PCM to MAF issues. Not a "Pink" wire issue.
11-09-2008, 07:05 PM
#1
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Join Date: Jun 2008
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PCM to MAF issues. Not a "Pink" wire issue.
Hey guys,
The car is a '94 A4 Z28 Camaro. It has a Cast Iron Headed Lt1 in it with full bolt-ons, CC306 on 114 LSA, 1.6 GMPP RR, 26918 Beehives, '95 PCM w/ CC306 M6 tune from Ion and T-56 swap from a '95.
Right now, the only code it is throwing is Code 48 MAF System Failure. However, it is pulling 7-8* of knock constantly and thousands of counts due to open exhaust through the Y-pipe. (It's getting a full cat-back as soon as the MAF issue is resolved.)
When we tested the car, we tested for +5V on pin B19 at the PCM connector, mid-length in the wire itself (The yellow wire running to the MAF Sensor) and at the MAF sensor connector. At all of those places we read a constant .25x mV throughout our testing, with a brand new multi-meter.
So far we've (in this order) replaced the MAF Sensor pigtail on the engine harness, tested, switched pcm's with the original '94 PCM with a stock tune for A4, tested, swapped MAF with a '95, tested, pulled entire engine harness and redid all the splice connections and replaced any cracked, burnt, discolored, ect. wires, and made sure we soldered everything and used heatsink wrapping. Brand-new heat wrapping was used for the final touches, also. After putting back in the wiring harness and testing on both sets of PCM's and MAF sensor, we still got all the same readings. (.25X mV) instead of a constant +5V.
Also, we know we have a good grounds at the MAF connector, and everything else for the PCM. And on the pink wire, we always see a constant 12.xx V, so we know those parts of the system are good.
Is there anything you can think of that we might of skipped or not thought of? We know we should be getting +5V right at pin B19 on both of the PCM's but we're not. Is there a possibility that both PCM's are fried on thier MAF circuts? We're at a loss here. Any suggestions?
The car is a '94 A4 Z28 Camaro. It has a Cast Iron Headed Lt1 in it with full bolt-ons, CC306 on 114 LSA, 1.6 GMPP RR, 26918 Beehives, '95 PCM w/ CC306 M6 tune from Ion and T-56 swap from a '95.
Right now, the only code it is throwing is Code 48 MAF System Failure. However, it is pulling 7-8* of knock constantly and thousands of counts due to open exhaust through the Y-pipe. (It's getting a full cat-back as soon as the MAF issue is resolved.)
When we tested the car, we tested for +5V on pin B19 at the PCM connector, mid-length in the wire itself (The yellow wire running to the MAF Sensor) and at the MAF sensor connector. At all of those places we read a constant .25x mV throughout our testing, with a brand new multi-meter.
So far we've (in this order) replaced the MAF Sensor pigtail on the engine harness, tested, switched pcm's with the original '94 PCM with a stock tune for A4, tested, swapped MAF with a '95, tested, pulled entire engine harness and redid all the splice connections and replaced any cracked, burnt, discolored, ect. wires, and made sure we soldered everything and used heatsink wrapping. Brand-new heat wrapping was used for the final touches, also. After putting back in the wiring harness and testing on both sets of PCM's and MAF sensor, we still got all the same readings. (.25X mV) instead of a constant +5V.
Also, we know we have a good grounds at the MAF connector, and everything else for the PCM. And on the pink wire, we always see a constant 12.xx V, so we know those parts of the system are good.
Is there anything you can think of that we might of skipped or not thought of? We know we should be getting +5V right at pin B19 on both of the PCM's but we're not. Is there a possibility that both PCM's are fried on thier MAF circuts? We're at a loss here. Any suggestions?
11-10-2008, 05:25 AM
#2
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Location: Hell was full so they sent me to NJ
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When you tested the voltage at the PCM pin, did you have the harness disconnected from the PCM? If it still showed only .25mV (you actually are getting 1/4 of a millivolt?) you have a PCM problem.
Knock counts in the "thousands" do not mean anything by themself. Its how fast the knock counts are changing. "Counts" is a field that continually increases when the PCM detects engine operating conditions that might cause knock, particularly after the PCM sees a high level of activity on the knock sensor. After the count reaches about 64,000 the field resets to "0" and starts increasing again. It isn't unusual for the knock count to increase by a few thousand at startup.
The continuous knock retard is often the result of a failed knock sensor or sensor circuit. Are you using the correct 4,000ohm 93-95 knock sensor, or do you possibly have the 96/97 100,000ohm sensor, which will set a code and cause knock retard?
Knock counts in the "thousands" do not mean anything by themself. Its how fast the knock counts are changing. "Counts" is a field that continually increases when the PCM detects engine operating conditions that might cause knock, particularly after the PCM sees a high level of activity on the knock sensor. After the count reaches about 64,000 the field resets to "0" and starts increasing again. It isn't unusual for the knock count to increase by a few thousand at startup.
