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Discussion Starter #1
97 HX. Built turbo Z6. Stock EX/Z6 (S40 I think it's called) trans. LSD Motorsports 6puck dragger clutch. eCtune. Been driving a stick for well over 10 years, so it's not driver inability. About 1k miles maybe a little more on the clutch. Had the flywheel resurfaced including step spec before the new clutch went it. The car has been professionally dyno tuned.

Seemingly out of nowhere my car developed an intermittent issue :( A stumble is the best way I can describe it. About 25% of the time when I am at a stop and put the car in first and let the clutch out, the car falls flat on it's face, then bucks hard and then everything is fine. Sometimes it will stumble/buck two or three or four times. It's really embarrassing, to be honest. It seems to happen RIGHT at the moment that the clutch becomes fully engaged. When the stumble happens the check engine light turns on, but when it bucks and recovers, it turns right back off. I tried to get it to do it in second, and I was able to get it to do it once staring from a stop in second so it seems to be gear independent.

I've tried logging the MIL and I can't get anything to come up. It happens very quickly. I even turned my sample rate for data logging to the max, and it still doesn't catch anything. No code is stored either.

I have the check engine light set to be a shift light in eCtune. Along with a rev limiter. I'm going to try disabling the rev limiter to see if maybe I'm having some sort of electrical malfunction and the ECU thinks I'm hitting the rev limiter down there. I'm trying to make a correlation between the check engine light turning on and right back off and this stumble. The stumble feels like what boost/fuel cut feels like. Tonight I'll try the rev limiter thing. Trying to get a jump with other suggestions though.

Has anyone encountered this?
 

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The key may be retrieving the CEL code. Sometimes CEL codes are lost after the engine is turned off, so leave the engine running when the CEL turns on and you check for CEL codes.
 

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The MIL/CEL will come on with no engine power or when it gets close to the point of stalling and that may be why the turn on when bucking.

Could the problem be worn out mounts? If they are bad it will slam the motor all over the place and feel horrible when engaging the clutch. Also if the flywheel was stepped wrong or even re surfaced unevenly it will buck too.
 

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Discussion Starter #5 (Edited)
The flywheel was stepped properly. I double checked the height in the machine shop at work. Myself and a few local buddies have had our flywheels resurfaced at this shop in the past too, with good results. Also, it was fine for the first 1k or so miles. So I don't believe it to be improper step height or poor resurfacing, unless somehow I messed up the flywheel surface in that first 1k miles, but I didn't take it in to boost, varied my RPM's, etc. the general clutch break-in guidelines.

As far as worn out mounts. I replaced all mounts and filled them with 60A urethane when I replaced them. Except for the liquid filled drivers side mount. I replaced that with a billet Innovative mount with a 60A bushing as well. The motor and trans are pretty solid.

Regarding the CEL, good point. I didn't think about the fact that it turns on near the point of the car stalling. I would expect to see the MIL column switch to yes in eCtune or some sort of other abnormality if that happened, but maybe I'm making a poor assumption. One reason that I do not believe this is it, is because when I was trying to determine if it was gear based or not, I put it in second and revved her pretty high, around 2.5k before letting the clutch out realllllly slowly. And the check engine light flashed for a second, just like in first gear, but didn't stumble and buck like it does during normal driving in first gear, because I had the R's up so high. It never dipped below I think about 1.2k (ish) while I was letting it out, but the MIL still made a brief appearance.

What gets me is the intermittent part. The worst problems to try and solve. I'm going to go change my oil and try turning the rev limiter off and seeing what happens. I'm trying to remember exactly when this happened, and it seemed to start shortly after doing a big burnout a week or so ago. I don't know if that is just coincidence, though. Also, I did it very late at night in an abandoned industrial part of the city :)
 

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Regarding the CEL, good point. I didn't think about the fact that it turns on near the point of the car stalling.
You didn't think of it because the whole concept is wrong.

Go stall your engine by popping the clutch. The CEL should not turn on.

Bottom line: If the CEL turns on, there's a trouble code in the ECU. Figure out how to retrieve it. I suggested one way, but there may be others.
 

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Discussion Starter #7 (Edited)
You didn't think of it because the whole concept is wrong.

Go stall your engine by popping the clutch. The CEL should not turn on.

