87 951 VEMS Install
09-27-2019, 01:34 AM
#526
Three Wheelin'
If you have a chance, could you measure voltage drop on DME pins 18 and 35. DME 18 goes to Vems ECU 25. I measured voltage drop to 10.8V during cranking with hi torque starter and quest alternator combo. This is with a new battery fully charged at 12.8V. Beginning to suspect, vems ecu is very sensitive with voltage drop which is causing trigger syncing issues with timing, causing startup problems. I'm starting to get it every now and then again. Investigating if it's starter and / or alternator related. I've noticed on good starts, tachometer will Rev to 1200rpm or more. Where as a bad start will be below 1k rpm. It's either the starter is faulty causing a big voltage drop causing vems to be confused. Or voltage drop related to starter/alternator combo. So far I've tried to put an amplifier battery capacitor with ecu but it did not correct issue. Will try a seperate battery ( is this even ok to do?) and report back. Also suspect that my starter/alternator could be faulty as I bought them used with an Ice Shark battery cable here on the list many years ago. So if you have this starter/alternator combo without issues, I would like to know. Much Appreciated. - Wayne
At my shop, we often replace 996/997 and early Cayenne starters for excessive current draw (and hence voltage drop), but this generally results in noticeably slow cranking while starting, even with a fresh and fully charged battery. If you can find a shop with a Snap-On VAT40 or equivalent battery/starter system tester with high-voltage amp clamp, this can be easily tested by clamping around one of the battery cables and observing current draw while cranking. To be honest, I have not done this test on a 944 engine, but the engines/starters mentioned above draw about 250 amps while cranking with a good starter, and 400+ with a worn starter. Note that if a voltage drop due to a bad connection/high resistance is the problem, the starter will actually draw LESS current (Ohm's law).
09-27-2019, 03:56 PM
#527
Rennlist Member
I rarely advocate parts-swapping, but because the starter is one of the few easy components to swap out in the 951, why not find a good used stock 944 starter and swap it in to see if things change?
At my shop, we often replace 996/997 and early Cayenne starters for excessive current draw (and hence voltage drop), but this generally results in noticeably slow cranking while starting, even with a fresh and fully charged battery. If you can find a shop with a Snap-On VAT40 or equivalent battery/starter system tester with high-voltage amp clamp, this can be easily tested by clamping around one of the battery cables and observing current draw while cranking. To be honest, I have not done this test on a 944 engine, but the engines/starters mentioned above draw about 250 amps while cranking with a good starter, and 400+ with a worn starter. Note that if a voltage drop due to a bad connection/high resistance is the problem, the starter will actually draw LESS current (Ohm's law).
At my shop, we often replace 996/997 and early Cayenne starters for excessive current draw (and hence voltage drop), but this generally results in noticeably slow cranking while starting, even with a fresh and fully charged battery. If you can find a shop with a Snap-On VAT40 or equivalent battery/starter system tester with high-voltage amp clamp, this can be easily tested by clamping around one of the battery cables and observing current draw while cranking. To be honest, I have not done this test on a 944 engine, but the engines/starters mentioned above draw about 250 amps while cranking with a good starter, and 400+ with a worn starter. Note that if a voltage drop due to a bad connection/high resistance is the problem, the starter will actually draw LESS current (Ohm's law).
09-27-2019, 04:00 PM
#528
Rennlist Member
Check post #229 onward. Someone similar had the same issue. Maybe your config is corrupt. I would contact peep to get a good known config and upload.
09-27-2019, 08:58 PM
#529
Three Wheelin'
I would like to find a good used unit to swap in but used 944 parts in Hawaii is very scarce. I would like to buy a used one off of ebay, but a used one costs as much as a rebuilt, add shipping itll cost as much as the IMI hi torque start, since they offer free shipping, lol go figure. Ill remove the starter and go have it tested at a shop, maybe Oreilys or Autozone might have a tester. Ill test the battery and starter cables again, they look new when I installed them, but I can test resistance and voltage drops. BTW, according to the IMI, their hi torque starter supposed to draw less amperage than a factory starter would, which is why I suspect it being faulty.
