Alot of hesitation / light thuds under medium and hard accelleration [UPDATE: Solved]
08-28-2017, 07:29 AM
#1
Alot of hesitation / light thuds under medium and hard accelleration [UPDATE: Solved] 99 Z28, 210K miles.
I can't tell if its mis-firing or if the torque converter / trans is slipping. Basically, especially from a dig when I hit the gas hard the RPMS climb up to about 1.5k then it will just fluctuate between 1.5k to 2.5k like its stumbling and doesn't want to climb past that area but its not backfiring it just has an area of the RPM band where it seems to be having difficulties. After it finally gets past 2.5k it launches and there's light thuds going through the car.
I was wondering if it was something as simple as a bad MAF, or something as complicated as a torque converter / transmission problem?
I can't tell if its mis-firing or if the torque converter / trans is slipping. Basically, especially from a dig when I hit the gas hard the RPMS climb up to about 1.5k then it will just fluctuate between 1.5k to 2.5k like its stumbling and doesn't want to climb past that area but its not backfiring it just has an area of the RPM band where it seems to be having difficulties. After it finally gets past 2.5k it launches and there's light thuds going through the car.
I was wondering if it was something as simple as a bad MAF, or something as complicated as a torque converter / transmission problem?
Last edited by Need4Camaro; 03-08-2018 at 04:50 PM.
08-30-2017, 06:28 AM
#4
It sounds like something you'd really need a scanner to diagnose with someone in the passenger's seat looking at real-time data.
You might also try taking the MAF out of the equation by unplugging it. You'll probably get some codes by doing that, but it should revert back to alternate methods of calculating fuel/air ratios. If the problem goes away, you'll at least know it's not a transmission problem, etc.
Unplugging the MAF won't confirm if the problem is indeed the MAF, but it will help you zero in on things in absence of a live data scanner.
You might also try taking the MAF out of the equation by unplugging it. You'll probably get some codes by doing that, but it should revert back to alternate methods of calculating fuel/air ratios. If the problem goes away, you'll at least know it's not a transmission problem, etc.
Unplugging the MAF won't confirm if the problem is indeed the MAF, but it will help you zero in on things in absence of a live data scanner.
02-12-2018, 05:55 AM
#5
Sorry for the late replies here. Although it was true I did have a slipping transmission and I replaced with a FLT Level 6 model (curing all slippage and gave me an awesome transmission) ...The issue remains and still occurs at around 2 to 2.5k RPMs... It appears I may ALSO have an issue with the MAF. I unplugged it and took it out and it drove 100% normal and absolutely no hesitation when accelerating. So I believe it is the MAF.
With that stated, do you think MAF cleaner will still help or should I just go ahead and replace it? Also which MAF would you recommend? I'm using a truck MAF from eBay right now and it was brand new.. Truck MAF's have a bigger opening but should I go back to an F-Body MAF and does anyone know the correct PN for a 99 Z28?
With that stated, do you think MAF cleaner will still help or should I just go ahead and replace it? Also which MAF would you recommend? I'm using a truck MAF from eBay right now and it was brand new.. Truck MAF's have a bigger opening but should I go back to an F-Body MAF and does anyone know the correct PN for a 99 Z28?
02-12-2018, 01:30 PM
#7
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You mentioned using a truck MAF....was this a GM part? I'm not familiar with all the truck units and if their calibration is different enough to cause these issues. Did it ever work correctly when first installed? If so, then perhaps a cleaning might help, but if you've always used a paper filter and your lid seals up well, it's probably not going to be that dirty. Might just be a cheap part, etc. Is the MAF harness and connector in good shape? Sounds like either the unit has failed in some way, or the signal is poor.
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02-12-2018, 11:56 PM
#8
I agree. There is no point in looking at other causes if unplugging the MAF cures the condition completely. This is what should be focused on.
You mentioned using a truck MAF....was this a GM part? I'm not familiar with all the truck units and if their calibration is different enough to cause these issues. Did it ever work correctly when first installed? If so, then perhaps a cleaning might help, but if you've always used a paper filter and your lid seals up well, it's probably not going to be that dirty. Might just be a cheap part, etc. Is the MAF harness and connector in good shape? Sounds like either the unit has failed in some way, or the signal is poor.
You mentioned using a truck MAF....was this a GM part? I'm not familiar with all the truck units and if their calibration is different enough to cause these issues. Did it ever work correctly when first installed? If so, then perhaps a cleaning might help, but if you've always used a paper filter and your lid seals up well, it's probably not going to be that dirty. Might just be a cheap part, etc. Is the MAF harness and connector in good shape? Sounds like either the unit has failed in some way, or the signal is poor.
When I first put it in, I don't "think" there were any problems.. but the problems are kind of odd to begin with because it doesn't always do it, it does it alot more than it used to though. But I noticed especially when its cold outside it drives perfectly normal and I installed it around last winter I believe.
