Code 55 Lean Condition at WOT

[XfireZ51]

Took the car out after installing the new NGKs. Part throttle is very nice and idle is much smoother. Trying a blast at WOT, I got an SES which was a Code 55. This was a hard code which didn't drop with driving as it had done previously. I went out once again, this time with the scantool. Here's the part of the scan where the Code 55 was set. It happened at the top of the rpm band. I've checked FP and that seems to check out. Also, secondary port throttle is not the cause here.
Any observations are welcome.

http://i187.photobucket.com/albums/x198/Z51Xfire/ZR%20Top%20End/Code55scan.jpg

[-=Jeff=-]

Swap back to your old plugs that you just removed and see fi the Lean condition goes away..

[XfireZ51]

Jeff,

I'm going to take the NGKs and re-gap them to .035-.040, but looking at the scan, something causes the injectors to drop PW. At the same time, the timing goes to 14.1d. My theory is that something happened to cause the injectors to drop PW which then caused the Lean condition with the code 55. This all happened at a point on the rpm range where the Fuel Kill was set, 7175rpm. Just a thought.

[-=Jeff=-]

so set the Fuel kill to 7225.. see if that helps too.. but worst case, go back to the old plugs cause at WOT you had no issues

[XfireZ51]

so set the Fuel kill to 7225.. see if that helps too.. but worst case, go back to the old plugs cause at WOT you had no issues

I have a new cal that I'll load into Ostrich when I get back. I've raised Fuel Kill to 7400rpm. And I'll re-gap plugs to .040".

[Aurora40]

Why does your speed drop from 90mph to 77mph within one frame? It seems weird the line you highlighted as the code setting, because that's when the throttle is closed. Or does that hightlighted line not really signify that?

I can't tell if that one column is R O2 volts, but maybe it is, looks like it goes from .9ish to < .1ish That would certainly seem to indicate a lean condition.

FWIW, I've tapped the limiter several times in my car and it's never set a lean code.

[XfireZ51]

A40,

The Vehicle Speed is in kph. But its still a drop of 8mph or so during an upshift. I was fighting the ASR also. Didn't turn that off which I should have. I wouldn't think Fuel Kill would cause a lean condition but right now looking at all options.

[tpepmeie]

Dom,
pulse widths are in cols. Q & V. Your secondary injectors shut off, it looks like to me.

What does your PT Closed spark advance look like? About 20d at high RPM & Load (14.1+6)? Notice also the pulsewidths have obviously changed after the shift to the PT Closed map, as they never recover to the 23ms range as before the shift.

Todd

[XfireZ51]

Todd,

Exactly. Actually, Closed Throttle SA is set to 16. My suspicion is that the injectors shutdown because of the DRPs. With the injectors shutdown, I got a code 55 which closed the Port Throttle. Question is what happened to the timing there? Car runs fine otherwise. Thanks for your help. Maybe there's something in the logic you could find.

[tpepmeie]

Todd,

Exactly. Actually, Closed Throttle SA is set to 16.

No, what I mean is what is the spark advance in your Port Throttle Closed SA table, above 5000 rpm, 100KPA? I suspect it is around 20d. When the secondaries shut off, the ECM switched to that SA table.

What have you done with the secondary vacuum sensor? If I remember, you have removed the port throttles. Any other mechanical modifications to the port throttle system?

My suspicion is that the injectors shutdown because of the DRPs.

Not following you on this one. What do you mean?


Todd

[Paul Workman]

Dom,

What are columns G and H? Are they LEFT and RIGHT injector current, by chance? If it is current, it raises an interesting question.

Also, would it be possible to remove the label that obscures column "V"? I suspect RIGHT PW is relatively the same as LEFT PW. but I'd like to see that to be sure, as the label covers the PW at a critical point.

p.

[XfireZ51]

Todd,

If you look at the scan, the timing went to 20d even tho the Port Throttle was still open. All of the mechanical bits for the secondary are in there. I removed the throttle plates only. Again, looking at the scan, you'll also see that the secondary MAP signal was more than adequate for maintaining the port throttles open. Its not an issue with the port throttle logic or mechanism. I thought it may have been when I first saw the SES light.
My thought was there may be something wrong with the timing which then caused the ECM to throttle back the injectors

[nowa]

Hi @All :)

column (http://dict.leo.org/ende?lp=ende&p=thMx..&search=column) J Is this your MAP sensor voltage ? If it is I think its too low @wot. It should be 4,88 V, not 4,33 V ( MAP 4,3 V -> ECM less fuel -> code 55 ? ).

norbert

[XfireZ51]

Hi @All :)

column (http://dict.leo.org/ende?lp=ende&p=thMx..&search=column) J Is this your MAP sensor voltage ? If it is I think its too low @wot. It should be 4,88 V, not 4,33 V ( MAP 4,3 V -> ECM less fuel -> code 55 ? ).

norbert




Norbert,

Column J is the TPS voltage. And Column AB is TPS%. MAP is column R.

[nowa]

ok I messed up. You got 4,33 V tps-Voltage before and after the shift. So its not the cause of the problem.

