My fairly new build has got me stumped with a lean pop at partial throttle driving, or in neutral at low rpm. At WOT it runs like a raped ape. No detonation whatsoever, but the plugs are snow white every time I pull them. I've even cut the threads off to completely to expose the lower porcelain and it's all snow white (no particulate to indicate detonation either). I know this is a fairly common problem, but the usual suspects aren't the issue here. I've been up and down with this thing and I think I just need some fresh input.
It's basically a stock short block 302 in a 1989 Mustang GT. The relevant mods are GT40X heads (58cc with mild port blending), GT40 upper and lower intake, Compucam 2031, 1.72 Crane roller rockers, 65mm throttle body, Kirban afpr at 42 psi (without vauum), 24lb injectors, stock fuel rail, Walbro 255 lph in tank pump, C&L 75mm MAF with blue sample tube, C&L intake elbow, stock airbox, complete EGR system delete, MAC equal length headers into a 2.5" Prochamber and Pro dumps, SCT 4 bank Eliminator chip with a mail order tune for all of the aforementioned parts.
I've played with the fuel pressure a bit, and the less I give it the worse the problem gets. 42 psi is where the popping starts to go away, but adding more fuel pressure doesn't help it any. I've taken it up to 46 psi without vacuum.
I've pulled the codes, and none exist. Code 11 every time, in every tune position except the factory tune. This problem also existed before I installed the tunes, and whatever Bama did helped this problem and a few others, including low rpm bucking and not wanting to idle. I have done a cylinder balance test with all of the tunes, and I get Code 90 every time... I've even done it down to the third, most stringent parameter.
I reinstalled the factory airbox, in lieu of a Moroso CAI because this problem was MUCH worse with the CAI installed. As soon as I put the factory airbox back on the engine was just happier. I was leaning towards a MAF issue, but I've tried multiple known working sensors and none have shown any improvement. I have also tried clocking the C&L unit, and also tried shifting the factory airbox to try to get more consistent airflow over the sample tube.
o2 sensors are switching, and are grounded perfectly.
Distributor has been swapped with a known working unit, and so has the TFI module. Crane Cams Fireball ignition coil is working too.
I've been using AGSF-32c Motorcraft plugs, gapped at 0.044 since day one. I recently switched to Autolite AR103's gapped at 0.052 thinking that the step colder would help. I think it may be worse though.
Anyway I'm stumped. Any help is appreciated. The only thing I can think of at this point is that the C&L meter is total crap. I've alway used Pro-M meters, but this is all I had for this build. Should I try a black sample tube?
Thanks in advance!
edit: I forgot to mention the timing... Timing is at 12 degrees initial right now, but the weird thing is that no matter how much timing I give it, it won't ping or detonate. I had it cranked up to 20 degrees initial one day just to see if I could get it to detonate and it didn't at all. Maybe it's just too quiet to hear over the exhaust now, but I remember when this car was bone stock I couldn't get anymore than 12 degrees without hearing the marbles in a tin can sound. It's got a 50oz SFI approved damper from Ford Racing btw.
It's basically a stock short block 302 in a 1989 Mustang GT. The relevant mods are GT40X heads (58cc with mild port blending), GT40 upper and lower intake, Compucam 2031, 1.72 Crane roller rockers, 65mm throttle body, Kirban afpr at 42 psi (without vauum), 24lb injectors, stock fuel rail, Walbro 255 lph in tank pump, C&L 75mm MAF with blue sample tube, C&L intake elbow, stock airbox, complete EGR system delete, MAC equal length headers into a 2.5" Prochamber and Pro dumps, SCT 4 bank Eliminator chip with a mail order tune for all of the aforementioned parts.
I've played with the fuel pressure a bit, and the less I give it the worse the problem gets. 42 psi is where the popping starts to go away, but adding more fuel pressure doesn't help it any. I've taken it up to 46 psi without vacuum.
I've pulled the codes, and none exist. Code 11 every time, in every tune position except the factory tune. This problem also existed before I installed the tunes, and whatever Bama did helped this problem and a few others, including low rpm bucking and not wanting to idle. I have done a cylinder balance test with all of the tunes, and I get Code 90 every time... I've even done it down to the third, most stringent parameter.
I reinstalled the factory airbox, in lieu of a Moroso CAI because this problem was MUCH worse with the CAI installed. As soon as I put the factory airbox back on the engine was just happier. I was leaning towards a MAF issue, but I've tried multiple known working sensors and none have shown any improvement. I have also tried clocking the C&L unit, and also tried shifting the factory airbox to try to get more consistent airflow over the sample tube.
o2 sensors are switching, and are grounded perfectly.
Distributor has been swapped with a known working unit, and so has the TFI module. Crane Cams Fireball ignition coil is working too.
I've been using AGSF-32c Motorcraft plugs, gapped at 0.044 since day one. I recently switched to Autolite AR103's gapped at 0.052 thinking that the step colder would help. I think it may be worse though.
Anyway I'm stumped. Any help is appreciated. The only thing I can think of at this point is that the C&L meter is total crap. I've alway used Pro-M meters, but this is all I had for this build. Should I try a black sample tube?
Thanks in advance!
edit: I forgot to mention the timing... Timing is at 12 degrees initial right now, but the weird thing is that no matter how much timing I give it, it won't ping or detonate. I had it cranked up to 20 degrees initial one day just to see if I could get it to detonate and it didn't at all. Maybe it's just too quiet to hear over the exhaust now, but I remember when this car was bone stock I couldn't get anymore than 12 degrees without hearing the marbles in a tin can sound. It's got a 50oz SFI approved damper from Ford Racing btw.
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