Anyone see what's causing the hesitation? / General Comments

[DramaFoYoMama]

I've been having what I thought was a really bad misfire. I changed the plugs, but that wasn't it. I'm beginning to think it's a fuel delivery problem. Does anyone see anything in this log I took tonight? I didn't scan very many PID's , but there are experts on here that I swear can read an LS1's mind. :) Also, are there any general comments on the scan that anyone sees? I know it runs hot. I'm going to eventually get around to swapping out the thermostat.

BTW, the "misfire" is only below 2k RPM's. As long as I get above that and give it steady throttle, there's no problem. I'm going to swap the fuel filter when it stops raining.

[Delco]

What size cam do you have ?

[DramaFoYoMama]

It's stock. BTW, I've been on this tune for over 2 years with no incident.

6.0 stage III heads, Fast 90/90, 422, FIPK II, speed density open loop

[Delco]

You need to log a wideband and see what is going on , commanded afr looks pretty lean and your o2's never move ?

[DramaFoYoMama]

I don't use my O2's. Also, I keep it lean under cruise, but you can see that it goes to 14.68 (sometimes a little lower) under acceleration.

[5.7ute]

Just cause you are commanding a certain AFR doesnt mean you are getting it. Best to follow Delco's advice & do a log with a wideband.
I am pretty sure that trying to log misfires without a working maf is pointless as they dont work without it.

[DramaFoYoMama]

I originally tuned it with an LC-1, but I'll get it hooked up again when I get some time. Thanks for noting that the misfire reporting doesn't work without a MAF. I never knew that.

[joecar]

In you previous logs, what was your idle MAP kPa...?

[joecar]

You might be too lean for throttle tip-in... as 5.7ute said a wideband is needed to verify this.

[DramaFoYoMama]

I'm not sure what my idle MAP pressure was before. I'd have to dig out my old laptop hard drive. As for the tip-in, it was never a problem until about a month ago. I'm going to have to break out the wideband, but I'm not going to be able to do that until May. I have a ton of work I have to get done in the next month.

[joecar]

You may have developed an air leak, or your MAP sensor may be failing (you'll need to check these)... or something else.

You would stiil need to check with a wideband as Delco said.

What car is it...?

[jfpilla]

You may have developed an air leak, or your MAP sensor may be failing (you'll need to check these)... or something else.

You would stiil need to check with a wideband as Delco said.

What car is it...?

Joe,
It's a 2002 Camaro.
Do the 02 sensors keep recording in OL in these cars? They do in mine. He has one sensor that looks like it's dying, if it should be recording.
It's not recording any misfires. The TPS drops to 0 when the timing goes away?
Joe

[joecar]

Joe,
It's a 2002 Camaro.
Do the 02 sensors keep recording in OL in these cars? They do in mine. He has one sensor that looks like it's dying, if it should be recording.
It's not recording any misfires. The TPS drops to 0 when the timing goes away?
JoeG'day Joe :grin:


Yeah, I've been thinking about his log...

The O2 sensors should keep logging in OL...
I see what you're saying about S11, it may already be dead (hovers around 500-600mV without switching when AFR is near stoich).

S21 shows switching near stoich, but the rest of the time it is indicating very lean, which may be due to airmass being wrong;

If the airmass is wrong, that would explain the spark advance being wrong at closed throttle (it's going negative, I would have expected 40 degrees or so)... :shock: ...his spark advance graph does look very strange...

At closed throttle his MAP is 49kPa... and he has the stock cam... I compared this to my stock cam/heads 2001 Firebird and I get 32 kPa at idle and 20kPa at closed throttle coasting (steady vehicle speed)... He has heads, but I wouldn't imagine they would cause as much difference to idle/coast MAP values as a cam would, would they...?

If the airmass is wrong, there may be airleak(s) or the MAP sensor may be bad...
he should check for both of these.

I'm wondering if something is wrong with TPS... it never goes very high, yet he accelerated to 70 MPH or so...
He should check the TPS also.

He does ask if it would be a fuel delivery problem...
He should change the filter, measure rail pressure, and possibly measure flow (as specified in the service manual... heed the gaoline warnings).

