Hesitation on acceleration
#1
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I'm not normally one to ask questions to the forum since I much prefer lurk/hunt for answers but I've been baffled now for about a week on this one. I've been searching using different tags but haven't come up with a solution to the acceleration problem, or the sticking throttle body.
I'll try to find a way to get datalogs as soon as possible. My tuning laptop is broken :(
Info:
'95 1.8 boosted running on MSExtra 2 so CEL checking isn't possible (not that I know of). Car has been running well up until now and no recent work has been done that would suggest cause for either problem.
Problems:
-Car hesitates/stumbles when throttle is applied. Sometimes dies when I try to come off a light because the RPMs drop so much.
Have already tried:
-Pulled TB and cleaned in and around (I know that wears the bore seal but I'm desperate here)
-Ran the car without boost/intake tract to insure intake blockage was not a problem.
-Fuel pump works, replaced fuel filter.
-Changed plugs (NGK BKR5E11-EGP) and the wires (Duralast) are relatively new and have been working fine for my application, despite the cheap-ness.
-Checked injector o-rings for leaks.
-Car achieves peak boost target (15psi) so vacuum leaks are not suspect. Still possible but hasn't been the case in my previous experience.
-Mechanical timing and spark advance tables.
Have not tried but will, time permitting:
-Checking fuel pressure
Below is a link to a video which shows the symptoms. Sorry about the poor quality.
![](https://www.miataturbo.net/attachments/engine-performance-56/74992-hesitation-acceleration-th_vid_20130422_191742_zps36de9bfe.jpg?dateline=1367109427)
I'm open to any and all suggestions for possible cause, including ones that seem far-fetched. If any more information is needed, please do not hesitate to ask.
Thanks in advance!
I'll try to find a way to get datalogs as soon as possible. My tuning laptop is broken :(
Info:
'95 1.8 boosted running on MSExtra 2 so CEL checking isn't possible (not that I know of). Car has been running well up until now and no recent work has been done that would suggest cause for either problem.
Problems:
-Car hesitates/stumbles when throttle is applied. Sometimes dies when I try to come off a light because the RPMs drop so much.
Have already tried:
-Pulled TB and cleaned in and around (I know that wears the bore seal but I'm desperate here)
-Ran the car without boost/intake tract to insure intake blockage was not a problem.
-Fuel pump works, replaced fuel filter.
-Changed plugs (NGK BKR5E11-EGP) and the wires (Duralast) are relatively new and have been working fine for my application, despite the cheap-ness.
-Checked injector o-rings for leaks.
-Car achieves peak boost target (15psi) so vacuum leaks are not suspect. Still possible but hasn't been the case in my previous experience.
-Mechanical timing and spark advance tables.
Have not tried but will, time permitting:
-Checking fuel pressure
Below is a link to a video which shows the symptoms. Sorry about the poor quality.
![](https://www.miataturbo.net/attachments/engine-performance-56/74992-hesitation-acceleration-th_vid_20130422_191742_zps36de9bfe.jpg?dateline=1367109427)
I'm open to any and all suggestions for possible cause, including ones that seem far-fetched. If any more information is needed, please do not hesitate to ask.
Thanks in advance!
Last edited by Grantofhell; 04-29-2013 at 09:44 AM.
#3
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Similar issue? https://www.miataturbo.net/megasquir...h-wrong-72463/
I checked mechanical timing yesterday, it was fine.
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It has been tuned for many months. This came out of no where a few weeks ago. I hadn't made any changes in the tune and it ran very well. Idle was smooth, AFR's were on/very near target for each cell, etc. Even if the tune is the problem, I've no idea where to start :\ ![Noob](https://www.miataturbo.net/images/smilies/noob.gif)
Yes. It does that from any RPM and at any %TPS, whether I'm already on the throttle or not.
I didn't think so either, but it was worth a look.
I'll get a log as soon as I can. My laptop with which I was initially tuning broke and the repair process on it has been dragged out from long work hours. I'll fix it up today and put logs and the tune up.
![Noob](https://www.miataturbo.net/images/smilies/noob.gif)
This. Or so my limited knowledge tells me...
