Sam Lever
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Hi Chaps and sorry for my second post being a p.i.t.a. technical one........
I spent a lot of last night reading posts on this forum in the hope of tracking down my problem, but think I am going to share it in all its glory here in the hope of some collective help & therapy!
My car is a '72 UK CSL. It is largely standard, though I do run Pertronix in the distributor and also an MSD ignition system, along with an MSD coil. Those mods were done literally years ago and made the car run much more cleanly, with better throttle response and great fuel economy. I run a set of Bosch Super 4 plugs that have been in the car for some time and I have not changed them recently. I do all of the mechanical work on the car myself and always have. I know pretty much where I've been and what I've done, but I am losing my way with this particular problem.
The car starts perfectly, hot or cold and runs for the most part very well. It has plenty of power and a decent top end (standard cam and valves/head). Idle is smooth and consistent, with no surging and it is running around 2% CO, which has been a bit of trial and error, but seems to make for the smoothest idle.
There are two very distinct issues with the running that are causing sleepless nights as I try to trace them:
Accelerate briskly up to, say 80 mph and than back off, as if to maintain that rather than slow down. The car will stutter and stumble, as if I had lifted right off and closed the throttle. Trying then to maintain 75 mph you can feel it stuttering. If you accelerate again it pulls cleanly through that and on to three figures very comfortably indeed, but the 60-80 mph is really tiresome.
Also, in built-up areas trying to maintain 30 mph in traffic involves a lot of very light throttle work and constantly coming off the light throttle and back on again. The car really stumbles on this and has occasionally cut out. Again, a tramp down on the throttle results in a very crisp pick up and it canters away fast. However, in traffic, that is neither possible nor legal and at 20-35 mph it is very uneasy.
This problem has been with me for a while, but has worsened over the past couple of years. So, what I have I done so far?
I suspected the Throttle Position Switch (TPS), so replaced that first a couple of years ago. It made no difference, new or old, just the same.
I have had a spare Manifold Pressure Sensor rebuilt at considerable expense in Germany and the symptoms are ideal to the old one.
I have replaced the ECU with a known used spare - again no change at all.
I have replaced the distributor speed points with a known used spare - no change at all
I have replaced the fuel filter, which was clean enough - no change at all.
I have replaced the main relay with a new one, as I suspected that this might have been cutting,/resonating and causing problems - no change
I wound the fuel pressure up to 32 psi. This did help with a high-speed pinking issue that I had also suffered, but made no difference to the issues noted above.
I have even run the distributor with the vacuum disconnected and plugged, working on the basis that there might be a momentary short or interruption as the plate was rotated within the distributor under varying load and vacuum, but no change.
My conclusion was that this was either related to manifold pressure or throttle position (or both), as these were the only variables that should be relevant in the circumstances where this problem occurs. Knowing that the MAP was now effectively rebuilt and should be beyond suspicion (plus the old one behaves just the same) I focused in on the TPS. I was troubled by the amount of play on the throttle drag-link shaft that drives the TPS and wondered whether under light throttle the top (driven) part of the TPS arm was being allowed to cant over and in some way break its contacts, producing erroneous readings. I separated top and bottom parts of the arm an inserted a washer as a spacer, so as to take up as much of the play between the two as I dared, removing the ability for the drag-link play to influence what was going on - no change.
I'm now running out of ideas as to what to do and what to check. I am thinking about plumbing in a fuel pressure gauge to where the cold-start injector goes and having that gauge in the cabin so that I can see what the pressure does when the symptoms occur. I kind of suspect that the pressure is momentarily dropping, but can't be sure. Either way I figure this will enable me to determine for sure whether this is an injection fault or ignition. If the pressure remains constant throughout then it would point to ignition perhaps, while if it flicks about then it confirms fueling issues?
Having been around the block with this more times than I care to think, I am also suspecting that it might be the wiring loom where it goes to the distributor contact points? This is one of the few legs that is allowed to move around as the engine rocks on its mountings and it could be that a hairline break has formed close to the plug and as I back off this is breaking momentarily????
Does it sound like I've begun to grasp at straws? I think so too!
I'd really appreciate some good ideas guys, as this is really getting me down. To put it into perspective, we went to the Le Mans Classic (4th one in this car) a couple of weeks ago and the trip was uneventful and fun. We cruised at between 80 and 90 all of the way and did about 24 mpg. The hesitation was always there, as per the symptoms above, but it never cut, never failed to start and was its usual joy to drive. This is just spoiling that party and I want to get it sorted.
I thank you all in advance - for reading this far and for any constructive help and guidance you can give to me.
