Shunting / rough running after service

[ToneyCaroney]

Hi All,

My Griff 500 returned from a recent 6k service at my usual specialist with a rough running issue. the issue manifests itself in the folllowing ways:
Noticably rough running at low throttle openings at low revs. It feels a bit like a frequent mild hiccup or mild misfire.
The engine sounds slightly odd (can't quite put my finger on it) and feels less smooth during hard acceleration.
The smooth silky idle has been replaced by a slightly more "sandpapery" version which sends a cyclic vibration through the car as the idle gently varies. It just isn't quite right.

I've also noticed that the exhaust note has changed. It sounds more flatulent(!). At a cruise it sounds as though the gases are rhythmically popping out of the pipes rather than the gentle "wuffle" of before.

I should point out that it has always run beautifully smoothly before (I've had it 3 years) with none of these traits. The cam shaft was changed earlier this year but again, the car was running beautifully after that. I've been back to my specialist who has spent time on it including replacing leads and plugs as well as swapping the distributor with the same results. He has also run it through diagnostic software that indicates that everything (Lamdas etc) are running correctly. The specialist thinks the ignition timing may be the issue but it doesn't like the factory settings (car is standard) and attempts to manually set it do not seem to have improved matters.

Unfortunately, the specialist has now said that he cannot improve it any further and so I need some advice as to what it could be and who to get to look at it. Compared to how it used to be it's running rather poorly. Something clearly isn't right!

Cheers.

[ToneyCaroney]

Thanks gents.

TV8, I can't hear any rattle type noise when the engine is switched off.
I checked the leads and extenders before returning it after the service. All were OK. Since then, the specialist has replaced all leads, plugs etc and swapped the dizzy and the issue remains although I haven't re checked everything since.

Thanks for the offer re the bits and rover gauge. Really very kind. Not sure how to use it but maybe I'll give you pm later.

Ukdj thanks also for the kind offer. Unfortunately I can't make it today but perhaps I'll drop you a pm this week

[ToneyCaroney]

Thanks all. I checked the leads, plugs and extenders before I took it back for it to be investigated. Subsequently the specialist changed the leads plugs and extenders again (along with swapping out the dizzy) and the issue persists and so, unfortunately, I don't think it is quite as straight forward. The specialist seems to think it is ignition timing related. Apparently it doesn't like the factory ignition settings and wasn't set to them when it went in for service. I think it is possible that they have been changed and now they can't get them back to where the car likes it. Maybe I need someone 'old school' to take a look???

Blitz, thank for the info. I don't know whether they were using the Rovergauge software or something else. I'll test the manifold theory when I next get a chance.

Jimed, you are right of course but I don't think they are going to get it back to where it was and so I would rather just get on with trying to get it sorted myself.

[ToneyCaroney]

TV8 said:

Hi OP, your stepper motor should do a little whirr when you switch off the engine, also have you checked the AFM voltages? The AFM can cause a few problems - is it a genuine lucas one? please see http://www.pistonheads.com/gassing/topic.asp?h=0&a...

My problem started when I changed exhaust but it was just a coincidence. I have spare lucas original that you are welcome to borrow if required.

Thanks again TV8. Unfortunately I'll be away from the car until later this week so can't check anything out until then. I'll certainly let you know. I don't remember the stepper making any noise when switching off and I did have a listen yesterday. How do I measure the AFM voltage?

[ToneyCaroney]

Update.

So I've checked a few things today and can report the following:

The stepper motor does rattle when I switch the ignition off.
The AFM voltages behave as follows: immediately jumps to 0.6 volts on switching on ignition and then settles to around .33 volts after around 20 seconds.
With the engine running the voltage is 1.58. I don't think this is correct for a 500? Both tests taken when the engine is warm.

I have also checked the leads and extenders and all looks well. Both the leads and extenders are new.

For completeness,in addition to the 6k service, my specialist has also undertaken the following in troubleshooting this:

Replaced ignition amp
Replaced ignition coil
Replaced ht leads and cap ends
Replaced distributor cap and rotor arm
Updated fuel and ignition relays and tried another ECU in car.

Repeated entire process.

Cheers.

[ToneyCaroney]

blitzracing said:

The initial spike should be done and dusted very quickly (less than 1 second) the response you have is typical for a failing unit.

This is a plot for a 3.9 on start up- so the idle is 1.62 volts. A 500 is 1.75v

Thanks blitz, very useful. Could this explain why the car was running very rough on the factory ignition timing settings? Is it feasible that the specialist may have been able to partially compensate for the failing afm by manually adjusting the timing to get smoother running?

Thanks.

[ToneyCaroney]

Thanks Al, seems sensible but my thinking is that if the timing is altered to compensate for a dodgy afm the replacing it with a good one won't tell me anything unless I can adjust the timing to match. I can probably wield a spanner enough to swap out an afm but ignition timing is beyond my powers!
Cheers, Stu

[ToneyCaroney]

Ok, so ran the car without the extenders today and no better unfortunately. Looks like the afm is still the favourite though but still not sure about the timing thing. Anybody know if the non standard ignition timing might be to compensate for a dodgy afm? If so, presumably I will need to alter the timing when a good afm is fitted?

Cheers.