The continuous knock retard is often the result of a failed knock sensor or sensor circuit. Are you using the correct 4,000ohm 93-95 knock sensor, or do you possibly have the 96/97 100,000ohm sensor, which will set a code and cause knock retard?
11-10-2008, 03:41 PM
#3
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We've tested Pin B19 with the connector plugged into the computer and the ign on but engine not running. We always get a constast .25x mV. With the pcm unplugged, we have hooked up a 6v test to make sure the wire itself is actually conducting electricity. Everytime the wire itself tests out fine with our multimeter. Is there any chance that we have a different issue going on here causing the pcm to not send the +5V to the MAF Sensor? Today we bought another PCM from a junkyard and are still getting the same exact results.
11-11-2008, 05:21 AM
#4
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Location: Hell was full so they sent me to NJ
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Maybe I missed it.... but have you measured the voltage on the PCM pin (NOT the harness pin) with the harness NOT connected? I suggested that many posts ago, but I've never seen an indication that you measured it that way. .25mV is essentially "0" volts. What does your meter read when you connect it across a short length of wire?
11-11-2008, 01:32 PM
#5
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Yes we have. It tested the same .25x mV without the black connector plugged into the PCM. Actually by now, we've done that with all 3 PCM's we have. Sorry, for not clarifying that much. We've actully tested the computer pin, wiring harness pin, wire within the harness, MAF connector, and the MAF itself. We have 3 PCM's and 2 MAF's now, all have been tested with the exact same reading. At this point in time, we're confident that it has NOTHING to do with the actual circut itself and we have some other issue causing the problem.
And just so everyone knows, this is only ONE issue that we've been trying to focus on and fix here recently. The car was bought about 5 years ago with 120K on the Odometer. My room-mate installed a K/n and Injectors. No tune, nothing. The car always ran rich and I could never convince him that he needed a tune for those injectors. Nothing major happens with the car for awhile just couple different exhaust set-ups and tranny went out twice. 2 years ago, the original Lt1 got replaced with an iron-headed Lt1 and shortly after that the Auto went out, the car sat. Well during this time, I was gone for the Marines so my buddy decided he wanted a 6-speed swap. I gave him EVERYTHING for the swap, even let him use my car (I had a '95 t-56 Camaro w/ 56,xxx on the odometer) for basically a parts car. I didn't care, it needed paint and an engine anyways. Well instead of pulling the pins out of their connectors, he cut everything and tried splicing in the VSS, skip shift, ect. Well basically all he managed to get working out of that was to get the car movable. At the same time, a CC306 went into it kinda half-a$$ed but running. So then the car sat for a year or so with overheating problems, tranny issues, wouldn't really run right and never moved.
When I got back home in April, we started working on it somewhat here and there and it hasn't been until recently that we exploded into this "Gotta fix the Camaro" attitude. Actually kinda spent over 3k in the last month, just to get parts that my buddy skipped over, broke, or for whatever reason didn't have on the car.
Here's the list of what we've gotten fixed/working properly in the last 4 weeks.
Vss
7* +.050 locks for the 26918 beehives (He installed the beehive springs with stock locks and actually ended up breaking one before he would listen to me.)
New Beehive 26918 spring
New plugs and 02 sensors
Pacesetter Long-tubes (YES, the car had a cam but no headers before I got home... WTF!!!)
Systems that I know still are messed up/need attention:
ABS Inop is on, dunno why yet. Actually haven't looked at it yet. This MAF is pissing me off too much.
Skip shift isn't connected at all but is deleted out of the computer.
Reverse lights don't work.
Reverse lock-out selenoid is busted off the tranny housing. Originally I broke a piece off the tranny where the torsion bar mount screws into the side of the tranny, on my car it was fine because I had the torsion bar welded to that mount, he used his torsion bar and tried driving the car with it not connected and broke the reverse selenoid off the rear section of the housing (actually looking for one if anyone has an extra!))
no rear exhaust past the new y-pipe, we waiting for this MAF issue to get solved before we dump too much more money into it.
The starter has a push-button start on it too. He doesn't think VATS went out (disabled now) but it started having problems and because it was "cool", he put in a push button start. WOW....
Any suggestions?
