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The smooth silky idle has been replaced by a slightly more "sandpapery" version which sends a cyclic vibration through the car as the idle gently varies.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.

[TV8]

I would check all of the voltage settings on the AFM. If you have a volt meter, search for blitz on here and his website. Also, the fitting of the air intake pipe.

Does the stepper motor reset when you switch off? Short light rattle type noise.

Presumably, you have checked the fittings of spark plug leads/extenders? Has the routing of the leads changed during the service? When I was chasing a poor running problem, a mates old fashioned crypten tester showed an issue in how the leads were touching each other.

Your profile is Surrey/London. If you can get to mine, Hayes, I have a few bits and a Rover gauge connection you are welcome to try and borrow. Also, the south east TVR meeting is at the woodman pub ide hill lunch time todayThere is a guy there who has set up a mobile TVR service. I know he has helped a couple and is on here Paul Ukjd I think. Email me your number if you want to talk it through.

[ukdj]

Stuart,

as per Graham's post if you can make it today to :- The Woodman, Ide Hill, Goathurst Common, Sevenoaks TN14 6BU (12:00-15:30 ish)

I would be happy to take a look, if you can't make it, drop me a PM with your details and we can arrange something.

[jimed]

I assume the tickover was ok before your guy serviced it? In which case he should be a bit more proactive re whatever he has done. Can't really accept that it has just happened to go wrong just then, guess it could have but one big coincidence.
Is he a TVR specialist?
Jim

[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

[blitzracing]

Im assuming by the sounds of things the guy who serviced it has RoverGauge- its not ideal for detecting misfires as its an ECU diagnostic not ignition. Having said that you can see some very high levels of fuel trim as a misfire is mistaken for a lean mixture. The simplest way of picking up a misfire to to check the exhaust header temp by using a cable tie on the manifold where it leaves the exhaust port and see if it will melt. If you lost one cylinder it will be a lot cooler. Another thing you could try is drop all 8 plugs out and have a look at the colour, if one is not firing properly it will be a different colour to the rest. Not something silly like 2 plug leads swapped over?

[Steve_D]

Is there a modern equivalent to the old Crypton or Sun tester that killed the spark on each cylinder in succession to identify which cylinder(s) were not performing as well?

Steve

[N7GTX]

Your symptoms indicate a misfire under load i.e. low speed and low revs. This is when the spark needs to be at its best. If your 'specialist' has replaced the leads, plugs and distributor cap then that leaves the most common problem for misfires on the PH Chimaera section - the worse than useless plug extenders. During the service they will of course have been removed which may have pushed one or more over the edge or one or more may not have been refitted correctly.
Simply remove them and fit the plug lead directly on to the spark plugs as per a 'normal engine' and see if it improves. Many owners have now deleted these and fitted heat socks instead.
And your specialist should be sorting this, not you.

[swisstoni]

This exact symptom happened to my old Chim directly after a service and I never got to the bottom of it.
From the posts above, it really does sound like something was disturbed during servicing and the plugs / leads sound like prime suspects.

[Englishman]

I had similar symptoms on return from a service a couple of years ago. Was simply one of the plug leads just resting on an extender rather than being properly connected. Pluged it on, and everything back to normal.

[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.

[TV8]

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.

[tofts]

When the specialist adjusted the timing, it may have moved a tad, the 14mm bolt that holds the dizzy down is notoriously difficult to access!

I always set them to around 9deg. Anything else can cause symptoms as you describe.

[andy43]

I'm not an expert but the timing marks may not relate to the actual engine's position - mine didn't.
Plus I'd ask the specialist to reinstate all your old ignition bits as a lot of brand new rotors/plug extenders/dizzy caps are known to be generally crap quality and can cause more problems than they cure.

[portzi]

Firstly we need to establish is your mechanic a TVR specialist? If it's one of the renowned one's who are genuine ex factory mechanics like X-works or v track road etc , then l am very surprised they cannot sort your problem out. These cars are simple, but unfortunately have lots of TVR quirks that are tricky to find and ex factory knowledge is priceless that these specialists have gained over many years of working on them.

[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?

[TV8]

ToneyCaroney said:

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?

The instructions are shown here on Mark (blitzracing) who has also posted on this thread. His email address is on the website and he is a thoroughly helpful person. http://www.g33.co.uk/fuel_injection.htm

FYI, I am Hayes Kent, in between Croydon and Bromley, not the one out west!

[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.

[blitzracing]

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

[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.