Turbo'd 8 keeps dying and/or misfiring
08-11-2013, 07:09 PM
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Turbo'd 8 keeps dying and/or misfiring
So I bought a turbo'd 8 and immediately flooded the thing. Long story short, I replaced plugs, coils, wires, starter, and the battery.
Now she cranks fine and warmup idle is pretty solid (it gets a little low sporadically, but not enough that it will die). I took the car for a test drive just now and it's smooth under 35mph. When I let her rip, I got misfires, the flashing CEL, and the engine would usually die shortly thereafter.
When I'm driving normally and press the clutch above 3500rpm, the car should find idle but doesn't... it just dies.
One other thing to note is that it backfires almost every time I left off the throttle.
Car has a greddy turbo and the previous owner tuned it with a Cobb.
What could be going on here? Being an something of a n00b when it comes to FI and the 8, I'm looking for some feedback and recommended troubleshooting steps.
Any help is greatly appreciated.
Now she cranks fine and warmup idle is pretty solid (it gets a little low sporadically, but not enough that it will die). I took the car for a test drive just now and it's smooth under 35mph. When I let her rip, I got misfires, the flashing CEL, and the engine would usually die shortly thereafter.
When I'm driving normally and press the clutch above 3500rpm, the car should find idle but doesn't... it just dies.
One other thing to note is that it backfires almost every time I left off the throttle.
Car has a greddy turbo and the previous owner tuned it with a Cobb.
What could be going on here? Being an something of a n00b when it comes to FI and the 8, I'm looking for some feedback and recommended troubleshooting steps.
Any help is greatly appreciated.
08-11-2013, 08:06 PM
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RIWWP just posted a how to find a vacuum leak thread.
It's not exactly a DIY but it's good.
And maybe some data logs might help.
Can you post any of those?
It's not exactly a DIY but it's good.
And maybe some data logs might help.
Can you post any of those?
Last edited by EviLStewie; 08-11-2013 at 08:26 PM.
08-11-2013, 08:06 PM
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At idle, positive short term fuel trim and MAF g/s less than 5.0.
5.5g/s should be normal idle for most Renesis engines, plus or minus a few tenths. Once you get under 5.0, air is getting to the engine that isn't passing the MAF. The ECU is under fueling then, and the STFT goes positive as the ECU tries to correct.
5.5g/s should be normal idle for most Renesis engines, plus or minus a few tenths. Once you get under 5.0, air is getting to the engine that isn't passing the MAF. The ECU is under fueling then, and the STFT goes positive as the ECU tries to correct.
Last edited by RIWWP; 08-11-2013 at 08:09 PM.
08-11-2013, 08:29 PM
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Mmmm maybe a boosted 8 might have been a bite more than you can chew.
Acquiring a data log using the Cobb AP is not hard, the option is right there in the list.
After gathering the log files use the AP Manager to transfer them to your computer.
(basically plug your AP in to your computer)
08-11-2013, 08:30 PM
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At idle, positive short term fuel trim and MAF g/s less than 5.0.
5.5g/s should be normal idle for most Renesis engines, plus or minus a few tenths. Once you get under 5.0, air is getting to the engine that isn't passing the MAF. The ECU is under fueling then, and the STFT goes positive as the ECU tries to correct.
5.5g/s should be normal idle for most Renesis engines, plus or minus a few tenths. Once you get under 5.0, air is getting to the engine that isn't passing the MAF. The ECU is under fueling then, and the STFT goes positive as the ECU tries to correct.
I have a Cobb but haven't yet to turn it on. Guess I'll have to get on it!
Thanks,
Mike
08-12-2013, 07:16 AM
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You can get that info without having to data log, just pull up the appropriate metric on the screen with the COBB plugged in. Data logging the main parameters during the problem points and posting it here would help people figure your issue out, so learn how to do that too.
08-15-2013, 09:05 PM
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At idle, positive short term fuel trim and MAF g/s less than 5.0.
5.5g/s should be normal idle for most Renesis engines, plus or minus a few tenths. Once you get under 5.0, air is getting to the engine that isn't passing the MAF. The ECU is under fueling then, and the STFT goes positive as the ECU tries to correct.
