I'm chasing an idle problem. The car idled fine before the last round of modifications. Then I added long tube headers, camshafts, and upgraded the fuel system to dual FPDMs and dual GT pumps. Since then the car has never idle quite right. (Driving is fine and it makes good power) The idle will drop below 500 and pop back up to the correct idle. Sometimes it will stall if I don't catch it with the throttle. I've band aided it by pulling timing and dialing in the dashpot trims, but it just isn't right. I'm thinking it has to do with one of the three changes above. I'm thinking that if anyone had the problems I'm having with headers or camshafts, they'd stop installing them, so I'm guessing fuel. I've modified the Fuel Pump Voltage table by data logging the corrected values from the ECU, but it didn't seem to help. What other tune related changes need to be made for the Dual FPDM/Dual pump setup? Does anyone have a Fuel Pump Voltage table they would like to share?
Idle Issue. Possible Fuel Pump tuning issue.
- Thread starter Bullitt5566
- Start date
the pump voltage table is only a feed forward as long as its not way out in left field its fine as the ecu saves a corrected kam table (as long as u dont disable it or reset the ecu kam) to maintain target deltaP
idle instability are going to be due to 1 of 4 possible causes
1) fuel variations, if in closed loop make sure its switching at stoich (some longtubes cant measure stoich at idle) and making small jumps (amplitude), since you have longtubes you need to make sure the correction delay isnt occuring before the o2 sees the adjustment made otherwise itll be trying to hit a moving target causing more idle oscillation
2) spark, the ecu throws around spark as a fine adjustment to correct for per cylinder and short term corrections, make sure the spark jumps arent too small that is cant correct and make sure its not too large making it oscillate, idle spark is determined by the feedback torque reserve function which is the target and based on the MBT spark table, the correction rate is the spk_fbs_gain scalar, the stock tq reserve function in the fbgi0 cals are absolute garbage and cause idle instability even on a bone stock cobra
3) the isc correction, make sure your not overtaxing the isc valve by making sure the iscdc is below 35% at idle, then check ipsibr and isckam and make sure they result in a sum of 0.0000 or near it, if you hadnt dialed in idle air then id recommend just adjusting the isc multiplier table to get it closer as its the least intrusive and wouldnt require any revamping
4) mechanically induced oscillations due to erraric combustion, this could be caused by a leaking fuel injector running one cylinder richer, a misfire causing the hego to report lean and as a result dumping fuel, a vac leak that affects cylinders unproportionately, or even a weak coil, fouled plug, etc.. anything mechanical could even be a wiped lobe on the cam or a leaky valve, exhaust leak, u name it
idle instability are going to be due to 1 of 4 possible causes
1) fuel variations, if in closed loop make sure its switching at stoich (some longtubes cant measure stoich at idle) and making small jumps (amplitude), since you have longtubes you need to make sure the correction delay isnt occuring before the o2 sees the adjustment made otherwise itll be trying to hit a moving target causing more idle oscillation
2) spark, the ecu throws around spark as a fine adjustment to correct for per cylinder and short term corrections, make sure the spark jumps arent too small that is cant correct and make sure its not too large making it oscillate, idle spark is determined by the feedback torque reserve function which is the target and based on the MBT spark table, the correction rate is the spk_fbs_gain scalar, the stock tq reserve function in the fbgi0 cals are absolute garbage and cause idle instability even on a bone stock cobra
3) the isc correction, make sure your not overtaxing the isc valve by making sure the iscdc is below 35% at idle, then check ipsibr and isckam and make sure they result in a sum of 0.0000 or near it, if you hadnt dialed in idle air then id recommend just adjusting the isc multiplier table to get it closer as its the least intrusive and wouldnt require any revamping
4) mechanically induced oscillations due to erraric combustion, this could be caused by a leaking fuel injector running one cylinder richer, a misfire causing the hego to report lean and as a result dumping fuel, a vac leak that affects cylinders unproportionately, or even a weak coil, fouled plug, etc.. anything mechanical could even be a wiped lobe on the cam or a leaky valve, exhaust leak, u name it
Thank you for the help. The fuel is spot on. I've also increased the O2 heater, time to go closed loop, and multiplied the O2 delay table by 1.5. The isc is right at 33% and the correction is around 0. I don't think it is a mechanical problem because it runs like a top, just doesn't idle. Pulling the spark back to 0 made the biggest difference, but I know that isn't the right answer because there's carbon spitting out of the tailpipes. The spark gain is .4 whereas 1.2 is default. (I'm using SCT PRP), the torque reserve is stock. How does the torque reserve function work? Thank you for your assistance.
the more tq reserve the less target timing at idle but the more spark can swing to compensate for variations
Good evening y'all,
Did you fix this problem?
