New car has a problem
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Teching In
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That's to be expected. You can't just slap the new MAF on. You have to run the car through the PCM relearn procedure. It would currently trimmed for the foul MAF. You should drive the car on the highway over 35 mph (if I recall correctly) for a time in order to trigger this. Then pass judgement on your situation.
There still could be other issues and it is possible that your O2 sensors may not be performing well. -> But you still haven't run through the free stuff to try, yet.
There still could be other issues and it is possible that your O2 sensors may not be performing well. -> But you still haven't run through the free stuff to try, yet.
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1st thing I would do is replace the fuel filter then test the fuel pressure, Should be above 55psi at all times. Then test the 02's, its important you have proper fuel pressure because the PCM does not monitor the fuel pressure but it does use the sensors to calculate fuel mixture. If the pressure is wrong it throws everything off.
Thread Starter
Teching In
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1st thing I would do is replace the fuel filter then test the fuel pressure, Should be above 55psi at all times. Then test the 02's, its important you have proper fuel pressure because the PCM does not monitor the fuel pressure but it does use the sensors to calculate fuel mixture. If the pressure is wrong it throws everything off.
hey thanks for the advice. I haven't had much time this weekend. I'll tape a gauge on the glass and check it tomorrow. This issue is very easy to duplicate. So I'll rule that out at least. The fuel pump was replaced recently by a dealer.
it's just blowing my mind that if I unplug the MAF the car doesn't exhibit the problem. This simple fact should rule out fuel and spark as far as I can imagine.
i'm tempted to exchange my new MAF and try another one. I cleaned my original MAF with alcohol really well and tried it again but same problem.
i'm starting to lean towards a bad tune. There's a badass ls tuner in my area, I might take it to him. I want to exhaust other possibilities first, though.
With the MAF plugged in the car runs like a top from idle to 2500 rpm and from 3000 up when driving normal. Runs like a top at WOT. Just bogs at medium load between 2500-3000 rpm in all gears.
Unplug the maf and the car drives great at all loads, rpm, and speeds.
Last edited by jshow816; Jul 28, 2018 at 09:28 PM.
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I don't know what tables it defaults to when the maf is unplugged but I'm going to guess speed density and without looking into this I'm not sure how the 02s are used in that mode. I think If it were my car 1st thing I would do AFTER checking the fuel pressure is reseat ALL the engine sensor connections including the PCM. While back I bought a 15 year old WS6 that was doing odd things and after a bunch of fooling around with the dealer I dug into it and found the connections at the PCM under the hood were slightly dirty-oxidized. I took the connectors off the pcm and cleaned all the pins carefully then lightly sprayed them with electrical lubricant, All the weirdness disappeared. Not saying this is your trouble but it could be a connection at the maf or etc. Good Luck
I always start with fuel pressure tests 1st because its the one thing that can effect everything. After fuel I'd check the 02s carefully.
I always start with fuel pressure tests 1st because its the one thing that can effect everything. After fuel I'd check the 02s carefully.
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From: Schiller Park, ILL Member: #317
Checking fuel pressure is never a bad idea, so you can certainly add that to your "to do" list, but based on the fact that WOT feels fine it's not likely a fuel pressure issue (although, since the car is new to you, it might be missing WOT power that you don't even realize it's missing - so, yes, a fuel pressure check is definitely a good idea in this case, just to rule it out.)
I wonder if there is a wiring issue causing minor corruption of the MAF signal (either not bad enough to set an SES, or the code has been disabled)? That could explain why a replacement unit isn't helping, and also why there are no issues when in SD mode. Or, like you mentioned, there is the wild card of having an unknown aftermarket tune. No telling what all was done during the tune, and/or how well it was done, and/or what sort of issues they might have tried to resolve/cover up rather than properly repair. Perhaps the issue lies there, as you suggest.
I wonder if there is a wiring issue causing minor corruption of the MAF signal (either not bad enough to set an SES, or the code has been disabled)? That could explain why a replacement unit isn't helping, and also why there are no issues when in SD mode. Or, like you mentioned, there is the wild card of having an unknown aftermarket tune. No telling what all was done during the tune, and/or how well it was done, and/or what sort of issues they might have tried to resolve/cover up rather than properly repair. Perhaps the issue lies there, as you suggest.
Thread Starter
Teching In
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Checking fuel pressure is never a bad idea, so you can certainly add that to your "to do" list, but based on the fact that WOT feels fine it's not likely a fuel pressure issue (although, since the car is new to you, it might be missing WOT power that you don't even realize it's missing - so, yes, a fuel pressure check is definitely a good idea in this case, just to rule it out.)
I wonder if there is a wiring issue causing minor corruption of the MAF signal (either not bad enough to set an SES, or the code has been disabled)? That could explain why a replacement unit isn't helping, and also why there are no issues when in SD mode. Or, like you mentioned, there is the wild card of having an unknown aftermarket tune. No telling what all was done during the tune, and/or how well it was done, and/or what sort of issues they might have tried to resolve/cover up rather than properly repair. Perhaps the issue lies there, as you suggest.