How does the car react if you are driving down the street in 3rd gear at ~4k-5k rpms and let the car engine brake (no throttle), then give it gas. Does it still want to die or lurch?
I don't think mechanical timing will be the culprit.
How does the car react if you are driving down the street in 3rd gear at ~4k-5k rpms and let the car engine brake (no throttle), then give it gas. Does it still want to die or lurch?
I don't think mechanical timing will be the culprit.
Yes. It does that from any RPM and at any %TPS, whether I'm already on the throttle or not.
I didn't think so either, but it was worth a look.
I'll get a log as soon as I can. My laptop with which I was initially tuning broke and the repair process on it has been dragged out from long work hours. I'll fix it up today and put logs and the tune up.
#9
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i'm horribly ashamed of the tune, but here it is.
Data log of a short drive in the rain today is also attached. Some idling, revs, pulls, and downshifts
%TPS is quite interesting since it goes to well over 100 percent then slowly drops back down..Time for a new TPS or just a calibration?
Data log of a short drive in the rain today is also attached. Some idling, revs, pulls, and downshifts
%TPS is quite interesting since it goes to well over 100 percent then slowly drops back down..Time for a new TPS or just a calibration?
Last edited by Grantofhell; 04-29-2013 at 12:24 PM.
#11
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No, it shoots up to about %160 very quickly.
For some reason, I cannot upload the .MSL. It's under the 4.81MB filesize limit, but will not successfully upload. Any other media host you can think of that I can share this via?
For some reason, I cannot upload the .MSL. It's under the 4.81MB filesize limit, but will not successfully upload. Any other media host you can think of that I can share this via?
#15
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Just a bit of an update.
I tried replacing the coilpack(s) with known good unit(s) and no change. Changed TPS with a known good unit; no change. Pulled the fuel pressure regulator and "tested" it by applying 25mmHg vacuum and the diaphragm did not move. I don't exactly know how the FPR works but I assume the vacuum is modulated by the FPR solenoid which opens/closes the diaphragm to allow more or less flow of fuel return.
However, I did get some more insight (which made me think coilpacks):
It gets considerably worse when it's warm out and the engine is already hot. Applying throttle will stall the car after a while driving. Barely maintains idle either. Pulled the plugs and they were blackened. Tried new ones; no change.
The car goes off the road soon for the boost build. I'm on the fence about fixing it with the engine still in, in case the problem resides after I swap in the built block. As well as for educational purposes if this happens again or to someone else.
I tried replacing the coilpack(s) with known good unit(s) and no change. Changed TPS with a known good unit; no change. Pulled the fuel pressure regulator and "tested" it by applying 25mmHg vacuum and the diaphragm did not move. I don't exactly know how the FPR works but I assume the vacuum is modulated by the FPR solenoid which opens/closes the diaphragm to allow more or less flow of fuel return.
However, I did get some more insight (which made me think coilpacks):
It gets considerably worse when it's warm out and the engine is already hot. Applying throttle will stall the car after a while driving. Barely maintains idle either. Pulled the plugs and they were blackened. Tried new ones; no change.
The car goes off the road soon for the boost build. I'm on the fence about fixing it with the engine still in, in case the problem resides after I swap in the built block. As well as for educational purposes if this happens again or to someone else.
#17
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As an update to this thread, during the process of my new build, I'm inspecting all sensors and mechanical bits to see what the problem was initially.
I found the mechanical timing to be off by two notches (teeth). I checked the mechanical timing while I was having the issue and it was 1 tooth off but I corrected the it. Must have been the idler or tensioner because it jumped again. I should have looked at this earlier because I had this exact problem with my mx-3 GS when I bought it in non-running condition.
I'll still continue to check parts and update findings.
I found the mechanical timing to be off by two notches (teeth). I checked the mechanical timing while I was having the issue and it was 1 tooth off but I corrected the it. Must have been the idler or tensioner because it jumped again. I should have looked at this earlier because I had this exact problem with my mx-3 GS when I bought it in non-running condition.
I'll still continue to check parts and update findings.
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