Griffith 500 High Idle - Revs dropping very slowly
Discussion
Dear Pistonheaders.
The foolowing problem occured on a mates car and we cannot find a proper solution:
The car is a 1997 Griffith 500 and the idle, whether cold or warm will hold the revs around 2000rpm. Then slowly, really slowly drop to a 1100 rpm idle (was set up intentionally by using the bypass screw and blocked stepper bypass feed.). Main problem is that it does it when driving as well, which is annoying when you go low speed in a higher gear.
What we did is:
-clean the stepper and corresponding hole in plenum
-tested with a second stepper (brand new)
-searched for any air leaks
-checked any error codes (there aren´t any)
-resetted ECU
-tested with a secong AFM
After we disconnected the stepper at 1100 rpm the car was sweet as can be without any high idle with the revs dropping reasonably quick again when getting off the throttle. So we narrowed it to some wrong signal feeding the stepper.
Any ideas are highly appreciated. Perhaps anyone had a similar problem and could point us in the right direction.
All the best,
Björn.
The foolowing problem occured on a mates car and we cannot find a proper solution:
The car is a 1997 Griffith 500 and the idle, whether cold or warm will hold the revs around 2000rpm. Then slowly, really slowly drop to a 1100 rpm idle (was set up intentionally by using the bypass screw and blocked stepper bypass feed.). Main problem is that it does it when driving as well, which is annoying when you go low speed in a higher gear.
What we did is:
-clean the stepper and corresponding hole in plenum
-tested with a second stepper (brand new)
-searched for any air leaks
-checked any error codes (there aren´t any)
-resetted ECU
-tested with a secong AFM
After we disconnected the stepper at 1100 rpm the car was sweet as can be without any high idle with the revs dropping reasonably quick again when getting off the throttle. So we narrowed it to some wrong signal feeding the stepper.
Any ideas are highly appreciated. Perhaps anyone had a similar problem and could point us in the right direction.
All the best,
Björn.
Go to www.sc-power.co.uk they have a simple solution for that problem
Thanks chaps.
The stepper is sealed.
I was reading the thread and basically this is what we have done. But there was a time not too long ago when the Griff was fine with the stepper connected. So there must be something clearly causing the stepper to go mad.
And this leads me to the SC Power restrictor. I understand that this will drop the revs like blocking the feed for setting up the basic idle, but it should not be necessary on a good set up car with all sensors working, should it?
I did not want to write this in fear of leading in the wrong direction:
The cables of the speed transducer were...well they could look better. Speedo starts at 20 miles, before that showing no speed. It suddenly jumps in then. So if the ECU gets any interferences on PIN6, which feeds the ECU with the signal of the transducer telling it that the car is not stationary, could not this lead to a misbehaviour of the stepper? (Under normal conditions this would tell the stepper to rise the revs and hold them a little to avoid wheel lock while downshifting as far as I understand the system. Something the 370Z does reasonably better, but basically the same :-))
So question is:
Did someone experience the behaviour from a broken speedo transducer?
All the best,
Björn.
The stepper is sealed.
I was reading the thread and basically this is what we have done. But there was a time not too long ago when the Griff was fine with the stepper connected. So there must be something clearly causing the stepper to go mad.
And this leads me to the SC Power restrictor. I understand that this will drop the revs like blocking the feed for setting up the basic idle, but it should not be necessary on a good set up car with all sensors working, should it?
I did not want to write this in fear of leading in the wrong direction:
The cables of the speed transducer were...well they could look better. Speedo starts at 20 miles, before that showing no speed. It suddenly jumps in then. So if the ECU gets any interferences on PIN6, which feeds the ECU with the signal of the transducer telling it that the car is not stationary, could not this lead to a misbehaviour of the stepper? (Under normal conditions this would tell the stepper to rise the revs and hold them a little to avoid wheel lock while downshifting as far as I understand the system. Something the 370Z does reasonably better, but basically the same :-))
So question is:
Did someone experience the behaviour from a broken speedo transducer?
All the best,
Björn.
http://www.rv8r.co.uk/tickover.html
Bjorn. For a full Stepper service thread. I have yet to do this. On mine I have cleaned the nose, shaft and spring of the stepper and also the housing in the rear of the plenum including the side hole from housing into the plenum. (its unseen because of the sight angle but can be felt with finger) I have also treated the shaft insert with a drop of electrical cleaner lubricant (Ambersil super 10 or similar)Also the stepper connections. Dont overtighten the stepper it can crack the rear of the plenum.
By speedo transducer, do you mean the sensor on the toothed wheel on the axle drive shaft. Just replaced mine since speedo went caput after erratic jumping. Now fixed.