02-13-2018, 12:02 AM
#9
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Yeah, still using the stock cats, been holding out till I do the exhaust but I wouldn't be surprised if one of them is failing by now at 211k miles
The MAF is a GM part but what originally happened and how I found out it was a truck MAF was after receiving it, it was just SLIGHTLY larger than my stock MAF and would NOT go into my LID force, push, pry, nothing... after heating my lid with a heatgun and just forcing it in there it finally took but I knew it was the wrong part from the start which is why I've been concerned about it..
When I first put it in, I don't "think" there were any problems.. but the problems are kind of odd to begin with because it doesn't always do it, it does it alot more than it used to though. But I noticed especially when its cold outside it drives perfectly normal and I installed it around last winter I believe.
The MAF is a GM part but what originally happened and how I found out it was a truck MAF was after receiving it, it was just SLIGHTLY larger than my stock MAF and would NOT go into my LID force, push, pry, nothing... after heating my lid with a heatgun and just forcing it in there it finally took but I knew it was the wrong part from the start which is why I've been concerned about it..
When I first put it in, I don't "think" there were any problems.. but the problems are kind of odd to begin with because it doesn't always do it, it does it alot more than it used to though. But I noticed especially when its cold outside it drives perfectly normal and I installed it around last winter I believe.
02-13-2018, 01:57 PM
#10
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Yeah, still using the stock cats, been holding out till I do the exhaust but I wouldn't be surprised if one of them is failing by now at 211k miles
The MAF is a GM part but what originally happened and how I found out it was a truck MAF was after receiving it, it was just SLIGHTLY larger than my stock MAF and would NOT go into my LID force, push, pry, nothing... after heating my lid with a heatgun and just forcing it in there it finally took but I knew it was the wrong part from the start which is why I've been concerned about it..
When I first put it in, I don't "think" there were any problems.. but the problems are kind of odd to begin with because it doesn't always do it, it does it alot more than it used to though. But I noticed especially when its cold outside it drives perfectly normal and I installed it around last winter I believe.
The MAF is a GM part but what originally happened and how I found out it was a truck MAF was after receiving it, it was just SLIGHTLY larger than my stock MAF and would NOT go into my LID force, push, pry, nothing... after heating my lid with a heatgun and just forcing it in there it finally took but I knew it was the wrong part from the start which is why I've been concerned about it..
When I first put it in, I don't "think" there were any problems.. but the problems are kind of odd to begin with because it doesn't always do it, it does it alot more than it used to though. But I noticed especially when its cold outside it drives perfectly normal and I installed it around last winter I believe.
I agree with the above; something is either off with tune calibration for this MAF in this application, or it's just a faulty/cheap and/or failing MAF.
02-27-2018, 01:33 AM
#11
Im looking into replacing my MAF now... probably making this harder than it is but just want to get a few opinions before I pull the trigger...
This is the MAF I originally got on eBay:
https://www.ebay.com/itm/New-Mass-Ai...item3f678f380a
Although it physically connects and works Im not sure if it will work properly with the F-Body. one thing I like about it is it has a larger diameter thus logically should flow more. Should I try to have my current MAF tuned first? or is this plainly incompatible and I should look for an F-Body MAF?
If I get an F-Body MAF, can I use those unscreened ported MAF ends? I tried this once on my stock MAF (over 200k miles on the stock MAF) and immediately got an SES, so I dont know if it was the MAF or the lack of a screen... but which route should I take first?
Edit:
I'm looking into other MAF's and running into a bit of confusion.
I am believing the MAF I have on there now is probably an 85mm Truck MAF and it was never tuned. I am thinking that is whats wrong.
I've been researching and it sounds like its no longer possible to get the stock MAF... If Im wrong though, If I were to get a stock MAF, would I see any benefit from a ported de-screened stock MAF over a Truck MAF? or should I just try to get the Truck MAF tuned? or should I try to get a Delco Stock MAF? I have large power goals for the future so I dont know if running the stock one would be ideal.
This is the MAF I originally got on eBay:
https://www.ebay.com/itm/New-Mass-Ai...item3f678f380a
Although it physically connects and works Im not sure if it will work properly with the F-Body. one thing I like about it is it has a larger diameter thus logically should flow more. Should I try to have my current MAF tuned first? or is this plainly incompatible and I should look for an F-Body MAF?
If I get an F-Body MAF, can I use those unscreened ported MAF ends? I tried this once on my stock MAF (over 200k miles on the stock MAF) and immediately got an SES, so I dont know if it was the MAF or the lack of a screen... but which route should I take first?
Edit:
I'm looking into other MAF's and running into a bit of confusion.
I am believing the MAF I have on there now is probably an 85mm Truck MAF and it was never tuned. I am thinking that is whats wrong.
I've been researching and it sounds like its no longer possible to get the stock MAF... If Im wrong though, If I were to get a stock MAF, would I see any benefit from a ported de-screened stock MAF over a Truck MAF? or should I just try to get the Truck MAF tuned? or should I try to get a Delco Stock MAF? I have large power goals for the future so I dont know if running the stock one would be ideal.