I wonder if there is a wiring issue causing minor corruption of the MAF signal (either not bad enough to set an SES, or the code has been disabled)? That could explain why a replacement unit isn't helping, and also why there are no issues when in SD mode. Or, like you mentioned, there is the wild card of having an unknown aftermarket tune. No telling what all was done during the tune, and/or how well it was done, and/or what sort of issues they might have tried to resolve/cover up rather than properly repair. Perhaps the issue lies there, as you suggest.
When the MAF is unplugged it does set p0102, so that code is there. The car is in incredible shape for its age, it has been really well cared for and its obvious. The problem is the previous owner's teenage son drove the car over the last year, and that is who performed the EGR & AIR delete and put on the K&N FIPK intake. The kid's friend is who subsequently "tuned" the car. I asked what was tuned and he told me the codes for the deletes were removed, and they changed the fueling and "some other things".
Is there any cost effective way to at least pull and view the tune?
Joined: Nov 2001
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From: Schiller Park, ILL Member: #317
If you don't have any sort of tuning/comprehensive scanning software yourself, there really aren't any options here other than getting another tuner to look at it, or getting a reflash to stock.
Thread Starter
Teching In
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Definitely could be a problem and not the tune.
I'm working today and I drove the Trans Am without the MAF plugged in and it drives almost perfect. Not as much power as when the MAF is plugged in, and the shifts are harsher, but it pulls solidly through the troublesome RPM range at partial throttle.
I'll check the fuel pressure and inspect some wiring this afternoon if I have time and report back.
I'm working today and I drove the Trans Am without the MAF plugged in and it drives almost perfect. Not as much power as when the MAF is plugged in, and the shifts are harsher, but it pulls solidly through the troublesome RPM range at partial throttle.
I'll check the fuel pressure and inspect some wiring this afternoon if I have time and report back.
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REALLY.....didn't someone try to tell you it was NOT the MAF.....and that unplugging it is ABSOLUTELY NOT a good way to test that.
Let us all know when you go get a scan with a REAL OBDII scanner with the engine running and tell us how the 02 sensors are switching. And make sure the person reading the scanner has a LOT of experience and knows how to read the switching.......as I mentioned in an earlier post. Most dealerships cost about $25.00 for that scan.
Stop spending money until you confirm its NOT the 02 sensor(s). Or keep trying to find the needle in a hay stack..... you will definitely find it at some point.
LONG experience with these cars......your symptoms are EXACTLY that. Not saying it can't be something else or a combination of more than one item failing, because these PCMs, sensors and wiring harnesses are pretty damn complex. Nobody has them all figured out. You're not even getting a code to tell you where to look, that proves that these PCM's cannot do it all.
There's not a single electrical engineer at GM that can tell you whats wrong with your car, not the people who designed the system or the people who built it. Technicians at dealerships, are basically idiots when it comes to these systems. You have to rely on forums like this and the people who have had all these weird *** issues.
Good luck.
((((I'm only going off of your symptoms.......and nothing else))))
.
Let us all know when you go get a scan with a REAL OBDII scanner with the engine running and tell us how the 02 sensors are switching. And make sure the person reading the scanner has a LOT of experience and knows how to read the switching.......as I mentioned in an earlier post. Most dealerships cost about $25.00 for that scan.
Stop spending money until you confirm its NOT the 02 sensor(s). Or keep trying to find the needle in a hay stack..... you will definitely find it at some point.
Please explain how o2 sensors could be the culprit here? It is my understanding they would still be doing the same job with or without the MAF sensor plugged in, so I would expect to see the issue still?
There's not a single electrical engineer at GM that can tell you whats wrong with your car, not the people who designed the system or the people who built it. Technicians at dealerships, are basically idiots when it comes to these systems. You have to rely on forums like this and the people who have had all these weird *** issues.
Good luck.
((((I'm only going off of your symptoms.......and nothing else))))
.
Thread Starter
Teching In
Joined: May 2018
Posts: 26
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REALLY.....didn't someone try to tell you it was NOT the MAF.....and that unplugging it is ABSOLUTELY NOT a good way to test that.
Let us all know when you go get a scan with a REAL OBDII scanner with the engine running and tell us how the 02 sensors are switching. And make sure the person reading the scanner has a LOT of experience and knows how to read the switching.......as I mentioned in an earlier post. Most dealerships cost about $25.00 for that scan.
Stop spending money until you confirm its NOT the 02 sensor(s). Or keep trying to find the needle in a hay stack..... you will definitely find it at some point.
LONG experience with these cars......your symptoms are EXACTLY that. Not saying it can't be something else or a combination of more than one item failing, because these PCMs, sensors and wiring harnesses are pretty damn complex. Nobody has them all figured out. You're not even getting a code to tell you where to look, that proves that these PCM's cannot do it all.
There's not a single electrical engineer at GM that can tell you whats wrong with your car, not the people who designed the system or the people who built it. Technicians at dealerships, are basically idiots when it comes to these systems. You have to rely on forums like this and the people who have had all these weird *** issues.
Good luck.
