RV8 14CUX Idle air valve

[100SRV]

Hi,
the idle air valve (stepper motor) on my 3.9 V8 is becoming lazy so I thought I'd pre-empt it's demise by buying a replacement. Before I do this have any of you had success with the cleaning process described on the g33 website?

The reason I suspect a lazy IAV is that it holds the engine speed very high after start up (about five or so seconds although I've not timed it accurately)

I've read of cheap copies which don't work correctly (g33 website) and also found that there are two part numbers for the same type of part:


ETC6660 3.5, 3.9, 4.2 Litre up to 1995 Except SD1
ERR5199 3.9 Litre 1995 on

Is there any functional difference between them or just change in supplier?

100SRV

[Steve_D]

RoverGauge should show you if the stepper is working properly.
Watch it from startup and check that it is moving and slowly bringing the revs down. later when it is warm switch on all the electrical load you can find and watch RoverGauge to see if the stepper opens to keep the revs up.
If this is all working then the stepper is OK.

Having said that they always benefit from a clean.

Steve

[100SRV]

Hi Steve,
I'll have to install Rovergauge on the laptop - I have the basic 7-segment LED code reader with USB port but never got around to the software bit.

Thank you.

Any ideas on the wet plugs fault in my other post?

100SRV

[andyiley]

If i tseems to be running on 4 common logis says the reverse of your original thinking is true.

4 wet plugs - no spark

4 dry plugs - firing correctly

So, although I won't rule out one bank of injectors not operating, I would be more inclined to believe the other bank of plugs aren't sparking.

[100SRV]

andyiley said:

If i tseems to be running on 4 common logis says the reverse of your original thinking is true.

4 wet plugs - no spark

4 dry plugs - firing correctly

So, although I won't rule out one bank of injectors not operating, I would be more inclined to believe the other bank of plugs aren't sparking.

Good thinking Andy!
The engine has a conventional distributor / lumenition / coil
But still not sure how that would account for the bank of four on the same side all being wet?

ETA:
As the coil was the last thing I tinkered with I will start there, I did get odd symptoms of a damp distributor a while ago and upon inspecting the coil found that the HT insulating nose had cracks so I fitted my onboard spare.

Later I'll fit the one I took off to see what happens but I'm going to buy a new coil because I no longer have a spare and am not sure whether the (previous spare) coil is a good 'un.

I checked the resistance of the two injector banks - both close at 4.4 / 4.6 ohms.
Tune resistor was present at 470 Ohms

Edited by 100SRV on Thursday 5th March 16:06

[100SRV]

Update...

I tried the "old" coil and "new" coils both gavet the same symptoms of starting/initial running on just four cylinders.

I suppose that eliminates the coil as the culprit, I'll have a closer look at the distributor cap in daylight tomorrow.

[andyiley]

It also might be worth a good check of the HT lead runs, just in case a bit of ham-fisted work has pulled the 4 to the wet side partially out, or if they all run over something that has damaged them.

It could even be that those 4 are the longer runs & the leads are a bit old/worn/damaged, or even the plug condition/gaps on that side.

Can you pull the plugs and check for sparks?

[100SRV]

andyiley said:

It also might be worth a good check of the HT lead runs, just in case a bit of ham-fisted work has pulled the 4 to the wet side partially out, or if they all run over something that has damaged them.

It could even be that those 4 are the longer runs & the leads are a bit old/worn/damaged, or even the plug condition/gaps on that side.

Can you pull the plugs and check for sparks?

No change in the HT lead runs, they are grouped with the plastic clips so they don't touch the engine or each other, 5 and 7 are crossed over during the length too. The leads are two year's old and mate snugly to distributor cap and sparking plugs. I'll pull them all off and give them a close inspection and clean in the morning.

The plugs all had similar colour once the wet ones had dried off, I'll check the gaps in the morning while the HT leads are off.

Why would this only happen at start up? The engine pulls well at WOT with no trace of hesitation or misfiring.

[Steve_D]

Something to think on.
On TVRs with the RV8 the coil lives on a bracket hung of the front offside plenum bolt.
A fault we have seen more than once is the earth wire for the front injector chaffing on the coil bracket and shorting.
Result... all the injectors on that bank are fully open so wet plugs and misfire due to too much fuel.

Again this may go away as the engine warms and something expands curing the short.

Steve

[100SRV]

Hi Steve D,
Good suggestion, thank you.
The coil is mounted on LH inner wing (Bowler Tomcat).


I got up early and:
removed, cleaned and checked all HT leads - 0 defects and connectors fit snugly at both ends.
removed, cleaned and checked all sparking plugs - 0 defects and gap of 0.9mm +/- 0.01mm
checked injector wiring - all safe inside either PVC sleeve or split conduit

I haven't started it yet to see whether I've scared the gremlin away.

100SRV

Edited by 100SRV on Friday 6th March 08:47

[100SRV]

Over the weekend I replaced the fuel injectors with a known good spare set I have. These are better described as an excellent set because when tested there was < 3% deviation in flow rate across the set!

The rich right-bank problem hasn't returned yet and I'm inclined to think it was a lean left bank rather than over rich.

I have just fitted a new idle air valve and now the significant start up engine speed flare has gone and idle management between gears and at junctions is how it should be.

Thank you for the suggestions...

100SRV