Distributor Blues
Discussion
We (co-own the car with a friend) have a strange and annoying problem with the car, '89 350i.
Last week the car suddenly started misfiring like mad, managed to get it home but it would only pull above 2500 rpm and kept stalling. Checked the usual suspects and found the rotor arm was out of position and had far too much lateral movement. It turned out that one of the springs had come off the advance/retard mechanism, removing the distributor cap then allowed the rotor and mechanism to lift up completely out of position.
This was not a problem - take the dizzy apart, clean & reassemble.
Now the fun starts.
The car used to time up at 5 before TDC on the flywheel. Spent ages trying to get the car running again, checking the dizzy alignment at tdc etc.
It runs now but the timing is 10-15 degrees earlier on the flywheel than it used to be. I know that the flywheel marking can be way out but how can it change? We have double checked the re-assembly of the dizzy and it looks fine the mechanical advance appears to work OK though it is probably going to be a good idea to get some new springs if possible.
Anybody have any ideas?
Last week the car suddenly started misfiring like mad, managed to get it home but it would only pull above 2500 rpm and kept stalling. Checked the usual suspects and found the rotor arm was out of position and had far too much lateral movement. It turned out that one of the springs had come off the advance/retard mechanism, removing the distributor cap then allowed the rotor and mechanism to lift up completely out of position.
This was not a problem - take the dizzy apart, clean & reassemble.
Now the fun starts.
The car used to time up at 5 before TDC on the flywheel. Spent ages trying to get the car running again, checking the dizzy alignment at tdc etc.
It runs now but the timing is 10-15 degrees earlier on the flywheel than it used to be. I know that the flywheel marking can be way out but how can it change? We have double checked the re-assembly of the dizzy and it looks fine the mechanical advance appears to work OK though it is probably going to be a good idea to get some new springs if possible.
Anybody have any ideas?
That sounds pretty wierd. The work you've done inside the dizzy could obviously have affected the timing, but the timing you see on the crank pulley will always reflect what the engine is actually seeing regardless of what happens inside the dizzy.
It's possible the crank damper has shifted slightly so the timing marks on it are inaccurate. You could check this by finding the mechanical TDC yourself. Seems a strange coincidence that this would change exactly at the point you worked on the dizzy though.
The other possibility is that you are using an active timing light with an offset, and you have inadvertently changed the offset.
It's possible the crank damper has shifted slightly so the timing marks on it are inaccurate. You could check this by finding the mechanical TDC yourself. Seems a strange coincidence that this would change exactly at the point you worked on the dizzy though.
The other possibility is that you are using an active timing light with an offset, and you have inadvertently changed the offset.
I am glad somebody else thinks this is weird. We did not actually measure TDC position just turned the engine to the flywheel TDC mark on No.1 compression stroke, the piston looked close to the top so we assumed it was in position. I think finding the true TDC, as you suggested GreenV8S, is the next step.
We are starting to get a bit worried because we have booked the Snetterton track day on the 24th and still need to get a front brake upgrade bedded in first.
We are starting to get a bit worried because we have booked the Snetterton track day on the 24th and still need to get a front brake upgrade bedded in first.
Managed to get time off gardening duties to spend some time on the car this afternoon.
The timing light is just a basic inductive pickup type with no adjustment or offset features. A check of the TDC on No.1 shows the flywheel markings are pretty much spot on. If the timing markings on the flywheel are marked for +/- 10 degrees, there is a 10 mark but it is very faint, then the timing light is showing about 30-35 or more before TDC to get the engine to start and it will run down to about 10 but any touch of the throttle and it stalls.
I noted the position of the distributor body before it was taken off originally and the 30-35 I mentioned above matches with the amount (half because of the gearing) the dizzy has to be rotated anti-clockwise to get the engine to start. With the crank positioned at the firing point you can see that the rotor arm is pointing at no.1 contact on the cap and the lobe on the reluctor has just passed the center of the hall sensor.
Should an engine even run at 30 degrees advance?
The timing light is just a basic inductive pickup type with no adjustment or offset features. A check of the TDC on No.1 shows the flywheel markings are pretty much spot on. If the timing markings on the flywheel are marked for +/- 10 degrees, there is a 10 mark but it is very faint, then the timing light is showing about 30-35 or more before TDC to get the engine to start and it will run down to about 10 but any touch of the throttle and it stalls.