With very best wishes from the UK,
Sam.
I spent a lot of last night reading posts on this forum in the hope of tracking down my problem, but think I am going to share it in all its glory here in the hope of some collective help & therapy!
My car is a '72 UK CSL. It is largely standard, though I do run Pertronix in the distributor and also an MSD ignition system, along with an MSD coil. Those mods were done literally years ago and made the car run much more cleanly, with better throttle response and great fuel economy. I run a set of Bosch Super 4 plugs that have been in the car for some time and I have not changed them recently. I do all of the mechanical work on the car myself and always have. I know pretty much where I've been and what I've done, but I am losing my way with this particular problem.
The car starts perfectly, hot or cold and runs for the most part very well. It has plenty of power and a decent top end (standard cam and valves/head). Idle is smooth and consistent, with no surging and it is running around 2% CO, which has been a bit of trial and error, but seems to make for the smoothest idle.
There are two very distinct issues with the running that are causing sleepless nights as I try to trace them:
Accelerate briskly up to, say 80 mph and than back off, as if to maintain that rather than slow down. The car will stutter and stumble, as if I had lifted right off and closed the throttle. Trying then to maintain 75 mph you can feel it stuttering. If you accelerate again it pulls cleanly through that and on to three figures very comfortably indeed, but the 60-80 mph is really tiresome.
Also, in built-up areas trying to maintain 30 mph in traffic involves a lot of very light throttle work and constantly coming off the light throttle and back on again. The car really stumbles on this and has occasionally cut out. Again, a tramp down on the throttle results in a very crisp pick up and it canters away fast. However, in traffic, that is neither possible nor legal and at 20-35 mph it is very uneasy.
This problem has been with me for a while, but has worsened over the past couple of years. So, what I have I done so far?
I suspected the Throttle Position Switch (TPS), so replaced that first a couple of years ago. It made no difference, new or old, just the same.
I have had a spare Manifold Pressure Sensor rebuilt at considerable expense in Germany and the symptoms are ideal to the old one.
I have replaced the ECU with a known used spare - again no change at all.
I have replaced the distributor speed points with a known used spare - no change at all
I have replaced the fuel filter, which was clean enough - no change at all.
I have replaced the main relay with a new one, as I suspected that this might have been cutting,/resonating and causing problems - no change
I wound the fuel pressure up to 32 psi. This did help with a high-speed pinking issue that I had also suffered, but made no difference to the issues noted above.
I have even run the distributor with the vacuum disconnected and plugged, working on the basis that there might be a momentary short or interruption as the plate was rotated within the distributor under varying load and vacuum, but no change.
My conclusion was that this was either related to manifold pressure or throttle position (or both), as these were the only variables that should be relevant in the circumstances where this problem occurs. Knowing that the MAP was now effectively rebuilt and should be beyond suspicion (plus the old one behaves just the same) I focused in on the TPS. I was troubled by the amount of play on the throttle drag-link shaft that drives the TPS and wondered whether under light throttle the top (driven) part of the TPS arm was being allowed to cant over and in some way break its contacts, producing erroneous readings. I separated top and bottom parts of the arm an inserted a washer as a spacer, so as to take up as much of the play between the two as I dared, removing the ability for the drag-link play to influence what was going on - no change.
I'm now running out of ideas as to what to do and what to check. I am thinking about plumbing in a fuel pressure gauge to where the cold-start injector goes and having that gauge in the cabin so that I can see what the pressure does when the symptoms occur. I kind of suspect that the pressure is momentarily dropping, but can't be sure. Either way I figure this will enable me to determine for sure whether this is an injection fault or ignition. If the pressure remains constant throughout then it would point to ignition perhaps, while if it flicks about then it confirms fueling issues?
Having been around the block with this more times than I care to think, I am also suspecting that it might be the wiring loom where it goes to the distributor contact points? This is one of the few legs that is allowed to move around as the engine rocks on its mountings and it could be that a hairline break has formed close to the plug and as I back off this is breaking momentarily????
Does it sound like I've begun to grasp at straws? I think so too!
I'd really appreciate some good ideas guys, as this is really getting me down. To put it into perspective, we went to the Le Mans Classic (4th one in this car) a couple of weeks ago and the trip was uneventful and fun. We cruised at between 80 and 90 all of the way and did about 24 mpg. The hesitation was always there, as per the symptoms above, but it never cut, never failed to start and was its usual joy to drive. This is just spoiling that party and I want to get it sorted.
I thank you all in advance - for reading this far and for any constructive help and guidance you can give to me.
With very best wishes from the UK,
Sam.