5.5g/s should be normal idle for most Renesis engines, plus or minus a few tenths. Once you get under 5.0, air is getting to the engine that isn't passing the MAF. The ECU is under fueling then, and the STFT goes positive as the ECU tries to correct.
At idle, MAF g/s hovers around 6.6 and short term FT bounces between positive and negative quite a bit. I attached the log if anyone wants to take a look.
Thoughts?
Last edited by BigMikeATL; 08-15-2013 at 09:09 PM.
08-15-2013, 09:09 PM
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As a side note, i swapped out the coils, cleaned the MAF, and tightened some of the couplers on the intake. The datalog was taken tonight after all of that was done. The car doesn't seem to misfire anymore and doesn't stall as easily, though it did stall a couple times if I pressed the clutch in after coming down from 3-4k revs.
It also seems to studder or gurgle (for lack of a better term) when I'm feathering the throttle and it still backfires like crazy.
It also seems to studder or gurgle (for lack of a better term) when I'm feathering the throttle and it still backfires like crazy.
08-15-2013, 09:23 PM
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08-16-2013, 08:10 AM
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it must be vta from all the backfiring reports.
08-16-2013, 08:52 AM
#17
OP I would beat on a vacuum leak, Stalling at idle after a cruise is almost always a vacuum leak as the car does not correct the fuel trims and will stall out.
So a positive STFT is always a vacuum leak? even if its only 1 or 2?
At idle, positive short term fuel trim and MAF g/s less than 5.0.
5.5g/s should be normal idle for most Renesis engines, plus or minus a few tenths. Once you get under 5.0, air is getting to the engine that isn't passing the MAF. The ECU is under fueling then, and the STFT goes positive as the ECU tries to correct.
5.5g/s should be normal idle for most Renesis engines, plus or minus a few tenths. Once you get under 5.0, air is getting to the engine that isn't passing the MAF. The ECU is under fueling then, and the STFT goes positive as the ECU tries to correct.
08-16-2013, 08:54 AM
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Your AFRs aren't steady, which is why your STFT flutters around. I'd expect it to be steadier than you have it. This could be a side effect of showing a higher g/s air flow than normal? The smarter tuners may have a better insight, but that doesn't look like a normal idle log to me.
08-16-2013, 09:03 AM
#19
Your AFRs aren't steady, which is why your STFT flutters around. I'd expect it to be steadier than you have it. This could be a side effect of showing a higher g/s air flow than normal? The smarter tuners may have a better insight, but that doesn't look like a normal idle log to me.
Is your MAF the stock scaling? if not what is it adjusted by?
You really should log more to, it would be nice to see ign seperation and MAF voltage.
Intake temp seems high, but I am used to NA and buffalo weather mine rarely gets more than 2 degrees above ambient, hopefully one of the FI guys can lend a hand there.
BOV; Recirc of VTA?
08-16-2013, 09:11 AM
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It's the HKS Super SQV. I believe it's VTA.
I'm hoping the engine can be tuned to reduce backfiring.
I'm trying to track down a pro in metro-Atlanta to tune it, else I'll reach out to MazdaManiac.
I'm hoping the engine can be tuned to reduce backfiring.
I'm trying to track down a pro in metro-Atlanta to tune it, else I'll reach out to MazdaManiac.
Last edited by BigMikeATL; 08-16-2013 at 09:14 AM.
08-16-2013, 09:18 AM
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No, since it can actually be trimmed there due to other factors. I would look for a positive STFT of at least +4% along with MAF below 5.0g/s.
It's been pretty consistent over the years that our engines take about 5.5g/s of air flow at idle, plus or minus a bit based on sensor variances, probably compression health, etc... If the MAF is recording under this, then it's not the engine miraculously running on far less of an air/fuel charge, it means that air is getting into the engine that isn't passing the MAF, i.e, a vacuum leak. A positive STFT would confirm it, as the O2 sensor would be seeing leaner AFRs than it would expect for ~4.5g/s or whatever, and has to add fuel.