Another theory. Column M shows knock retards ? All over the visible rpm-range ? Whats the strategy of our ECM to prevent/recover from exessive knocks ? (Todd: ECM permanently removes 5d of spark advance when persist knock is detected) Are your new sparkplugs the cause of detonation because they are too hot ?

norbert

[tpepmeie]

(Todd: ECM permanently removes 5d of spark advance when persist knock is detected)
norbert

Norbert, where did you dig that up?:razz: I must have said it in a previous thread. Anyway, that comment was in reference to Low Octane Knock retard, which is not what Dom is experiencing. His is the usual short-term high load knock event. This would not trigger the Low Octane activity.

Dom, the trigger for a Code 55 is a lean O2 reading during power enrichment. This means lean side of the "set-point" in the calibration. My theory is the 55 set, then the secondary injectors shut down (as they are supposed to). That put you into the PT closed VE & spark tables, which is obvious from the pulsewidth change after the code.

because the port throttle plates are gone, the airflow remained high. The O2 readings after the shift are absurdly low, indicating a real lean condition.

Best to get out the FSM and troubleshoot the 55, before tearing into the calibration.

Todd

[XfireZ51]

Todd,

It isn 't my thinking that its something in the calibration. I was only wondering what if anything in the logic might explain the ECM commanding
a lower PW and SA the way it seems to be doing here. I'm not sure if the lower timing is causing the ECM to command a smaller PW or vice versa.
I have looked at the FSM and it basically is pointing to the Fuel System.
We looked at FPressure this weekend and with primary pump fuse out, FP spiked to 48psi and then settled to 42, and the same numbers with both
Primary and Secondary pumps working at key on. I've borrowed an FP gauge with a long hose so as to tape gauge on windshield and will check out pressure with car rolling and at WOT.
My question is if there was a loss in fuel pressure, would that cause the ECM to command a smaller PW? At this point, I would be at a loss to explain how. I'll keep you posted.

[XfireZ51]

Todd,

On Fuel Kill, can you explain RPM/MPH Upper/Lower Error params? Is that the hysteresis? In my bin its set at 2800+rpm.

[tpepmeie]

Not following, Dom. Don't recognize those parameters.

[XfireZ51]

Not following, Dom. Don't recognize those parameters.

You'll find them starting at 614 and going thru 61D. If you could review the hack for the $D0A def, that would help. Here's another question to contemplate. Could it be that the code was written as to ignore the cause of the malf? So even if the ECM was the cause of the lean exhaust,
it would still set a code 55? Or if Fuel Cutoff, then ECM should ignore the Lean Exhaust?
My gut tells me GM would play it safe and not bypass the malf flag even tho it was a previous ECM action that caused the malf in the first place.

[XfireZ51]

Well took the car out again after having re-gap of plugs and raising Fuel Cutoff point. Still set a code at WOT. And I noticed that when I first "got on it', it just didn't feel like it had the grunt. I'm thinking fuel pump.

[-=Jeff=-]

I STILL say.. put the old plugs in and see if the problem is still there.. this way you KNOW for sure if you need a Fuel Pump.. this started AFTER the plug change. why not swap them back, should only take 20min to swap

[tpepmeie]

You'll find them starting at 614 and going thru 61D. If you could review the hack for the $D0A def, that would help. Here's another question to contemplate. Could it be that the code was written as to ignore the cause of the malf? So even if the ECM was the cause of the lean exhaust,
it would still set a code 55? Or if Fuel Cutoff, then ECM should ignore the Lean Exhaust?
My gut tells me GM would play it safe and not bypass the malf flag even tho it was a previous ECM action that caused the malf in the first place.

Dom, I finally checked my disassemblies. Those params are not quite what you have described. You've got Fuel Cut and Fuel Resume RPMs, and Speed limits. There are two separate RPM limits & resume values. One is invoked in "Converter Protection" mode.

Todd

[XfireZ51]

Dom, I finally checked my disassemblies. Those params are not quite what you have described. You've got Fuel Cut and Fuel Resume RPMs, and Speed limits. There are two separate RPM limits & resume values. One is invoked in "Converter Protection" mode.

Todd

Got it. Very much appreciated. I'll be working on fuel system components tomorrow. Least expensive first, Fuel Filter, then onto pumps.

[Tyler Townsley]

I STILL say.. put the old plugs in and see if the problem is still there.. this way you KNOW for sure if you need a Fuel Pump.. this started AFTER the plug change. why not swap them back, should only take 20min to swap

If the plugs are not resistor type they will get noisy and cause rfi problems. This happened several years ago with some of the plugs recommended for the LT 5. I have a set I never installed because of the problems others experienced so take the advice and go back to a set of plugs you know worked.

Tyler

[XfireZ51]

If the plugs are not resistor type they will get noisy and cause rfi problems. This happened several years ago with some of the plugs recommended for the LT 5. I have a set I never installed because of the problems others experienced so take the advice and go back to a set of plugs you know worked.

Tyler

Tyler,

Thanks. I read about that. However, the new plugs I installed are resistor.
The installation of new plugs and the Code 55 are purely coincidental.
Pulled the fuel pumps today and I think I know now what caused the Code55. I'll update with pics once I have car running tomorrow.

[XfireZ51]

On a hunch, I pulled the pumps and what I found wasn't a surprise. I'm guessing there was enough fuel flow for Part Throttle. Once you punched it, it would run until it exhausted the fuel in the lines and then the pump wasn't able to keep up. Now it feels as if it has secondaries even tho they're out. SOTP feels like its really starting to hustle.
Yeah, I replaced the pumps because that kind of restriction could damage them. They looked original equipment.