Bottom line: If the CEL turns on, there's a trouble code in the ECU. Figure out how to retrieve it. I suggested one way, but there may be others.
Hey, man, I don't want to start an argument, but that statement is incorrect. eCtune allows me to turn the CEL on for things other than DTC's. So there is the possibility that it can turn on without any trouble code being thrown if there is something causing the ECU to think it is at the rev limiter, or proper RPM for MIL shift light. I'm not saying that this is the case, but that it is a possibility.

Also, I have yet to find a way to retrieve it, because it is :

1) Not logging in the datalogging program as even turning on at all with the sample rate maxed out
2) Not being stored in the ECU in any fashion, including reading for DTC's right after the CEL flashes without powering the car off at all and checking for stored codes after power down and start up via the service connector method, or for me (thanks to eCtune again) the gas pedal/brake pedal method.

And for the record I ignored your first comment because I specifically stated that no codes were stored in the ECU, and I figured you didn't read my post all the way through. That you were just commenting trying to get your post count up so you can access the classified forums, which so many people do. I apologize if that was not the case. If the CEL is not currently on, the only way to read the error is if it was stored, and it wasn't/isn't, like I said.

Yesterday I started the car after changing my oil and wiggled/tugged on any wire I could see to try and get it to stumble, with no luck. I drove in to work today with no CEL coming on at all. I'm going to go drive around the surface streets (lots of 1st gear) on my lunch break and see if I can get it to come on again. Otherwise I have made no changes besides changing my oil, which I don't see why that would be related.
 

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You didn't think of it because the whole concept is wrong.

Go stall your engine by popping the clutch. The CEL should not turn on.

Bottom line: If the CEL turns on, there's a trouble code in the ECU. Figure out how to retrieve it. I suggested one way, but there may be others.
WTF are you smoking. The CEL lights up when you have the engine off and key ON. No it will not STAY lit up but it will light up when you almost stall it or first turn the car to the ON position. Quit spreading misinformation on this site.
 

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The MIL/CEL will come on with no engine power or when it gets close to the point of stalling and that may be why the turn on when bucking.
This^ would only happen if a CEL code is thrown.
WTF are you smoking. The CEL lights up when you have the engine off and key ON. No it will not STAY lit up... Quit spreading misinformation on this site.
This^ is a strong accusation that, in the end, you will retract because if you don't, then you are spreading misinformation.

Read your first quote above. Now compare it to your second quote above. Those are two completely different contexts. What you said in the first quote is wrong. The CEL would only come on in that context if the ECU detects an issue that would throw a CEL code. To demonstrate this point, do the test I suggested the OP do and you will see the CEL does not turn on.

Here are the results from that test posted earlier by the OP, though he later decided to delete the text for some reason:

However, you are correct about the CEL not turning on when the car is stalling from poor driver clutch release. It's the battery light that turns on, not the CEL. Just went outside, set the parking brake, and dumped the clutch. No CEL. Just the battery light.
In your second quote, you are talking about the fact that the CEL turns on for 2 seconds when you turn the key from OFF to ON(II). This system was designed as an easy way to test whether the CEL works. After the engine is started, if you stall the engine or come close to stalling the engine, the CEL should not come on unless a trouble code is thrown.
 

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Discussion Starter #10
I deleted that from my post because I wanted to be sure that it was 100% accurate. I will reiterate though with the car running, parking brake on, dumping the clutch, there was no CEL. Now, I didn't ease the clutch out slowly to the point of stalling (due to the parking brake), I did release it fairly quickly with no additional throttle, and it did stall with no CEL - a quick flash or otherwise.
 

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Hey, man, I don't want to start an argument, but that statement is incorrect.
My statement is correct. You have already done one test that supports it. Please do others, but the answer will not change. It would be abnormal for the CEL to illuminate under those conditions.

eCtune allows me to turn the CEL on for things other than DTC's. So there is the possibility that it can turn on without any trouble code being thrown if there is something causing the ECU to think it is at the rev limiter, or proper RPM for MIL shift light. I'm not saying that this is the case, but that it is a possibility.
Sure, you can modify the CEL, but your CEL is set up to behave as intended by the Honda engineers - turn on when the ECU detects an issue in a sensor circuit.

Also, I have yet to find a way to retrieve it, because it is :
1) Not logging in the datalogging program as even turning on at all with the sample rate maxed out
2) Not being stored in the ECU in any fashion, including reading for DTC's right after the CEL flashes without powering the car off at all and checking for stored codes after power down and start up via the service connector method, or for me (thanks to eCtune again) the gas pedal/brake pedal method.
Have you considered that the ECU or the engine management system is faulty? A remote possibility is an intermittent short in the service connector wire. The latter could possibly (not sure) cause a stumble as it prevents the ECU from adjusting the ignition timing.
 