He said speed density... when MAF is failed, misfire detection is disabled, so the misfire counts will stay zero.

If it's as lean as S21 is indicating, then that could cause misfires at low speeds.

What causes misfires: not enough fuel and/or poor quality spark (among other things)...
He should probably check the plug wires also, and test spark "strength" using a spark tester
(looks like a spark plug with no ground electrode and a grounding clip).

Cheers,
Joe :grin:

[joecar]

I edited my post.

[jfpilla]

Joe,
Nice writeup. Hope he follows your ideas.
"He said speed density... when MAF is failed, misfire detection is disabled, so the misfire counts will stay zero."
In all my years of tuning I did not know that. I read it the other day, but forget. A conditon befitting my age.:help2:
Joe

[joecar]

Joe
Thanks.
lol... I forget stuff all the time... I write stuff down in a notebook, and then I forget where I put my notebook... :hihi:
Cheers
Joe
:cheers:

[DramaFoYoMama]

Just popping in to answer some questions/remarks about my tune. The reason it has negative spark advance at idle is because I designed it that way. It pulls a shit ton of vacuum at idle, and i wanted the RPM's to be lower. Therefore, I pulled a lot of timing out of it. I can redline it, and the RPM's will drop back to where I want them consistently without any hunting. It took me a while to get it dialed in. As for the TPS, there's nothing wrong with it. It's a stroker motor on a 28" tire. I didn't think it was necessary to mash the gas. :doh2: I'll get my old laptop drive out and post some old logs. As far as I can recall, the MAP didn't seem off to me. I changed the fuel filter this morning, but I didn't drive it today. I'll report back tomorrow.

[DramaFoYoMama]

BTW, I'm below sea level in Houston, TX. That might explain the difference in MAP readings between yours and mine.

[DramaFoYoMama]

I also forgot to add that the reason I stopped using the O2's ages ago is because my exhaust is dumped about 18 inches after the collectors. They were constantly getting mucked up and unreliable. They have always read lean, even when brand new. I'll also post some logs when I get the wideband rehooked up, just so you guys don't think I'm crazy. :)

[joecar]

DFYM,

Do this test: key on engine off, what does the scantool show for MAP kPa...?
If you're below sea level, then you should see a solid 101 kPa.

I assume that you tested MAP with a vac gauge while reading the scantool, and that you tested TPS while reading the scantool (I'm just trying to make sure ;) ).

I would have expected a stroker to pull better vacuum with the stock cam regardless of heads... if your MAP sensor is good, then you could possibly have an air leak...

Air leaks don't seem to matter too much as the RPM increases, but at lower RPM they do influence manifold pressure.

Check your fuel rail pressure.

Also, do this:
- get a spark tester (the spark plug looking thingy) from AutoZone, and test coil for spark strength... the tester has no ground electrode, so if the spark cannot jump from the center electrode to the edge then that coil and/or wire is bad;
- ohm your plug wires while wiggling them around; they should all read consistent, and all 8 readings should be close;
- run engine in the dark (I mean pitch black dark) and see if your plug wires are glowing or arcing... if they do, replace them;

Misfires are one of the most difficult things to diagnose... :doh2:

Cheers,
Joe
:cheers:

[jfpilla]

I wonder if dropping that much timing is causing it to load up with fuel? How did the plugs look?

[joecar]

Good point.

[DramaFoYoMama]

I'm not at home right now, but I have them sitting in the garage and can take pics if you want. They were all white, which means they were run lean, correct?

Joe, I'll do those tests as soon as I get some time.

[joecar]

Take your time, no worries.

[DramaFoYoMama]

It was the fuel filter. It runs a lot better now!

[Ritch]

and it seemed to be good under load at higher RPM?

just looking to clarify as I am learning the suttle art of diagnosis aswell

[DramaFoYoMama]

No, it was also breaking up under load at higher RPM's. However, it was fine under higher RPM's as long as there was no throttle transient response (aka steady throttle). I really didn't think the filter was the problem, but it was. I was just going to keep throwing money at it until the problem went away, so I'm glad it's over. :grin: