Hi all,
I have a 1967 VW Camper with a Megajolt Lite fitted. The engine is 1955cc with twin 40 Webers, Porsche cooling, 1.25 ratio rockers, Engel 120 cam, external oil cooler and filter. I've mapped the ignition and it runs fine and will shortly be taking a trip to the rolling road. There is the occasional backfire when the engine is cut, usually when the engine is hot.
The problem I have is cold starting. If the van hasn't been used for a week or so and the temps have been very cold, she's a pig to start. I want to use the auxiliary input channel to adjust the timing to help cold starting. I've bought a GM engine temp sensor and fitted it into the external oil line to the filter. I want to use the oil temperature when cold to trigger the advance correction table but am a little unclear as how to do this. I can't find anything re calibration of the temp sensor but if I tell you my method, can someone correct me if I'm wrong :-
The sensor output varies between 0v and 5v.
The auxiliary input channel (aic) has a range of 255 values and this can be matched to the output from the sensor giving an increment of approx .02v per step.
First, I put the sensor in ice and measure the corresponding voltage output, say 1.04v. This would correspond with line 52 on the aic (1.04 divided by .02).
I then repeat the exercise with the sensor in boiling water and again record the output voltage, say 3.4v. This would correspond with line 170 on the aic (3.4 divided by .02).
I then use an excel spread sheet to extrapolate the rest of the values to complete the 255 lines. This is then imported into the Megajolt.
I can now edit the 10 advance correction bins to adjust the timing depending upon the temp of the oli and hence engine.
Is this correct?
The temperature range recorded by the sensor is a lot greater than I actually need in that I only need to use a range of maybe -10c to 100c. Can I adjust bins to give me this narrower range ie just use from line 44 to 170, which would give me that approx. range?
Thanks for your help in advance.
Paul
Cold Start Set Up - In Simple Terms Please
Moderators: JeffC, rdoherty, stieg, brentp
Cold Start Set Up - In Simple Terms Please
The more stupid questions I ask, the smarter I get!
Hi Paul,
Just some questions that come up:
Have you tried increasing cranking advance to see if further advance does make a difference? You could in addition add MAP nr.2 with extra advance at low revs.
Did this problem start after you converted to MJ?
Did your previous ignition operate with a similar spark voltage or was it higher?
When you make your starting attempts, is there fuel in the float bowls or does that need to be pumped up first?
What type of carbs do you use?
Sorry, can't answer your question in simple terms
but your issues are interesting; I am experiencing similar problems when I try to start up my test engine after it has been idle for some weeks in sub-zero temperatures.
Alex
Just some questions that come up:
Have you tried increasing cranking advance to see if further advance does make a difference? You could in addition add MAP nr.2 with extra advance at low revs.
Did this problem start after you converted to MJ?
Did your previous ignition operate with a similar spark voltage or was it higher?
When you make your starting attempts, is there fuel in the float bowls or does that need to be pumped up first?
What type of carbs do you use?
Sorry, can't answer your question in simple terms
but your issues are interesting; I am experiencing similar problems when I try to start up my test engine after it has been idle for some weeks in sub-zero temperatures.Alex
Hi Alex,
I think you might be on the right line there. I spent last night reading up a bit more to refresh my memory as I'm new to all this. I think the basic mapping is ok to get the engine running but needs some fine tuning.
The engine is a brand new build running twin 40 Webers and apart from a 60 mile run back home from the restorers, has only done a few short trips around the local lanes because I've been trying to sort out a steering problem - it ran like a drunken supermarket trolley! Now that's sorted I am concentrating on the engine.
The engine was run up in the workshop on a distributor and the carbs balanced before we switched to the MJ. With hindsight, I should have run it on the dizzy for a few weeks before making the change - you live and learn.
There is fuel in the bowls and normally the engine starts on first crank. In the colder weather now it is a lot more reluctant to fire. I'm also getting some spit back through the carbs on cranking. According to my book, too little advance means the mixture doesn't get fully burnt and travels back into the manifold when the inlet valve opens so I think you're right. I'm also running an AFR gauge so I can keep an eye on the mixture and it's running around 14.4 which I think is probably a bit too weak. This lean mixture = longer burn time = more advance needed, so it may be fuelling rather than timing or a mixture of both.
I think I may be getting ahead of myself re cold start adjustment, and looking too far ahead rather than concentrating on the basics and getting them right. I think I'll book the van in for the session on the rolling road and hopefully get the basic mapping/fuelling correct before I consider cold starting.
I will add a few extra degrees to the cranking advance to see if that helps things before I do so. I'll let you know how I get on.
Thanks
Here's a pic of the engine :-
I think you might be on the right line there. I spent last night reading up a bit more to refresh my memory as I'm new to all this. I think the basic mapping is ok to get the engine running but needs some fine tuning.
The engine is a brand new build running twin 40 Webers and apart from a 60 mile run back home from the restorers, has only done a few short trips around the local lanes because I've been trying to sort out a steering problem - it ran like a drunken supermarket trolley! Now that's sorted I am concentrating on the engine.
The engine was run up in the workshop on a distributor and the carbs balanced before we switched to the MJ. With hindsight, I should have run it on the dizzy for a few weeks before making the change - you live and learn.
There is fuel in the bowls and normally the engine starts on first crank. In the colder weather now it is a lot more reluctant to fire. I'm also getting some spit back through the carbs on cranking. According to my book, too little advance means the mixture doesn't get fully burnt and travels back into the manifold when the inlet valve opens so I think you're right. I'm also running an AFR gauge so I can keep an eye on the mixture and it's running around 14.4 which I think is probably a bit too weak. This lean mixture = longer burn time = more advance needed, so it may be fuelling rather than timing or a mixture of both.
I think I may be getting ahead of myself re cold start adjustment, and looking too far ahead rather than concentrating on the basics and getting them right. I think I'll book the van in for the session on the rolling road and hopefully get the basic mapping/fuelling correct before I consider cold starting.
I will add a few extra degrees to the cranking advance to see if that helps things before I do so. I'll let you know how I get on.
Thanks
Here's a pic of the engine :-
The more stupid questions I ask, the smarter I get!
Hello Paul,
Have you tried to reproduce the advance the distributor was having before. This is what I've done on my project, I knew how much advance I had at idle, this is what I've done also for the MJLJ map. It started easily this way.
For now, every column in my map is having the same value to get rid of MAP/TPS input for the first runs.
Good luck!
Have you tried to reproduce the advance the distributor was having before. This is what I've done on my project, I knew how much advance I had at idle, this is what I've done also for the MJLJ map. It started easily this way.
For now, every column in my map is having the same value to get rid of MAP/TPS input for the first runs.
Good luck!
Mathieu
Hi Paul,
Cool looking engine compartment. By the look of it you are running either IDF or IDA carbs. Do they have the cold start enrichment device installed? If they have, does it also increase cold idling speed as on a carb that does have choke valves and a link between the choke cable and the throttle valve? If the answers are no then you can advance ignition 'till you are blue in the face, but a mixture that is too weak won't ignite. Moreover, with too much advance ignition will stop the engine fram cranking dead on its tracks when it fires, giving the suggestion the battery is going down because the engine won't crank nicely.
Alex
Cool looking engine compartment. By the look of it you are running either IDF or IDA carbs. Do they have the cold start enrichment device installed? If they have, does it also increase cold idling speed as on a carb that does have choke valves and a link between the choke cable and the throttle valve? If the answers are no then you can advance ignition 'till you are blue in the face, but a mixture that is too weak won't ignite. Moreover, with too much advance ignition will stop the engine fram cranking dead on its tracks when it fires, giving the suggestion the battery is going down because the engine won't crank nicely.
Alex
Cold Start Set Up - In Simple Terms Please
Hi,
Many thanks for the input from you all and thought I'd give you an update.
Booked the van in for a session on a rolling road to make sure I had the correct set-up. Chose this company which is reasonably local to me - 50 miles or so away :-
http://www.ahs-motorsport.co.uk/
After a quick 3 minutes on the rolling road and an explanation of the starting problem from me, Alan the boss ruled out any problems with the mapping as he couldn't hear any pinking, detonation etc. and concentrated on the carbs.
They were stripped and blown out with compressed air and he reset the float valve heights. He then found some play in the CSP throttle linkage which was causing one side to open quicker than the other creating an imbalance. This was corrected as best as he could but will be replaced with a dual cable assembly as soon as I can find one. The pedal assembly upfront was worn and needs replacing too as this was preventing full throttle being achieved. We then did another run on the dyno and this simple carb work had given us another 16 bhp!
Alan said it was not worth spending and more time (and money) until the new parts were fitted and we finished for the day. He also recommended fitting the cold start mechanism so that's another few parts added to my list.
The van ran so much better on the way home and started first time on the key this morning despite some low temperatures overnight. I'll post another update after the parts are fitted and I've had another session on the rolling road.
Many thanks for the input from you all and thought I'd give you an update.
Booked the van in for a session on a rolling road to make sure I had the correct set-up. Chose this company which is reasonably local to me - 50 miles or so away :-
http://www.ahs-motorsport.co.uk/
After a quick 3 minutes on the rolling road and an explanation of the starting problem from me, Alan the boss ruled out any problems with the mapping as he couldn't hear any pinking, detonation etc. and concentrated on the carbs.
They were stripped and blown out with compressed air and he reset the float valve heights. He then found some play in the CSP throttle linkage which was causing one side to open quicker than the other creating an imbalance. This was corrected as best as he could but will be replaced with a dual cable assembly as soon as I can find one. The pedal assembly upfront was worn and needs replacing too as this was preventing full throttle being achieved. We then did another run on the dyno and this simple carb work had given us another 16 bhp!
Alan said it was not worth spending and more time (and money) until the new parts were fitted and we finished for the day. He also recommended fitting the cold start mechanism so that's another few parts added to my list.
The van ran so much better on the way home and started first time on the key this morning despite some low temperatures overnight. I'll post another update after the parts are fitted and I've had another session on the rolling road.
The more stupid questions I ask, the smarter I get!