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Discussion Starter #12
Your statement about the CEL when the car stalls from poor driver clutch engagement has been proven true by me dumping the clutch and getting no CEL.

The following statement you made is not "Bottom line: If the CEL turns on, there's a trouble code in the ECU." The CEL will turn on if there is a trouble code in the ECU OR the tuning program tells it to turn on for some other function. Just because the CEL turns on, that does not mean that there is a trouble code.

Don't get me wrong, I'm with you on this. I think that there is a very slim chance that it is the MIL shift light triggering early because of a faulty sensor reading. It's possible that that's what is causing it, but most likely it is the normal Honda programmed CEL turning on because of a faulty sensor/reading as you said.

Regarding the ECU or EMS being faulty. I have been beginning to question that. I'm not sure what would cause something to go awry suddenly with either, but I know that it has happened to people before, at least with the ECU. With them EMS, I can just delete and reinstall the program and see if that fixes anything. Which I may in fact, do.

But here is what has me more confused now, more variables in the equation. I went out on my lunch and drove the car a bunch. Lots of first gear, some fuel cut decel, some boost, first gear starts, second gear starts, etc. The problem did not manifest at all, no CEL's or anything, except the shift lift.

Things that have changed since yesterday (that I can think of):
1)Changed my oil (same brand and weight and fluid level, just a change)
2)I wiggled wires under the hood while the car was running to try and get it to happen (could have wiggled it back to a good place?)
3)The outside air temp has dropped about 20 degrees. Today is very cold for the time of year

I'm kind of hung up on the oil thing for some reason. I was at the end of my oil interval when this started happening. I know there is the oil pressure switch, which I no longer have, I have an analog gauge. And there is the VTEC pressure switch. But that doesn't get checked until VTEC tries to engage, I think. I'm just wondering if my oil was getting thin and not building enough pressure, it could trigger something? But I don't know what that would be. As far as the outside air temp, I don't see what that would give trouble since there are compensation tables in the tune.
 

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Have you tried disabling the MIL shift light and rev limiter?

I'm not sure what would cause something to go awry suddenly with either, but I know that it has happened to people before, at least with the ECU. With them EMS, I can just delete and reinstall the program and see if that fixes anything. Which I may in fact, do.
ECUs can and do go bad. It's not unprecedented. If you have a chipped ECU, then the chip also could be faulty.

I went out on my lunch and drove the car a bunch. Lots of first gear, some fuel cut decel, some boost, first gear starts, second gear starts, etc. The problem did not manifest at all, no CEL's or anything, except the shift lift.
There's nothing really to do until the CEL comes on and the engine stumbles again. Disabling the extra CEL functions may help to pinpoint the problem.
 

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Discussion Starter #14
Pulled the kick panel and checked the service connector. Everything looked kosher. No accidental paperclip jumpers left behind rattling around. No exposed wires. No visible corrosion or anything out of the ordinary.
 

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Discussion Starter #15
Have you tried disabling the MIL shift light and rev limiter?
This was going to be my first course of action, but now the problem isn't happening. It will be the first thing I do next time it happens...if it happens.

ECUs can and do go bad. It's not unprecedented. If you have a chipped ECU, then the chip also could be faulty.
I have heard of ECU's going bad on people at random times. It is a socketed ECU, running a DEMON emulator. Again, if it comes back, I will pull the ECU and check my solder connections, though I have quite a bit of solder experience so I would be surprised if one failed. That being said, nobody is perfect. I might do this in the meantime.

There's nothing really to do until the CEL comes on and the engine stumbles again. Disabling the extra CEL functions may help to pinpoint the problem.
Agreed. I just have to wait and see what happens. Before it stopped coming on I was trying to make some correlations to no avail. If it only happened first time in first after boost. With the clutch pedal in for a long time, for a short time. Waiting in neutral for a long time or short time, etc. Nothing seemed repeatable.
 

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This was going to be my first course of action, but now the problem isn't happening. It will be the first thing I do next time it happens...if it happens.
If those two additional CEL functions are pure luxury rather than requirements, then consider keeping them both disabled for a while. Then, if the CEL does come on, you are confident that it's trouble code related.
 
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