10-23-2019, 09:36 PM
#531
Advanced
Yes - DME does not control A/C, so it will turn on with VEMS. However you should run the compressor spower wire through a relay to send a ground to VEMS to up the RPM when A/C is on.
Like this image - I have run this by Peep and he says it is correct
10-24-2019, 07:37 AM
#532
Three Wheelin'
Once relay is wired up, what needs to be done in VEMS to up idle on signal ?
10-24-2019, 08:37 AM
#533
Advanced
11-13-2019, 08:52 AM
#534
5th Gear
Join Date: Apr 2004
Location: MA
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Questions for those who have replaced the Bosch Motronic with the VEMS ECU.
1. Did you buy a generic VEMS unit from an authorized reseller and roll your own wire harness?
Or
2. Did you buy a vehicle specific “PnP” unit from Peep Päädam at Stuttcars.com?
a. If yes, what were the payment terms and lead-time to receive the equipment?
3. The VEMS supports three types of ignition
a. Traditional coil, cap and rotor
b. Wasted spark system
c. Coil over plug
My question is what are the pros and cons of option b and c?
1. Did you buy a generic VEMS unit from an authorized reseller and roll your own wire harness?
Or
2. Did you buy a vehicle specific “PnP” unit from Peep Päädam at Stuttcars.com?
a. If yes, what were the payment terms and lead-time to receive the equipment?
3. The VEMS supports three types of ignition
a. Traditional coil, cap and rotor
b. Wasted spark system
c. Coil over plug
My question is what are the pros and cons of option b and c?
11-13-2019, 11:45 AM
#535
Pro
Bought from Peep - I needed something that would work out of the box, and it did!
Payment terms were `wire transfer to bank in Estonia' - Generally I would NEVER do this, but Peep has a solid reputation.
Delivery took a bit longer than I hoped, but Peep was traveling at the time of my order.
I've previously read that wasted spark is mostly beneficial for engines with more than 4 cylinders, so I'm curious what others here think. I would l like to upgrade from the stock 944 ignition system...
Payment terms were `wire transfer to bank in Estonia' - Generally I would NEVER do this, but Peep has a solid reputation.
Delivery took a bit longer than I hoped, but Peep was traveling at the time of my order.
I've previously read that wasted spark is mostly beneficial for engines with more than 4 cylinders, so I'm curious what others here think. I would l like to upgrade from the stock 944 ignition system...
Questions for those who have replaced the Bosch Motronic with the VEMS ECU.
1. Did you buy a generic VEMS unit from an authorized reseller and roll your own wire harness?
Or
2. Did you buy a vehicle specific “PnP” unit from Peep Päädam at Stuttcars.com?
a. If yes, what were the payment terms and lead-time to receive the equipment?
3. The VEMS supports three types of ignition
a. Traditional coil, cap and rotor
b. Wasted spark system
c. Coil over plug
My question is what are the pros and cons of option b and c?
1. Did you buy a generic VEMS unit from an authorized reseller and roll your own wire harness?
Or
2. Did you buy a vehicle specific “PnP” unit from Peep Päädam at Stuttcars.com?
a. If yes, what were the payment terms and lead-time to receive the equipment?
3. The VEMS supports three types of ignition
a. Traditional coil, cap and rotor
b. Wasted spark system
c. Coil over plug
My question is what are the pros and cons of option b and c?
11-13-2019, 12:35 PM
#536
Rennlist Member
Questions for those who have replaced the Bosch Motronic with the VEMS ECU.
1. Did you buy a generic VEMS unit from an authorized reseller and roll your own wire harness?
Or
2. Did you buy a vehicle specific “PnP” unit from Peep Päädam at Stuttcars.com?
a. If yes, what were the payment terms and lead-time to receive the equipment?
3. The VEMS supports three types of ignition
a. Traditional coil, cap and rotor
b. Wasted spark system
c. Coil over plug
My question is what are the pros and cons of option b and c?