Bjorn. For a full Stepper service thread. I have yet to do this. On mine I have cleaned the nose, shaft and spring of the stepper and also the housing in the rear of the plenum including the side hole from housing into the plenum. (its unseen because of the sight angle but can be felt with finger) I have also treated the shaft insert with a drop of electrical cleaner lubricant (Ambersil super 10 or similar)Also the stepper connections. Dont overtighten the stepper it can crack the rear of the plenum.
By speedo transducer, do you mean the sensor on the toothed wheel on the axle drive shaft. Just replaced mine since speedo went caput after erratic jumping. Now fixed.
Edited by EGB on Monday 21st November 10:04
You need to monitor the road speed signal as it goes into the ECU. With the car stationary it should be 0 volts, but with the car moving above 3mph you get a fixed frequency pulsed signal. If the signal is present when the car is stationary the idle will remain high, or simply be unstable. The signal is generated by a "Speedo recalibration box" that is under the dash (on the Chims anyway) that picks up the cars moving from toothed wheel and sensor(I think its near the diff) and then produces a fixed string of pulses to tell the ECU the car is moving. Its a pretty poor bit of design as if the inputs of the unit get poor earths or electrical noise it gives a false signal when the car is stationary.
Pin outs here.
http://www.britishv8.org/Articles/Rover-14CUX-EFI....
Also check any posts by "MikeTVR"
Pin outs here.
http://www.britishv8.org/Articles/Rover-14CUX-EFI....
Also check any posts by "MikeTVR"
Edited by blitzracing on Monday 21st November 13:17
This is a good hint.
Speedo transducer at the diff was changed but made no difference in the Griff´s behaviour.
Time to start looking for "the box". Any idea or a picture for location purposes?
All the best,
Björn.
P.S.: I hasten to add that any mechanical failure like sticking throttle cable or not closing plate was ruled out way earlier. When the stepper is removed all is fine. It will definately turn out to be some electrical gremlin.
Speedo transducer at the diff was changed but made no difference in the Griff´s behaviour.
Time to start looking for "the box". Any idea or a picture for location purposes?
All the best,
Björn.
P.S.: I hasten to add that any mechanical failure like sticking throttle cable or not closing plate was ruled out way earlier. When the stepper is removed all is fine. It will definately turn out to be some electrical gremlin.
Good read on britsihV8.org.
This brought up another potential source of the problem. What if the coolant temperature sensor gives wrong reading to the ECU and thus lengthening the opening interval of the injectors? Stepper is opened since lambda detects unburnt fuel > high idle. It seems as if it runs a bit rich as well to be honest.
Björn.
This brought up another potential source of the problem. What if the coolant temperature sensor gives wrong reading to the ECU and thus lengthening the opening interval of the injectors? Stepper is opened since lambda detects unburnt fuel > high idle. It seems as if it runs a bit rich as well to be honest.
Björn.
The "speedo recallibration box" is under the dash (on the Chims anyway) and about the size of a packets of fags. Ive not pull a Griff dash to bits however. As for the running a bit rich, this is the more important bit to get right, or you will never get a good idle. The lambdas should be switching at idle, if they are stuck at around 1.2 volts the ECU has lost control of the mixture. I have seen some TVRs just stop the switching at idle and still run perfecly well as the RPM rises. You can test to see if the lambdas are working by letting in a bit of air by part removing one of the screw bungs in the plenum, and see if they start to switch.
The stepper motor operation is actually quite involved. I've been final testing a new diagnostic unit I'm developing that gets data direct from the ECU on a real time basis so it will display the stepper motor position, throttle pot, water and fuel temperatures, road speed, lambda status, AFM operation, etc etc as well fetch and clear any fault codes without having to disconnect the battery. It also enables you to override the ECU and move the stepper motor directly as well as switch the fuel pump on or off.
What has been surprising is that the stepper motor is affected by several factors. The ECU receives load information if the car is put into drive (TVR assert this signal permannently BTW) or if the A/C is switched on. The stepper motor immediately adjusts to increase the revs. The movement is small but the kit detects it. The stepper is reset when the ECU is switched on but if there is a fault with the coolant temperature, it doesn't and the unit stays where it is. Again this is something that the unit shows and may explain the frequent cases of failed stepper motors that actually haven't. Fortunately, the unit allows me to activate the stepper so I could check that the lack of movement was not caused by a problem. This siituation could leave the stepper in the totally wrong condition and hence the problem with a slow idle. The stepper gives no feedback to the ECU so that it assumes that it is in the reset position when it isn't. Normal operation may as a result be very strange. No fault with the system except that the stepper is not in the right place.
The road speed sensor is very important as it controls when the ECU enters an idle mode. The ECU normally assumes a ramped signal but TVR give it an all or nothing type of signal which is not what is normally expected. The ECU thinks the car is going from 30-40 mph to 0 instantly and again, some pretty strange things happen. As a result I am looking at a simple replacement for the TVR box that profiles the signal correctly so that the ECU sees more what is expected rather than the shock that TVR provide. I suspect that this is also making things worse.