Did you fix this problem?
Not yet. I disconnected one of the fuel pumps and FPDM, no change. I made the O2 timing changes decipha suggested. Didn't seem to help. I also changed out the injectors for known good ones. No change. This weekend I'm replacing the FRPS and O2 sensors with Motorcraft sensors. I'm also going to check the mechanical items, again, plugs & compression. After that I'll be moving the O2 sensor from the collector to one of the primary tubes on the long tube headers to eliminate delay and possible air leaks in the collector. Anyone have an idea which cylinders should be monitored with the bullitt intake? I know one is leaner than the others. If that doesn't work, the valve covers come off to check camshaft timing/balance. If that is fine, the stock cams go back in.
Your cams claim "big loping idle" Have you considered just increasing your base idle speed 50-100 rpm ?
I can't seem to find your exact cam specs, but I am sure they are similar to mine. Mine are 106 intake centerline, I had them installed straight up on the stock cam gears at 115 degrees for awhile until I bought adjustable gears, with them straight up the idle quality was poor and they ended up being slightly imbalanced bank to bank as well, I had to idle at 900 rpm to compensate for that. Once I degreed them in correctly and got them timed the same on both banks the idle quality was way better, but I still have to idle at around 750. Any lower and it's a little too rough and wants to stall at times.
So is your intake center line 110 degrees? If so did you degree them there? If not I would do that first, but most likely you will still end up needing a little more base idle speed.
I can't seem to find your exact cam specs, but I am sure they are similar to mine. Mine are 106 intake centerline, I had them installed straight up on the stock cam gears at 115 degrees for awhile until I bought adjustable gears, with them straight up the idle quality was poor and they ended up being slightly imbalanced bank to bank as well, I had to idle at 900 rpm to compensate for that. Once I degreed them in correctly and got them timed the same on both banks the idle quality was way better, but I still have to idle at around 750. Any lower and it's a little too rough and wants to stall at times.
So is your intake center line 110 degrees? If so did you degree them there? If not I would do that first, but most likely you will still end up needing a little more base idle speed.
I'm in the process of degreeing the cams. I assumed that since the pistons were fly cut and PTV clearance wasn't an issue I could get away with not degreeing, however I didn't consider left/right bank differences. Did you cams specify a 106 intake centerline? My comp cams specify 109, but if I'm degreeing I can set it to whatever. Is there a benefit to advancing them a few degrees?
Hey, yes you can get away with not degreeing as you found out, But the stock gears will put the cams at a 115 intake centerline, ( There can be slight variance, I actually found that my drivers side was at a 116.5 intake centerline) so you are losing out on a few degrees of advance. It's said that advancing will help the lower and mid rpm power while retard can benefit at higher rpm. I can tell you the most significant difference I really noticed after degreeing was the idle quality. I had planned to do a dyno pull after degreeing without any other changes just to see, but I could tell after driving it that it felt about the same and there wasn't a significant increase there, not enough to spend the money.
Mine did call for being set at 106, I would set your cams at where they are recommended at 109, that should help, but I bet that you will still need to up your idle speed 50 rpm or so to smooth things out, I have mine set for 755rpm and it ends up running between 760 -800 and it idles great, no complaints and no stalling or anything.
Mine did call for being set at 106, I would set your cams at where they are recommended at 109, that should help, but I bet that you will still need to up your idle speed 50 rpm or so to smooth things out, I have mine set for 755rpm and it ends up running between 760 -800 and it idles great, no complaints and no stalling or anything.
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I think I found the problem. Finally managed to get a solid, repeatable degree reading on the cams. (Degreeing the cams in the car is a story in itself) The driver side is at 110 ICL and the Pass side is at 102 ICL. Luckily the pistons are fly cut! I'm assuming the chain or something jumped during cam install.
Does it do it all of the time like 100% of the time or randomly?
Found the problem. The timing guide pivot bolt broke on the pass side. Luckily it just caused erratic idling and not much more. Sounds like a common problem with TEKSID blocks running the stock 6mm guide bolts with higher rate springs and after market cams. Time to upgrade.
OH wow, good to know and I'm glad you found that and no further damage done !
yea you should always upgrade them even on a stock rebuild, interesting the passenger side failed, i find the driver side of the engine is always tighter going together I figured that would be more likely to snap first
Finally fixed. Replaced both pivot bolts with 8mm ones. I modified the tensioners too. The broken pin fell into the pan so I had to drop the K member to retrieve it. I set the ICL timing at 108.5 for both sides. I interestingly the my cam ICL was 102 for the pass side and 110 for the driver side. I thought the broken pin caused the timing to be off but actually it was a set of aftermarket cam sprockets that caused it. After all of that the idle is only slightly better.
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