Newly aquired 993 stumbles, bucks, and backfires under load at half to full throttle
04-16-2008, 07:00 PM
#32
Going back to the simple things...
Did the problem occur immediately after the air filter change? If so, I would do two things:
1. Remove the filter and drive the car to see if the problem persists. I have read of filters "collapsing" under vacuum pressure from the intake manifold. I think this was mostly limited to aftermarket airboxes without sufficient clamping force to hold the filter in place. This would potentially cause the stumbling/loss of power.
2. Check all hoses/wiring going to the MAF and surrounding area to ensure something wasn't bumped or pulled loose during the filter install. If the car ran well after the change and then developed the problem shortly after, this could still be the problem.
Did the problem occur immediately after the air filter change? If so, I would do two things:
1. Remove the filter and drive the car to see if the problem persists. I have read of filters "collapsing" under vacuum pressure from the intake manifold. I think this was mostly limited to aftermarket airboxes without sufficient clamping force to hold the filter in place. This would potentially cause the stumbling/loss of power.
2. Check all hoses/wiring going to the MAF and surrounding area to ensure something wasn't bumped or pulled loose during the filter install. If the car ran well after the change and then developed the problem shortly after, this could still be the problem.
04-16-2008, 07:48 PM
#33
Drifting
Oil from the K&N can foul the MAF sensor. Remove it to clean it, not too hard and give it a good spraying. I have been told once it messes up the sensor, replacement is necessary. Maybe you could borrow one from another car to test before spending $ if cleaning doesn't do it.
04-16-2008, 11:05 PM
#35
WOOOHOOOO! EUREKA! The MAF sensor it was. I took it out and sprayed it down with the CRC MAF cleaner according to their directions and it runs awesome now!
I'm thinking that when I removed and replaced that K&N with the paper filter, some dust/dirt must have dislodged from the K&N as I was removing it and then got sucked into the MAF contaminating it. These filters are popular as my other 993 has a K&N also. I replaced the one on my new 993 with a paper one due to all the controversy about them...perhaps the naysayers are right.
Can't wait to hit the 190 this weekend...such a fast diagnosis would not have been possible if not for Rennlist. THANKS TO ALL...the $32 I spent for 2 years membership is the best money I've ever invested!!!
Replace that white truck on the 190 with my blue 993 and you'll get the picture.
I'm thinking that when I removed and replaced that K&N with the paper filter, some dust/dirt must have dislodged from the K&N as I was removing it and then got sucked into the MAF contaminating it. These filters are popular as my other 993 has a K&N also. I replaced the one on my new 993 with a paper one due to all the controversy about them...perhaps the naysayers are right.
Can't wait to hit the 190 this weekend...such a fast diagnosis would not have been possible if not for Rennlist. THANKS TO ALL...the $32 I spent for 2 years membership is the best money I've ever invested!!!
Replace that white truck on the 190 with my blue 993 and you'll get the picture.
Last edited by midnite993; 08-13-2010 at 09:12 PM.
04-17-2008, 09:36 AM
#38
Rennlist Member
There were several theories offered up as to the cause of this problem...Only one was correct...It would be great if someone with the technical knowledge would conduct an "after action review" on this thread and post an appropriate sequence of diagnostic tasks for this type of problem....Kind of like: Start with A. If "Yes" then go to B. If "No" then go to C....The result could be published as a "Here's How You Diagnose Stumbling on Acceleration DIY."
04-17-2008, 10:20 AM
#40
Rennlist Member
There were several theories offered up as to the cause of this problem...Only one was correct...It would be great if someone with the technical knowledge would conduct an "after action review" on this thread and post an appropriate sequence of diagnostic tasks for this type of problem....Kind of like: Start with A. If "Yes" then go to B. If "No" then go to C....The result could be published as a "Here's How You Diagnose Stumbling on Acceleration DIY."
You are right, only one was correct, but if all had read this phrase before, how many would have had it correct? not me, I really was thinking fuel
I'm thinking that when I removed and replaced that K&N with the paper filter, some dust/dirt must have dislodged from the K&N as I was removing it and then got sucked into the MAF contaminating it..
04-17-2008, 11:02 AM
#41
Yes, there was only one correct answer, but it could very well have been any one of the answers! Technically, it was a fuel issue because the MAF was telling the fuel system to flood the engine. Lots of possibilities.
What a great idea though for a DIY article. I think I could write up a pretty good DIY on this (I write computer instruction manuals), then submit it to the board for changes, mistakes, and additions. If I did that do you think someone like Robin or Pcarworkshop.com would post it?
What a great idea though for a DIY article. I think I could write up a pretty good DIY on this (I write computer instruction manuals), then submit it to the board for changes, mistakes, and additions. If I did that do you think someone like Robin or Pcarworkshop.com would post it?