I noted the position of the distributor body before it was taken off originally and the 30-35 I mentioned above matches with the amount (half because of the gearing) the dizzy has to be rotated anti-clockwise to get the engine to start. With the crank positioned at the firing point you can see that the rotor arm is pointing at no.1 contact on the cap and the lobe on the reluctor has just passed the center of the hall sensor.
Should an engine even run at 30 degrees advance?
When I built the 4.5 I had the same problem with the dissy, it just would not sit right and not enough cclearence to even move the dissy to a position to get engine running correctly.
Took it out / in several times and eventually got it to a position where it would fit and turn for adjusting timing. It was a right bi**h and just got it started before the tuneup man came round to assist. I seem to remember the secret was to twist dissy as putting it in, get engine on TDC mark then put the leads on the dissy with the No 1 at the pont where the rotor arm was pointing
Good luck
Took it out / in several times and eventually got it to a position where it would fit and turn for adjusting timing. It was a right bi**h and just got it started before the tuneup man came round to assist. I seem to remember the secret was to twist dissy as putting it in, get engine on TDC mark then put the leads on the dissy with the No 1 at the pont where the rotor arm was pointing
Good luck
I can't get my head round the symptoms. You seem to have proved that the engine only runs with considerably more advance than it used to have. The only sense I can make is that either the advance you're measuring is not what you are actually getting, or the advance is compensating for some systematic fault in the ignition system.
If you take the dizzy cap off and turn the rotor arm, can you feel the mech advance moving and then springing back?
The dizzy has two advance mechanisms. The mech advance turns the input shaft relative to the drive gear. This affects the position of the pickup and the position of the HT contacts relative to the rotor arm, equally. I don't see how this could cause any trouble. However, the vac advance only moves the pickup relative to the input shaft. This means that the rotor arm moves relative to the HT contacts. Conceivably, if the vac advance was moved far enough then it could move the timing so far that the rotor arm didn't align with the HT contacts any moreand you might find the spark disappears or starts getting divided between multiple cylinders. I think you need to take the vac advance off and check it is hooked on to the adjustment mechanism properly. Also disconnect the vacuum line (and block off the port on the throttle body) just to make sure the vac advance isn't doing anything funny.
Can you get the problem to occur with the bonnet up? If so, connect a passive strobe and see if you can see any difference in the spark at the plugs when the problem occurs.
Also do the usual sanity checks, make sure the rotor arm is at the right height relative to the HT contacts, that the brush is still fitted in the dizzy cap, signs of tracking inside the dizzy cap etc.
All very wierd, if you manage to sort it I'd be interested to know what the problem was.
If you take the dizzy cap off and turn the rotor arm, can you feel the mech advance moving and then springing back?
The dizzy has two advance mechanisms. The mech advance turns the input shaft relative to the drive gear. This affects the position of the pickup and the position of the HT contacts relative to the rotor arm, equally. I don't see how this could cause any trouble. However, the vac advance only moves the pickup relative to the input shaft. This means that the rotor arm moves relative to the HT contacts. Conceivably, if the vac advance was moved far enough then it could move the timing so far that the rotor arm didn't align with the HT contacts any moreand you might find the spark disappears or starts getting divided between multiple cylinders. I think you need to take the vac advance off and check it is hooked on to the adjustment mechanism properly. Also disconnect the vacuum line (and block off the port on the throttle body) just to make sure the vac advance isn't doing anything funny.
Can you get the problem to occur with the bonnet up? If so, connect a passive strobe and see if you can see any difference in the spark at the plugs when the problem occurs.
Also do the usual sanity checks, make sure the rotor arm is at the right height relative to the HT contacts, that the brush is still fitted in the dizzy cap, signs of tracking inside the dizzy cap etc.
All very wierd, if you manage to sort it I'd be interested to know what the problem was.
Hi there, i am the counter part to Chris the other owner of the TVR. My names Mike, the car is located just up the A2 from you in Blackfen.
The problem is a real head ache, any assistance would be greatly appreciated. Both of us are getting a bit twitchy, looking forward to the track day at snett. But not the way the car is now!
Chris has covered all the bases in the previous postings, we are looking at sending of the dizzy for overhaul. But are not 100% convinced that the correct move.
The problem is a real head ache, any assistance would be greatly appreciated. Both of us are getting a bit twitchy, looking forward to the track day at snett. But not the way the car is now!
Chris has covered all the bases in the previous postings, we are looking at sending of the dizzy for overhaul. But are not 100% convinced that the correct move.
I could not get hold of a passive strobe but have borrowed another active one from the motor vehicle dept. at work.
The other thing we have had mentioned to us is the gap between the reluctor and Hall effect sensor, this should be 4 thou' apparently - unless anyone knows different?
