if the expense is worth it, did you notice a difference, if so what improved, performance, fuel economy, idle, appreciate any feedback you may have, Regards Frank.

[4bee]

Imho, before you replace the MAF , it should really have an analyser probe stuck up the zorst to check for correct O2 settings. If it's faulty it should show up, & a slight adjustment may rectify it.

[Disco95]

Sean, if all the above check out it only leaves Fuel, maybe dirty/faulty injectors, try some good quality injector cleaner (suggestions anyone), next is fuel pressure regulator, take the small vacuum hose off the IAC valve(back of plenum), suck on hose if you get no vacuum or petrol in your gob, then that's the problem, from there it is the fuel filter and then the pump, good luck, Regards Frank.

Frank, I pulled the hose and sucked it, there was definately a vaccum there. Checked the CC ventilation bits. I've got a bit of oil around the area where it comes out of the rocker cover so maybe loosening and tightening it has improved the seal. Whatever the issue, she now idles smooth again. Still too many revs, but I recieved my new sensor today so changing that should solve that problem.
I went out for a little drive offroad yesterday, no problems there, ran like a dream even after the flogging the old girl got on the first hill climb. Didn't lock the centre properly and scrabbled up bouncing like a freaking rodeo horse at about 5000 RPM or so. Wheels smoking and engine roaring.
Scared the Crap out of Josie.

Anyway, thanks for all the suggestions guys. I'll take a pic of the sensor in question and where it belongs in the next couple of days.
Also snapped an engine mount, glad I have one of those sitting around. I knew it was going.

[Gooner]

Sorry Frank - I missed your reply and questions.

Immediately after my mechanic fitted the reco MAF I noticed it to be a fair bit smoother. There was never a problem with any missing or surging under load, just that damn idle drama that these V8s seem to get. Stalling at lights or in traffic aint good enough. Mechanic stuck a probe into my exhaust and said I was just about passing fuel straight out the back.
Idle is fine now - my mechanic went through all the stuff I gave him from the forum (including all your suggestions from previous posts) but it wasn't until he replaced the MAF that all was good again. Can't say I notice any change in fuel economy though.

Craig

[4bee]

If you didn't pull the plugs & clean them when the MAF was replaced, then you may want to do those as well.

After the MAF was replaced, I replaced the plugs (apx. $16 the set) as it couldn't be guaranteed that the carbon inside at the top of the electrode could be cleaned out or would burn out satisfactorily after running so rich for so long.
Seemed to be a noticeable improvement & it is still the same, so for the low cost, I'm glad I did.

[Pedro_The_Swift]

wow! $16!!!

a bit better than my $120 odd,,,,,
;)

[4bee]

I lied. it was more like $20.:D

But I know what you mean though. Some years ago I stupidly bought a set of eight from a Stealer here @ $9 each. Found them at K-mart for under $2. Back the $9 ones went back for a refund.

Good priced NGK plugs are around though.

The Stealer is not a Stealer any more, as they were one crowd that got dumped by L.

[AussieAub]

wow! $16!!!

a bit better than my $120 odd,,,,,
;)

Yeah, and mine!
I had quotes from $141 (Supercheap) to $215 (Repco)!!! :mad:


..:: KIEREN ::..
2000 Disco II Auto V8
Object Of Mass Consumption
AussieAubs Disco Page (http://aussieaub.blogspot.com)

[4bee]

I have just dug up the MC statement for the purchase of the plugs & something else from Sprint for a total of $62.90 but no invoice, but I suspect may have been a set of NGK plug leads. Plugs are NGK BPR5EY.

Imho, Repco are pricey for just about everything.

The closest I can get for now is a price from a Yank site @ USA$2.29 each which converts to AUD 25.40 for 8 off.

[Pedro_The_Swift]

Yeah, and mine!
I had quotes from $141 (Supercheap) to $215 (Repco)!!! :mad:


..:: KIEREN ::..
2000 Disco II Auto V8
Object Of Mass Consumption
AussieAubs Disco Page (http://aussieaub.blogspot.com)


yea,, but you ARE buying Platinum plugs,,,

[Disco95]

I have just dug up the MC statement for the purchase of the plugs & something else from Sprint for a total of $62.90 but no invoice, but I suspect may have been a set of NGK plug leads. Plugs are NGK BPR5EY.

Imho, Repco are pricey for just about everything.

The closest I can get for now is a price from a Yank site @ USA$2.29 each which converts to AUD 25.40 for 8 off.

Rip
Every
Poor
****
Off