1. Did you buy a generic VEMS unit from an authorized reseller and roll your own wire harness?
Or
2. Did you buy a vehicle specific “PnP” unit from Peep Päädam at Stuttcars.com?
a. If yes, what were the payment terms and lead-time to receive the equipment?
3. The VEMS supports three types of ignition
a. Traditional coil, cap and rotor
b. Wasted spark system
c. Coil over plug
My question is what are the pros and cons of option b and c?
I believe all of us here bought it PnP from Peep. Money was transferred via TransferWise website ( similar to PayPal ). Time to order, assemble and ship to Hawaii took 1 month. My repair took 2 months. If you go traditional cap and rotor, you are able to use stock ignition if you already have a good system. Wasted spark, there is some wiring to do and mounting of wasted spark coil but in return you get the most reliable spark ( best for high boost/rpm conditions ). Coil on Plug, from what I know is not compatible with 8V heads as there is no good way to secure COP coils. Though Im exploring options at the moment as I am trying to keep engine bay clean and will attempt to perform a wire tuck.
11-13-2019, 01:48 PM
#537
I'm also in Hawaii and contacted Peep through FB. His reputation is solid and I did the TransferWise too. I have wasted spark too (Peeps add-on option). No cap, no rotor....more dependable and modern tech and parts replace mechanical. All good.
12-17-2019, 08:07 AM
#538
I'm looking for help to get my car running at low temperatures -
It's running fine when warm, idle is stable.
It was always starting with the old DME, regardless of weather.
However right now, it dies right after cranking.
Logical thing to do is to raise enrichment, right? I did that, cranking, afterstart, warmup - all raised in various combinations, no difference.
I suspect the IAC is the culprit, since the car is running rich enough (lambda goes down to 0.65 before dying) but makes no effort to raise RPM and will stay running if I touch the throttle lightly, raising RPM to ~1100-1200.
Can you share screenshots of your idle / IAC settings? I've got the 3-wire IAC and I'm not sure how to configure channels, the ref curve etc.
It's running fine when warm, idle is stable.
It was always starting with the old DME, regardless of weather.
However right now, it dies right after cranking.
Logical thing to do is to raise enrichment, right? I did that, cranking, afterstart, warmup - all raised in various combinations, no difference.
I suspect the IAC is the culprit, since the car is running rich enough (lambda goes down to 0.65 before dying) but makes no effort to raise RPM and will stay running if I touch the throttle lightly, raising RPM to ~1100-1200.
Can you share screenshots of your idle / IAC settings? I've got the 3-wire IAC and I'm not sure how to configure channels, the ref curve etc.
12-17-2019, 11:24 AM
#540
I'm looking for help to get my car running at low temperatures -
It's running fine when warm, idle is stable.
It was always starting with the old DME, regardless of weather.
However right now, it dies right after cranking.
Logical thing to do is to raise enrichment, right? I did that, cranking, afterstart, warmup - all raised in various combinations, no difference.
I suspect the IAC is the culprit, since the car is running rich enough (lambda goes down to 0.65 before dying) but makes no effort to raise RPM and will stay running if I touch the throttle lightly, raising RPM to ~1100-1200.
Can you share screenshots of your idle / IAC settings? I've got the 3-wire IAC and I'm not sure how to configure channels, the ref curve etc.
It's running fine when warm, idle is stable.
It was always starting with the old DME, regardless of weather.
However right now, it dies right after cranking.
Logical thing to do is to raise enrichment, right? I did that, cranking, afterstart, warmup - all raised in various combinations, no difference.
I suspect the IAC is the culprit, since the car is running rich enough (lambda goes down to 0.65 before dying) but makes no effort to raise RPM and will stay running if I touch the throttle lightly, raising RPM to ~1100-1200.
Can you share screenshots of your idle / IAC settings? I've got the 3-wire IAC and I'm not sure how to configure channels, the ref curve etc.