99 ML430 with some issues.
 

I hate to rehash what's been said on another forum, but I'm not getting much input over there.

This started out with a P0170/P0173 CEL. I changed the MAF, but no luck. Recently, the truck has been sporadically running bad (loss of power, shuddering). Code check revealed the same two codes, accompanied by P0300, P0305, P0306, P0307 and P0308. I found it strange that all these codes were on one side of the engine; however, I replaced the plugs and wires.

I had a tech look at the truck when I had all the codes popping and he recommended plugs, wires and a throttle actuator. He said my MAF appears to be fine.

Since then, I have the P0170 and P0173 codes. I purchased an Actron CP9180 Autoscanner and checked the live data. This is what I got:

These values were taken after the codes had been cleared.

Here's a printout of my values at idle, upon startup:

MIL STATUS OFF
ABSLT TPS % 2.7
ENG SPEED RPM 651
CALC LOAD % 20.3
MAF FLOW g/Sec 5.55
MAP KPA 29
COOLANT �F 208
IAT �F 165
IGN ADVANCE � -13.6
SECOND AIR ATMOS
ST FTRM1 % -1.0
LT FTRM1 % 16.4
ST FTRM2 % -2.2
LT FTRM2 % 17.1
VEH SPEED MPH 0
FUEL SYS 1 CLSD
FUEL SYS 2 CLSD
O2S11 V 0.785
ST FTRM11 % -2.2
O2S12 V 0.780
O2S21 V 0.100
ST FTRM21 % -2.2
O2S22 V 0.065

This is a record of the values after approximately one minute at idle:

MIL STATUS OFF
ABSLT TPS % 2.3
ENG SPEED RPM 659
CALC LOAD % 20.0
MAF FLOW g/Sec 5.41
MAP KPA 29
COOLANT �F 208
IAT �F 167
IGN ADVANCE � -13.6
SECOND AIR ATMOS
ST FTRM1 % 0.7
LT FTRM1 % 16.4
ST FTRM2 % -4.6
LT FTRM2 % 17.1
VEH SPEED MPH 0
FUEL SYS 1 CLSD
FUEL SYS 2 CLSD
O2S11 V 0.155
ST FTRM11 % 0.7
O2S12 V 0.755
O2S21 V 0.210
ST FTRM21 % -1.0
O2S22 V 0.070

I took the truck for a drive (approximately 1/2 hour) and she threw the CEL again, upon startup. Here is a read out of the freeze frame event:

Frame 1 Mod $01
TROUB CODE P0173
ENG SPEED RPM 650
CALC LOAD % 26.6
MAP KPA 36
COOLANT �F 195
ST FTRM1 % -11.8
LT FTRM1 % 16.4
ST FTRM2 % -13.3
LT FTRM2 % 17.1
VEH SPEED MPH 0
FUEL SYS 1 CLSD
FUEL SYS 2 CLS

Can anyone point me in the right direction?

BTW: After resetting the codes, the truck drives fine, sometimes for a day or so, before the P0173/P0170 return. If it was the MAF, wouldn't the problem raise its ugly head almost immediately? Could this symptom be indicative of a fuel pump/regulator/filter problem?

Most likely a bad catalytic converter on the drivers side.

M.B.Doc, I was thinking that too, but wouldn't that cause the O2 sensors to set a code? If the catalytic converter was bad, wouldn't the driveability issues be more apparent? The truck runs very well 99% of the time. Is there a way to test the cat?

Here's a little more info from it throwing codes (P0170/P0173) this afternoon. This, again, was at startup. Prior to the codes being set, I had my wife drive it like a race car. It wasn't until she stopped to pick up lunch that the codes popped:

Frame 1 Mod $01
TROUB CODE P0173
ENG SPEED RPM 550
CALC LOAD % 27.4
MAP KPA 36
COOLANT �F 186
ST FTRM1 % -14.7
LT FTRM1 % 14.0
ST FTRM2 % -16.1
LT FTRM2 % 14.0
VEH SPEED MPH 0
FUEL SYS 1 CLSD
FUEL SYS 2 CLSD

I'm noticing that both times the short term fuel trim has been severely in the negative. Is this indicative of the ECM sensing a rich mixture? If so, that would suggest a blocked cat? Would a cracked/leaking cat show similar symptoms? Any ideas why the codes are popping at startup?

Okay, I just got back from my local import mechanic shop (old friend of mine). He has a new young apprentice, so he was eager to look at the values my scanner recorded.

Based upon what I was told, the long term value should be at 0% and no higher than 3%. The 16% on bank 1 and 17% on bank 2 is way out of specs. Also the -11% and -13% I am seeing on the short term is indicative of the ECM trying to lean out a very rich condition.

He believes there is excess air getting into the system (vacuum line, etc), which is causing this condition. The cat theory he was not sold on. He said that the O2 sensor after the cat would pick that up and pop a code.

He is recommending a "smoke" test to look for the leaks.

I'm still open to suggestions from the forum ... please, don't be shy!

This occurred when she was coming home from work. The truck threw P0305 through P0308 and P0300:



Freeze Frame

Frame 1 Mod $01
TROUB CODE P0300
ENG SPEED RPM 3075
CALC LOAD % 62.7
MAP KPA 99
COOLANT �F 185
ST FTRM1 % 25.0
LT FTRM1 % -4.6
ST FTRM2 % 25.0
LT FTRM2 % -23.1
VEH SPEED MPH 31
FUEL SYS 1 CLSD
FUEL SYS 2 CLSD

It should be noted that I ran the vehicle in the driveway up to 4000 RPM and experienced some missing/slight backfiring. The value of the MAF rose from 5.X g/sec to 27.X g/sec.

Anyone have any idea as to what the heck is going on?