Last edited by Need4Camaro; 02-27-2018 at 08:38 AM.
02-27-2018, 02:57 PM
#12
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I do recall there being an update to the "stock" MAF from GM several years ago. But, as far as I know, these updated/redesigned (or perhaps borrowed from a compatible platform?) units are still available. I've never used one personally, so I can't 100% speak to their performance, but I also don't recall seeing any complaints. From what I recall, there is a physical appearance difference, and perhaps an adapter? I haven't needed one, nor seen pictures of one in quite some time so I don't remember exactly.
Having said that, I wouldn't do anything to modify any application-proper MAF at first. Just see how it performs, and if it solves all your problems before messing with it. But, I do understand that you're planning a serious build, so a stock-size MAF might not be ideal for your eventual application. You might also consider a speed density tune for your future build if you feel that the MAF will be a restriction.
Having said that, I wouldn't do anything to modify any application-proper MAF at first. Just see how it performs, and if it solves all your problems before messing with it. But, I do understand that you're planning a serious build, so a stock-size MAF might not be ideal for your eventual application. You might also consider a speed density tune for your future build if you feel that the MAF will be a restriction.
02-27-2018, 03:09 PM
#13
I do recall there being an update to the "stock" MAF from GM several years ago. But, as far as I know, these updated/redesigned (or perhaps borrowed from a compatible platform?) units are still available. I've never used one personally, so I can't 100% speak to their performance, but I also don't recall seeing any complaints. From what I recall, there is a physical appearance difference, and perhaps an adapter? I haven't needed one, nor seen pictures of one in quite some time so I don't remember exactly.
Having said that, I wouldn't do anything to modify any application-proper MAF at first. Just see how it performs, and if it solves all your problems before messing with it. But, I do understand that you're planning a serious build, so a stock-size MAF might not be ideal for your eventual application. You might also consider a speed density tune for your future build if you feel that the MAF will be a restriction.
Having said that, I wouldn't do anything to modify any application-proper MAF at first. Just see how it performs, and if it solves all your problems before messing with it. But, I do understand that you're planning a serious build, so a stock-size MAF might not be ideal for your eventual application. You might also consider a speed density tune for your future build if you feel that the MAF will be a restriction.
02-27-2018, 03:36 PM
#14
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I have no experience with that brand, so I really can't offer advice on its quality one way or the other.
02-27-2018, 05:24 PM
#16
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Personally, if this is a street car, keep the MAF, but at least upgrade to a 100mm one from TSP. This will leave you room to grow. If your power goals are beyond say about 700 rwhp, then MAF is probably not for you, as you will hit the Hertz limit, even with scaling the tune. Speed density can be fine for the street, but MAF is always going to get you the optimal performance in every condition. SD... Not so much, depending on the tune. Great for the track and huge power though.
If you are planning on SD, then you don't even need to buy a MAF. You can straight up delete it. Food for thought.
If your aspirations are not that high, as in all out racecar, then I'd stick with a larger aftermarket MAF, like the TSP model. I have one on my 98, though I have yet to enable it. It does work though, with adapter. Haven't had a lot of time to work on my tune lately, and since I've had it back together I've been running it in speed density. I actually had to swap my PCM so it would be fast enough to accommodate the larger MAF, and 427 stroker. It has a little bit "different" fueling needs over the LS1.
If you are planning on SD, then you don't even need to buy a MAF. You can straight up delete it. Food for thought.
If your aspirations are not that high, as in all out racecar, then I'd stick with a larger aftermarket MAF, like the TSP model. I have one on my 98, though I have yet to enable it. It does work though, with adapter. Haven't had a lot of time to work on my tune lately, and since I've had it back together I've been running it in speed density. I actually had to swap my PCM so it would be fast enough to accommodate the larger MAF, and 427 stroker. It has a little bit "different" fueling needs over the LS1.
02-27-2018, 05:28 PM
#17
TECH Fanatic
I should also mention, I had the 98 computer in there too. It was old and tired, and simply just a PITA to tune. I have an 0411 with the latest OS and everything has gotten SO much easier to tune. I do plan on running MAF since I can easily scale the tune down to meet my needs. I'm only in the 500-550 rwhp range though.
02-27-2018, 10:55 PM
#18
I should also mention, I had the 98 computer in there too. It was old and tired, and simply just a PITA to tune. I have an 0411 with the latest OS and everything has gotten SO much easier to tune. I do plan on running MAF since I can easily scale the tune down to meet my needs. I'm only in the 500-550 rwhp range though.
02-28-2018, 01:24 AM
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There's a ton of searchable info on SD tunes and how they have performed for many folks vs. an MAF. Lots of reading on this topic, take some time to research this (if you haven't already) before making any decisions.
02-28-2018, 02:07 PM
#20
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