DFI and ECMDiscuss all aspects of DFI (Digital Fuel Injection), ECMs (Electronic Control Module), scanners, and diagnostic equipment. Fine tune your Third Gen computer system for top performance.
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Hi guys.
After spending hours trying to tune my new engine I turn to you for help and advice.
My combo: -385cid (4.040”*3.75”), AFR 180cc w/66cc, -CR 10.47:1, -DCR 8.33:1, -quench distance 0.039”, -CompCam hyd. roller -Holley Stealth Ram induction, -Holley commander 950MPFI, electronically controlled ignition, -MSD distributor 8366, -MSD 6AL, -MSD Blaster2 coil, new MSD spark plug wires 8.5mm, -new spark plugs.
The problem I have is to tune the idle. It will not idle “decent”. The camshaft supposes to have a mild rough idle, but the engine shakes the car when it idle. The camshaft was degreed on installation. I have tried to adjust the air/fuel mix(12.5:1 – 17:1) and the timing(2 – 30 BTDC), and yes, I have also checked the timing with a timing light. Nothing helps. Reg. the timing, it doesn’t seem like changing it have much effect at all.
Do you have any similarly experience?
Appreciate any reply
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there is a idle fix for the command 950, i dont remember wat it was. I have the c950 i had the same issue. do you have a wideband? check out chevytalk, they can help you with c950.
Hi jayk2k3, sorry for late replay, just came home from a 3day road tripp to Denmark.
I do have WB sensor.
If you are thinking about the "Idle Spark Control", it doesn't do anything to help a better idle. That in it self worry's me, can my engine be self igniting? Even though the CR is high, I don't think it's to high. Here in Norway we have 98 gas. Also I have the knock sensor.
When it's idling, does the red cell in the fuel map stay in one cell or is it jumping all over the place? Does your knock sensor indicate detonation at idle? Is your timing syncronized? How are your motor mounts? If you want, you can email me your .950 file so I can check it out.
The red cell doesn't move around, maybee up/down/sidevise 1 cell when it's idling. In prosess of calming down the idle I have flatened the timing/fuel map. The timing is syncronized.
The motor mounts seems to be in god condition.
I would very much like help from you to go through the 950file. Unfortunatly my internet laptop have Vista, and Vista don't work with my 950. I use my old laptop with windows98 to work with the car. I have tryed memorystick, floppydisk and CD, but it seems like it is impossible for me to get the file's over to the internet laptop and send them to you. I'm going to instal XP on my new laptop and hope that will work with the commander950.
Let me get back to you reg. when I have the files ready.
Hi guys. I’m sent off to work, on a ship for 4 weeks. I have limited excess to internet. When it comes to the knock sensor, the wiring kit said to connect the wire to the ECM at terminal B7. But when I open the Input/Output window in the 950 it seems like the “Timing Retard” should be connected to B8! Woody at Holley tech support told me the sensor would work if I just connected it to B7, without any further settings.
In process of tuning the idle I have used the log data function, but I have never seen any sign of knock registration. And that makes me wonder if I have the knock module connected to the correct terminal. Which terminal have you connected the knock module to?
As long as you followed the instructions here it should work correctly. Testing the knock retard is easy to do. Make sure you have values other than zero in the knock control settings. At idle, start a datalog and tap on the engine block with a hammer. Then view the datalog to see if it retarded the timing when you were tapping.
Thanks, I’ll try the tap test when I get back home. I used that same instruction sheet you referred to. How much initial timing do you think my combo should have at idle?
I'm no expert, but I would try 30° and 13.5:1 afr at idle. Then, if you are able to stabilize the idle, I would lean it out to 14:1, and then 14.5:1 if the engine stays smooth.
I’m no expert either. And I have never understood why the HSR require/like more initial timing than any other induction system I have read articles about. Considering combustion engines like SBC are most efficient when the cylinder pressure peaks at 14 degree ATDC, it seems to me that the early timing must have something to do with the way the air and fuel mixes before it enters the combustion chamber. This actual air/fuel mixture must influence the speed of the flame front. The shape of combustion chamber and the top of the piston, in addition to the position of the spark plug would definitive have something to do with how fast the flame front moves across the combustion chamber. Slow flame front require earlyer initial timing, and fast flame front allows later initial timing.
The less initial timing you engine needs to crank out most ponies, the more efficient it is. A slow buildup of cylinder pressure (slow flame front) means that the piston must travel upward a longer distance after the burn of gas has started.
When I load the supplied Holley spark map which fits best with my combo the initial timing are 22 degree at idle and 38 degree at WOT. Articles I have read in magazines shows that most SBC are most efficient at 36 degree WOT, and often idle at around 16 degree.
For street engines, have any of you experiences where you have to have initial timing set to more than 16 degree at idle and more than 38 degree at WOT? If you do, what do you think is the reason for that?
The 16° of initial timing is not factoring in the vacuum advance for those engines in the magazines. When they plug in the vacuum advance after setting the initial, that will add another ~16-18°. Since you have complete timing control with the 950, you need higher initial values to compensate for the lack of vacuum advance. That means values in the lower-mid 30's.
Hi, yust got back home from 4 weeks at sea. My car is still in the garage, haven't had time to take it out and/or work on it. However, I did messure the cranking pressure to 195psi on cold engine. From what I have read 195psi is in the upper range for a street engine (remember that we in Norway have 98 on the gaspump).
When I picked out parts for my engine project, I planed to end up more on the uper side compressionvise. I hope I was not to agressive picking out parts????
A litle update. Got some time to worke on the car today. It ran terrible. Anyway, there was a bad connection in the coil tower. After fixing the coil the engine idle ok to tune it.
After talking to Holley support I tryed to tune the engine in open mode.
I have two wide band A/F sensors, one supplyed from holley, and an other one from Zeitronix.
Even though the target A/F is set to as low as 13, the messured A/F is 16+ on the right bank and aprox. 15 on the left bank. Which one is most correct?. The spark plug are all new. The sensors are placed in collectors in thehooker 2055's.
After working on the tuning I cleaned the spark plugs. In the same prosess I messured the cranking compression pressure, this time with the engine warm. 205psi was messured, is this to hight?
BTW, did the tap test to. My Knock sensor is working