04-17-2008, 11:04 AM
#42
Race Director
My M5 and my Miata both had the stumbling symptoms. I was thinking fuel in both cases, so much so that I actually changed the fuel pump in the Miata. Did nothing.
The M5borad is full of threads on MAF failures, and that was indeed the cause of my car problems, both M5 and Miata. We normally don't associate MAF as a maintenence item, but now it's ingrained in my brain that stumbling could possibly be caused by MAF issues. That does make sense as the MAF actually tells the computer how much fuel to send based on how much air it 'perceives' is flowing. Thus a sputtering MAF could cause the ECU to direct sputtering fuel delivery, and engine stumbles.
Just my 2 cents. In any case, just glad he solved the problems.
CP
The M5borad is full of threads on MAF failures, and that was indeed the cause of my car problems, both M5 and Miata. We normally don't associate MAF as a maintenence item, but now it's ingrained in my brain that stumbling could possibly be caused by MAF issues. That does make sense as the MAF actually tells the computer how much fuel to send based on how much air it 'perceives' is flowing. Thus a sputtering MAF could cause the ECU to direct sputtering fuel delivery, and engine stumbles.
Just my 2 cents. In any case, just glad he solved the problems.
CP
04-17-2008, 11:48 AM
#43
Rennlist Member
Please understand that I wasn't being critical of anyone's suggestions. As far as I know, they were all valid possibilities. At the same time, I'm sure that some were more possible, or perhaps more likely, than others.
I was just hoping that someone who had the knowledge to do so could develop a "sequential task analysis" of how to go through the process of troubleshooting the problem, moving from the simplest, most likely possibilites to the more complex and/or less likely.
We have access to a lot of DIYs. The problem is the DIYs do not always explain how to know when it is necessary to DIY.
It seems to me that would be nice to develop a similar set of "Troubleshooting Sequences" so that we could systematically and methodically go through a process that would lead us to the proper solution in the least amount of time and the highest probability of accuracy.
I once knew a master mechanic who distinguished between a mechanic and a "parts hanger." According to him, a mechanic used common sense and vaild troubleshooting sequences to isolate and repair any given problem. "Parts hangers" just start putting new parts on until the problem goes away.
I'd like to be more of a mechanic than a parts hanger and thought that troubleshooting sequences might be an answer.
Again, no disrespect intended.
Regards,
Terry
I was just hoping that someone who had the knowledge to do so could develop a "sequential task analysis" of how to go through the process of troubleshooting the problem, moving from the simplest, most likely possibilites to the more complex and/or less likely.
We have access to a lot of DIYs. The problem is the DIYs do not always explain how to know when it is necessary to DIY.
It seems to me that would be nice to develop a similar set of "Troubleshooting Sequences" so that we could systematically and methodically go through a process that would lead us to the proper solution in the least amount of time and the highest probability of accuracy.
I once knew a master mechanic who distinguished between a mechanic and a "parts hanger." According to him, a mechanic used common sense and vaild troubleshooting sequences to isolate and repair any given problem. "Parts hangers" just start putting new parts on until the problem goes away.
I'd like to be more of a mechanic than a parts hanger and thought that troubleshooting sequences might be an answer.
Again, no disrespect intended.
Regards,
Terry
04-17-2008, 12:17 PM
#44
Rennlist Member
...I was just hoping that someone who had the knowledge to do so could develop a "sequential task analysis" of how to go through the process of troubleshooting the problem,
...
I once knew a master mechanic who distinguished between a mechanic and a "parts hanger." According to him, a mechanic used common sense and vaild troubleshooting sequences to isolate and repair any given problem. "Parts hangers" just start putting new parts on until the problem goes away.
...
...
I once knew a master mechanic who distinguished between a mechanic and a "parts hanger." According to him, a mechanic used common sense and vaild troubleshooting sequences to isolate and repair any given problem. "Parts hangers" just start putting new parts on until the problem goes away.
...
(1) how easy is it to do, and
(2) how likely is it to solve the problem.
Here, the OP (a) asked us what tests were available and might solve the problem, then (b) started with the easiest one (clean the MAF) and fortunately it worked. The workshop manuals have a nice matrix of problems with symptoms, but cleaning the MAF isn't on it!
04-17-2008, 12:40 PM
#45
Drifting
Ditto X 1000 on the multiple 'possibilities' piece...
Yes, there was only one correct answer, but it could very well have been any one of the answers! Technically, it was a fuel issue because the MAF was telling the fuel system to flood the engine. Lots of possibilities.
What a great idea though for a DIY article. I think I could write up a pretty good DIY on this (I write computer instruction manuals), then submit it to the board for changes, mistakes, and additions. If I did that do you think someone like Robin or Pcarworkshop.com would post it?
What a great idea though for a DIY article. I think I could write up a pretty good DIY on this (I write computer instruction manuals), then submit it to the board for changes, mistakes, and additions. If I did that do you think someone like Robin or Pcarworkshop.com would post it?