((((I'm only going off of your symptoms.......and nothing else))))
.
Let us all know when you go get a scan with a REAL OBDII scanner with the engine running and tell us how the 02 sensors are switching. And make sure the person reading the scanner has a LOT of experience and knows how to read the switching.......as I mentioned in an earlier post. Most dealerships cost about $25.00 for that scan.
Stop spending money until you confirm its NOT the 02 sensor(s). Or keep trying to find the needle in a hay stack..... you will definitely find it at some point.
LONG experience with these cars......your symptoms are EXACTLY that. Not saying it can't be something else or a combination of more than one item failing, because these PCMs, sensors and wiring harnesses are pretty damn complex. Nobody has them all figured out. You're not even getting a code to tell you where to look, that proves that these PCM's cannot do it all.
There's not a single electrical engineer at GM that can tell you whats wrong with your car, not the people who designed the system or the people who built it. Technicians at dealerships, are basically idiots when it comes to these systems. You have to rely on forums like this and the people who have had all these weird *** issues.
Good luck.
((((I'm only going off of your symptoms.......and nothing else))))
.
I'm trying to use some common sense and NOT waste money. When the MAF is unplugged, doesn't the car use a combination of MAP and o2 readings to determine fueling? So if the o2's were bad, wouldn't I continue seeing some issues when the MAF is unplugged if the o2's were bad? I'm not dismissing your contribution, and I appreciate your effort here. I've not had time this weekend to work on this.
I have to take the car in for a state inspection this week so I can get it registered. I'll ask the shop to take a look at the o2's while it is there. Should I ask them to look for anything specifically since its not throwing codes? Just to check how quickly they're switching?
Thread Starter
Teching In
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All I know if a couple of young teenagers monkeyed around with the tune. Who knows what they might have altered. Codes may have been deleted that do relate to o2 or something.
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From: Schiller Park, ILL Member: #317
I read 50 threads where people's cars had similar issues at between 2k - 3k rpm. THEY reported when they unplugged the MAF the car ran better. Then came back and reported after replacement of the MAF the car was fixed. I am attempting to utilize the wealth of knowledge here, unfortunately I did not get lucky.
I'm trying to use some common sense and NOT waste money. When the MAF is unplugged, doesn't the car use a combination of MAP and o2 readings to determine fueling? So if the o2's were bad, wouldn't I continue seeing some issues when the MAF is unplugged if the o2's were bad?
+1. It's still too early to pat ourselves on the back for making a guess; particularly when it hasn't proven to be true yet.
That being said, we are all making guesses in the interest of economics. The MAF clearly had a problem since it had visible oiling, but it seems to only be part of the issue.
We have had (a small few) folks with the MAF issue also have O2 problems at the same time. Replacing these is a little bit pricey as they should have 20-70K miles left on them - but they could be it. Switching isn't everything. Bad sensors can switch but not sense the proper oxygen concentration in the exhaust. If this route is chosen, not all money would be lost if the O2's prove not to be the problem, either. Since the existing sensors (at best) might have a partial life, only partial value would be lost.
The tune is also an interesting route to explore. Unless a friend can be found with the tools, I expect this might be more expensive than getting a fuel gauge and trying the O2's.
That being said, we are all making guesses in the interest of economics. The MAF clearly had a problem since it had visible oiling, but it seems to only be part of the issue.
We have had (a small few) folks with the MAF issue also have O2 problems at the same time. Replacing these is a little bit pricey as they should have 20-70K miles left on them - but they could be it. Switching isn't everything. Bad sensors can switch but not sense the proper oxygen concentration in the exhaust. If this route is chosen, not all money would be lost if the O2's prove not to be the problem, either. Since the existing sensors (at best) might have a partial life, only partial value would be lost.
The tune is also an interesting route to explore. Unless a friend can be found with the tools, I expect this might be more expensive than getting a fuel gauge and trying the O2's.
Thread Starter
Teching In
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Welp everyone PROBLEM SOLVED.
I checked the fuel pressure and it was good. Picked up another MAF from a scrapper and had same problem.
I went ahead and decided to take it to have the tune checked. And that was it. The tuner said the MAF curve was jagged instead of smooth. He said the ve table was pretty good which explained why it ran SO much better with the sensor unplugged.
Anyways the first dyno run with the crap tune the car made a whopping 236 whp. Tuning got it to 287 whp. Not bad for a 20 year old stock ls1.
Now time for bolt ons!
Big thanks to KC Maxx Performance. Great shop.
I checked the fuel pressure and it was good. Picked up another MAF from a scrapper and had same problem.
I went ahead and decided to take it to have the tune checked. And that was it. The tuner said the MAF curve was jagged instead of smooth. He said the ve table was pretty good which explained why it ran SO much better with the sensor unplugged.
Anyways the first dyno run with the crap tune the car made a whopping 236 whp. Tuning got it to 287 whp. Not bad for a 20 year old stock ls1.
Now time for bolt ons!
Big thanks to KC Maxx Performance. Great shop.
Those numbers sound good. Enjoy your new ride!
