Blown353
08-11-2006, 07:40 AM
OK, have a idle quality & tuning question.
I just did a FI changeover on a friend's road race Mustang. A little background:
The engine is a 402. I don't know the exact cam specs but it's a solid roller running about .740/.730 lift, high 260-something duration @ .050, 106 LSA. 13.7:1 SCR, aluminum block, heavily massaged Brodix aluminum heads. In a word: freakin' cool in a car that weighs about 2500#, dry sump, jerico 4-speed crashbox, flared fenders and 275/315 Hoosiers on the corners, TCP suspension.
When I was called in to assist the car had a Weber-based IR setup converted to EFI with 36# injectors. The stacks & blades were way too small and the engine was out of air at about 5000 rpm (which was good because it also ran out of injector at the same time so the "restrictor plate" IR setup saved the engine.)
Because of the prohibitive cost of reworking the Weber-based IR setup to be able to feed the engine enough air we converted it using a Victor EFI manifold, Accel 1500 cfm throttle body (a problem piece I will never use again, but I went with it at the request of the owner), 55# injectors, FAST ECU in B2B mode. No IAC currently. Fuel system consists of a Fuel-Safe cell, Aeromotive A1000 pump, 10 micron filter, Aeromotive regulator non-referenced and set at 45 PSI.
I tuned the driving and WOT areas of the map in short order and it runs great but I cannot get this thing to idle worth a damn, it surges badly from 1300 down to 400rpm where it nearly dies then "catches" itself and flares back up. It does this on a period of about 10 seconds. Given the cam specs I don't expect a perfect idle but I was expecting it to hold a fairly steady idle in the 1300rpm range.
With the IR setup it idled steady at about 1200-1300 rpm. I know an IR setup can really tame a cam with a lot of duration and overlap but the idle quality of the new single plane is nothing short of terrible and if I want to get rid of the surges I have to bump it up to the 2000-2200rpm range.
Here's the behavior: the engine will idle at 1300 for about 8-10 seconds, then it seems to load up and the RPM's dip way down to 400 or so, then it catches and revs back up with a little puff of black smoke. My first thought was fluctuating WB02 corrections causing the idle speed surge but it will still surge just as badly running open loop. In the 1300rpm range I've tried making it very lean and very rich and all A/F in between; no matter how much fuel I give it, it still does the surge to 400 rpm every 10 seconds or so. It is not MAP AE or anything like that dumping extra fuel from manifold vacuum fluctuations (checked that) and the throttle plates aren't fluttering. I've tried enabling timing trim @ idle and it doesn't help things at all. I've also tried more and less timing at idle to no avail, still surges like crazy and in the same way.
When the car is idling @ 1300rpm between surges it's pulling about 10" of vacuum which should be plenty of signal for the ECU to maintain idle quality.
Any other thoughts? I was going to try setting it up Alpha-N tonight and just letting it idle to see what happens but my hunch is it will still surge. I will also check everything again for vacuum leaks that could be causing the problem.
Trying to get this sucker ready to go playing up at Thunderhill this weekend.
Thanks in advance...
I just did a FI changeover on a friend's road race Mustang. A little background:
The engine is a 402. I don't know the exact cam specs but it's a solid roller running about .740/.730 lift, high 260-something duration @ .050, 106 LSA. 13.7:1 SCR, aluminum block, heavily massaged Brodix aluminum heads. In a word: freakin' cool in a car that weighs about 2500#, dry sump, jerico 4-speed crashbox, flared fenders and 275/315 Hoosiers on the corners, TCP suspension.
When I was called in to assist the car had a Weber-based IR setup converted to EFI with 36# injectors. The stacks & blades were way too small and the engine was out of air at about 5000 rpm (which was good because it also ran out of injector at the same time so the "restrictor plate" IR setup saved the engine.)
Because of the prohibitive cost of reworking the Weber-based IR setup to be able to feed the engine enough air we converted it using a Victor EFI manifold, Accel 1500 cfm throttle body (a problem piece I will never use again, but I went with it at the request of the owner), 55# injectors, FAST ECU in B2B mode. No IAC currently. Fuel system consists of a Fuel-Safe cell, Aeromotive A1000 pump, 10 micron filter, Aeromotive regulator non-referenced and set at 45 PSI.
I tuned the driving and WOT areas of the map in short order and it runs great but I cannot get this thing to idle worth a damn, it surges badly from 1300 down to 400rpm where it nearly dies then "catches" itself and flares back up. It does this on a period of about 10 seconds. Given the cam specs I don't expect a perfect idle but I was expecting it to hold a fairly steady idle in the 1300rpm range.
With the IR setup it idled steady at about 1200-1300 rpm. I know an IR setup can really tame a cam with a lot of duration and overlap but the idle quality of the new single plane is nothing short of terrible and if I want to get rid of the surges I have to bump it up to the 2000-2200rpm range.
Here's the behavior: the engine will idle at 1300 for about 8-10 seconds, then it seems to load up and the RPM's dip way down to 400 or so, then it catches and revs back up with a little puff of black smoke. My first thought was fluctuating WB02 corrections causing the idle speed surge but it will still surge just as badly running open loop. In the 1300rpm range I've tried making it very lean and very rich and all A/F in between; no matter how much fuel I give it, it still does the surge to 400 rpm every 10 seconds or so. It is not MAP AE or anything like that dumping extra fuel from manifold vacuum fluctuations (checked that) and the throttle plates aren't fluttering. I've tried enabling timing trim @ idle and it doesn't help things at all. I've also tried more and less timing at idle to no avail, still surges like crazy and in the same way.
When the car is idling @ 1300rpm between surges it's pulling about 10" of vacuum which should be plenty of signal for the ECU to maintain idle quality.
Any other thoughts? I was going to try setting it up Alpha-N tonight and just letting it idle to see what happens but my hunch is it will still surge. I will also check everything again for vacuum leaks that could be causing the problem.
Trying to get this sucker ready to go playing up at Thunderhill this weekend.
Thanks in advance...