Equally any noise on the input is enough to confuse the ECU as well. I could generate sufficient noise with a bare wire to fool the ECU into thinking the car was still moving.
I think that this does indicate why many have failed to get to grips with the problem as it looks like there are multiple areas which can affect the idle and it is very difficult without this kit to see what exactly is going on.
What has been surprising is that the stepper motor is affected by several factors. The ECU receives load information if the car is put into drive (TVR assert this signal permannently BTW) or if the A/C is switched on. The stepper motor immediately adjusts to increase the revs. The movement is small but the kit detects it. The stepper is reset when the ECU is switched on but if there is a fault with the coolant temperature, it doesn't and the unit stays where it is. Again this is something that the unit shows and may explain the frequent cases of failed stepper motors that actually haven't. Fortunately, the unit allows me to activate the stepper so I could check that the lack of movement was not caused by a problem. This siituation could leave the stepper in the totally wrong condition and hence the problem with a slow idle. The stepper gives no feedback to the ECU so that it assumes that it is in the reset position when it isn't. Normal operation may as a result be very strange. No fault with the system except that the stepper is not in the right place.
The road speed sensor is very important as it controls when the ECU enters an idle mode. The ECU normally assumes a ramped signal but TVR give it an all or nothing type of signal which is not what is normally expected. The ECU thinks the car is going from 30-40 mph to 0 instantly and again, some pretty strange things happen. As a result I am looking at a simple replacement for the TVR box that profiles the signal correctly so that the ECU sees more what is expected rather than the shock that TVR provide. I suspect that this is also making things worse.
Equally any noise on the input is enough to confuse the ECU as well. I could generate sufficient noise with a bare wire to fool the ECU into thinking the car was still moving.
I think that this does indicate why many have failed to get to grips with the problem as it looks like there are multiple areas which can affect the idle and it is very difficult without this kit to see what exactly is going on.
Sounds similar to my problem, which still isn't resolved. Have a look here for a couple of vids - http://www.pistonheads.com/gassing/topic.asp?h=0&a...
Sounds like the Throttle Control is back to be favourite as the culprit. Would be interested in acting as a guinea-pig for Steve's new box of tricks :-)
Sounds like the Throttle Control is back to be favourite as the culprit. Would be interested in acting as a guinea-pig for Steve's new box of tricks :-)
I dont understand why TVR put in the speed conversion box with the fixed frequency signal in the first place unless it was prevent the ECU from limiting the top speed as it does on the 4x4 fuel map. This paramenter can be turned off in the chip anyway so you could feed the ECU with the correct speed signal.
Mine used to have this exact problem until i rebuilt the engine, now its fine. The re build only involved changing mechanical things and cleaning. Nothing electrical or sensor wise was touched. I am convinced it was an air leak somewhere around the plenum.
If i were you i would take the plenum off including the base from the manifold. Give everything a good clean including throttle bye pass, mine was made up with all sorts of crap. Also clean the other side of the stepper motor which you cant get to from the exterior. Then replace base and top using a liquid gasket to negate all possible air leaks.
It is not a big job and wont take long. At least then you can be 100% sure re air leaks. As said the only thing i have done which i can relate to curing this problem is thoroughly clean plenum and intake and properly seal it all.
ETA make sure tube from fuel regulator to plenum is good.
If i were you i would take the plenum off including the base from the manifold. Give everything a good clean including throttle bye pass, mine was made up with all sorts of crap. Also clean the other side of the stepper motor which you cant get to from the exterior. Then replace base and top using a liquid gasket to negate all possible air leaks.
It is not a big job and wont take long. At least then you can be 100% sure re air leaks. As said the only thing i have done which i can relate to curing this problem is thoroughly clean plenum and intake and properly seal it all.
ETA make sure tube from fuel regulator to plenum is good.
shpub said:
The road speed sensor is very important as it controls when the ECU enters an idle mode. The ECU normally assumes a ramped signal but TVR give it an all or nothing type of signal which is not what is normally expected. The ECU thinks the car is going from 30-40 mph to 0 instantly and again, some pretty strange things happen. As a result I am looking at a simple replacement for the TVR box that profiles the signal correctly so that the ECU sees more what is expected rather than the shock that TVR provide. I suspect that this is also making things worse.
Fascinating stuff Steve. I wonder if this behavior with the speed sensor is contributing to the shunting that many people experience. It kicks in at about 3mph when its working, so below that stepper control should function as normal. I could well think that if say it was switching at 20 mph it would shunt horribly as the stepper control was switched between running mode and idle mode. I dont see a situation of it causing an over low idle what ever the signal is doing, as with the signal present the idle is lifted, and without it it should return to its programmed idle setting of say 800 rpm.
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