I had a pinprick vacuum leak in a gasket between the UIM and LIM on the runner that sits against the firewall, and it generated a ~4.5-4.6g/s MAF and +5% STFT. I doubt a vacuum leak that produces a smaller gap is possible, but I wouldn't rule it out.
This doesn't really exist within his log.
I have only guesses as to what would generate a higher g/s than normal. Among them are: faulty MAF, MAF scaling messed up some weird way, different intake tube diameter at the MAF (and within several inches before and after it), or something getting onto the MAF to over-cool it consistently.
The presence of a turbocharger system adds complexity and fault points, but shouldn't have any impact on these points at idle.
It's been pretty consistent over the years that our engines take about 5.5g/s of air flow at idle, plus or minus a bit based on sensor variances, probably compression health, etc... If the MAF is recording under this, then it's not the engine miraculously running on far less of an air/fuel charge, it means that air is getting into the engine that isn't passing the MAF, i.e, a vacuum leak. A positive STFT would confirm it, as the O2 sensor would be seeing leaner AFRs than it would expect for ~4.5g/s or whatever, and has to add fuel.
I had a pinprick vacuum leak in a gasket between the UIM and LIM on the runner that sits against the firewall, and it generated a ~4.5-4.6g/s MAF and +5% STFT. I doubt a vacuum leak that produces a smaller gap is possible, but I wouldn't rule it out.
This doesn't really exist within his log.
I have only guesses as to what would generate a higher g/s than normal. Among them are: faulty MAF, MAF scaling messed up some weird way, different intake tube diameter at the MAF (and within several inches before and after it), or something getting onto the MAF to over-cool it consistently.
The presence of a turbocharger system adds complexity and fault points, but shouldn't have any impact on these points at idle.
08-16-2013, 09:21 AM
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08-16-2013, 09:23 AM
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No, since it can actually be trimmed there due to other factors. I would look for a positive STFT of at least +4% along with MAF below 5.0g/s.
It's been pretty consistent over the years that our engines take about 5.5g/s of air flow at idle, plus or minus a bit based on sensor variances, probably compression health, etc... If the MAF is recording under this, then it's not the engine miraculously running on far less of an air/fuel charge, it means that air is getting into the engine that isn't passing the MAF, i.e, a vacuum leak. A positive STFT would confirm it, as the O2 sensor would be seeing leaner AFRs than it would expect for ~4.5g/s or whatever, and has to add fuel.
I had a pinprick vacuum leak in a gasket between the UIM and LIM on the runner that sits against the firewall, and it generated a ~4.5-4.6g/s MAF and +5% STFT. I doubt a vacuum leak that produces a smaller gap is possible, but I wouldn't rule it out.
This doesn't really exist within his log.
I have only guesses as to what would generate a higher g/s than normal. Among them are: faulty MAF, MAF scaling messed up some weird way, different intake tube diameter at the MAF (and within several inches before and after it), or something getting onto the MAF to over-cool it consistently.
The presence of a turbocharger system adds complexity and fault points, but shouldn't have any impact on these points at idle.
It's been pretty consistent over the years that our engines take about 5.5g/s of air flow at idle, plus or minus a bit based on sensor variances, probably compression health, etc... If the MAF is recording under this, then it's not the engine miraculously running on far less of an air/fuel charge, it means that air is getting into the engine that isn't passing the MAF, i.e, a vacuum leak. A positive STFT would confirm it, as the O2 sensor would be seeing leaner AFRs than it would expect for ~4.5g/s or whatever, and has to add fuel.
I had a pinprick vacuum leak in a gasket between the UIM and LIM on the runner that sits against the firewall, and it generated a ~4.5-4.6g/s MAF and +5% STFT. I doubt a vacuum leak that produces a smaller gap is possible, but I wouldn't rule it out.
This doesn't really exist within his log.
I have only guesses as to what would generate a higher g/s than normal. Among them are: faulty MAF, MAF scaling messed up some weird way, different intake tube diameter at the MAF (and within several inches before and after it), or something getting onto the MAF to over-cool it consistently.
The presence of a turbocharger system adds complexity and fault points, but shouldn't have any impact on these points at idle.