I noticed in the EFI system pdf on the TVRWebPages that the ecu picks up the timing for the injectors from the distributor. The description says the injectors fire as two banks of four using four out of the eight reluctor lobes, how does the ecu know which lobes to use? Is there another crankshaft sensor somewhere?
The other thing we have had mentioned to us is the gap between the reluctor and Hall effect sensor, this should be 4 thou' apparently - unless anyone knows different?
I noticed in the EFI system pdf on the TVRWebPages that the ecu picks up the timing for the injectors from the distributor. The description says the injectors fire as two banks of four using four out of the eight reluctor lobes, how does the ecu know which lobes to use? Is there another crankshaft sensor somewhere?
Hall sensor could be to the source of the problem, as even with a not ok gap it function a lot better then what you experience. Friend of mine had hall sensor failure on his volvo. Remedy: replace dizzy complete, or install new/replacement hall sensor.
Can you try another dizzy (complete)? This trail and error could eliminate the dizzy completely. You could borrow mine (clutch gone and will take a while to fix it), but am in Belgium....
Find a complete dizzy (range rover efi, SD1 efi, etc.) Things to look out for: the drive shaft of the oil pump drive exists in two versions (slotted, or not slotted...). Amplifier type (get the same type as you have now). If tuned engine exchange the weights in the dizzy with the ones you have now to get the same advance.
Rob
Can you try another dizzy (complete)? This trail and error could eliminate the dizzy completely. You could borrow mine (clutch gone and will take a while to fix it), but am in Belgium....
Find a complete dizzy (range rover efi, SD1 efi, etc.) Things to look out for: the drive shaft of the oil pump drive exists in two versions (slotted, or not slotted...). Amplifier type (get the same type as you have now). If tuned engine exchange the weights in the dizzy with the ones you have now to get the same advance.
Rob
Hi there,
Following on from earlier episodes.
Was advised to check the air gap on the lugs to hall effect pick up, adjusted that up so the lugs just clear.
Now the car is starting ish, but while trying two different timing guns the timing mark can be seen to jump about. I still suspect the dissy, possible double triggering. We are tempted to get a new lucas 9EM amplifier and possible hall effect pick up. Does anyone have any theories.
Can anyone advise on any alternative dissy arangements ie MSD?
Following on from earlier episodes.
Was advised to check the air gap on the lugs to hall effect pick up, adjusted that up so the lugs just clear.
Now the car is starting ish, but while trying two different timing guns the timing mark can be seen to jump about. I still suspect the dissy, possible double triggering. We are tempted to get a new lucas 9EM amplifier and possible hall effect pick up. Does anyone have any theories.
Can anyone advise on any alternative dissy arangements ie MSD?
gibbema said:
Hi there,
Following on from earlier episodes.
Was advised to check the air gap on the lugs to hall effect pick up, adjusted that up so the lugs just clear.
Now the car is starting ish, but while trying two different timing guns the timing mark can be seen to jump about. I still suspect the dissy, possible double triggering. We are tempted to get a new lucas 9EM amplifier and possible hall effect pick up. Does anyone have any theories.
Can anyone advise on any alternative dissy arangements ie MSD?
YHM
Many thanks to FrenchTVR for coming over with his distributor and a spare ignition amp. Swapping the ignition amp did not fix the problem, swapping the whole dizzy did. It looks like the pickup was the culprit (which I kept calling a hall effect sensor but I think maybe is just inductive - only two wires).
We have been told that the replacement pickups that are available are often no use so it looks like we need to find another dizzy. Don't really want to spring for a new one or a Mallory, we are on the track of a second hand one so hopefully that will do the job.
Thank you for all of your suggestions and help.
We have been told that the replacement pickups that are available are often no use so it looks like we need to find another dizzy. Don't really want to spring for a new one or a Mallory, we are on the track of a second hand one so hopefully that will do the job.
Thank you for all of your suggestions and help.
There's a guy on Ebay who does replacement pickups with limited warranty: I got one last year and not only did it get the car running again (the old pickup had gone o/c), it also cured the mysterious 5300 rpm rev limit that I'd been blaming on my fuel injection work....!
Let me see if I can find him again...
ETA: Graham Dockree, docky57 on Ebay, that's the feller!
>> Edited by wedg1e on Thursday 13th April 17:30
Let me see if I can find him again...
ETA: Graham Dockree, docky57 on Ebay, that's the feller!
>> Edited by wedg1e on Thursday 13th April 17:30
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