And just so everyone knows, this is only ONE issue that we've been trying to focus on and fix here recently. The car was bought about 5 years ago with 120K on the Odometer. My room-mate installed a K/n and Injectors. No tune, nothing. The car always ran rich and I could never convince him that he needed a tune for those injectors. Nothing major happens with the car for awhile just couple different exhaust set-ups and tranny went out twice. 2 years ago, the original Lt1 got replaced with an iron-headed Lt1 and shortly after that the Auto went out, the car sat. Well during this time, I was gone for the Marines so my buddy decided he wanted a 6-speed swap. I gave him EVERYTHING for the swap, even let him use my car (I had a '95 t-56 Camaro w/ 56,xxx on the odometer) for basically a parts car. I didn't care, it needed paint and an engine anyways. Well instead of pulling the pins out of their connectors, he cut everything and tried splicing in the VSS, skip shift, ect. Well basically all he managed to get working out of that was to get the car movable. At the same time, a CC306 went into it kinda half-a$$ed but running. So then the car sat for a year or so with overheating problems, tranny issues, wouldn't really run right and never moved.
When I got back home in April, we started working on it somewhat here and there and it hasn't been until recently that we exploded into this "Gotta fix the Camaro" attitude. Actually kinda spent over 3k in the last month, just to get parts that my buddy skipped over, broke, or for whatever reason didn't have on the car.
Here's the list of what we've gotten fixed/working properly in the last 4 weeks.
Vss
7* +.050 locks for the 26918 beehives (He installed the beehive springs with stock locks and actually ended up breaking one before he would listen to me.)
New Beehive 26918 spring
New plugs and 02 sensors
Pacesetter Long-tubes (YES, the car had a cam but no headers before I got home... WTF!!!)
Systems that I know still are messed up/need attention:
ABS Inop is on, dunno why yet. Actually haven't looked at it yet. This MAF is pissing me off too much.
Skip shift isn't connected at all but is deleted out of the computer.
Reverse lights don't work.
Reverse lock-out selenoid is busted off the tranny housing. Originally I broke a piece off the tranny where the torsion bar mount screws into the side of the tranny, on my car it was fine because I had the torsion bar welded to that mount, he used his torsion bar and tried driving the car with it not connected and broke the reverse selenoid off the rear section of the housing (actually looking for one if anyone has an extra!))
no rear exhaust past the new y-pipe, we waiting for this MAF issue to get solved before we dump too much more money into it.
The starter has a push-button start on it too. He doesn't think VATS went out (disabled now) but it started having problems and because it was "cool", he put in a push button start. WOW....
Any suggestions?
Last edited by FBodyBros; 11-11-2008 at 01:35 PM.
11-11-2008, 05:51 PM
#7
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Join Date: Jun 2008
Posts: 102
We have two... The original '94 and an automatic harness out of '95 for connectors. We've pulled it out and completly rewired everything that my buddy had ****ed up with the actual wiring. Honestly, we've been tempted to go ahead and only buy a PERFECT T-56 '94 Harness and be done with it, but we should have everythiing to fix it already...
Not to mention. What if that doesn't solve the problem? Hate to say it but that's been happening a lot with this issue. 3 Pcm's.. 2 MAF Sensors's... and 2 Wiring Harnesses....
Not to mention. What if that doesn't solve the problem? Hate to say it but that's been happening a lot with this issue. 3 Pcm's.. 2 MAF Sensors's... and 2 Wiring Harnesses....
11-21-2008, 04:44 AM
#10
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Join Date: Feb 2000
Location: Seattle, WA
Posts: 1,445
Systems that I know still are messed up/need attention:
ABS Inop is on, dunno why yet ... Reverse lights don't work.
ABS Inop is on, dunno why yet ... Reverse lights don't work.
Reverse lock-out selenoid is busted off the tranny housing. Originally I broke a piece off the tranny where the torsion bar mount screws into the side of the tranny, on my car it was fine because I had the torsion bar welded to that mount, he used his torsion bar and tried driving the car with it not connected and broke the reverse selenoid off the rear section of the housing (actually looking for one if anyone has an extra!))
Best solution is to toss the whole "mount to tranny tailshaft housing" idea and get an aftermarket tranny brace. It'll replace the normal brace that goes under the tranny mount and provides a new metal bracket for the torque arm to fit into. No need to modify or move the torque arm as the bushing is reused and stays in the same place... but now the torque arm wll push up on the crossbrace/floor of the car, instead of pushing the tailshaft away from the tranny mount.
11-21-2008, 11:31 PM
#11
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Join Date: Jun 2008
Posts: 102
Thanks for the info. After we turned off the MAF and started running speed density, we've come to the conclusion that even if we did fix this MAF problem the car currently has, there's still too many minor issues that we want to get worked out like front oil pan leak, reverse lights, LCA brackets and subframe connectors to install, find a new tailhousing for our T-56 and reverse lockout selenoid, not to mention fix minor interior pieces then paint. So obvisously it's gonna be awhile. Getting into this project, we planned on initial test drives in the spring. After we got the car fun to drive around again, we realized there's still little things that need attention. Honestly, this car is a huge money pit but it's the only F-Body that any of my friends actually still have over the years so we all are donating parts and time to get it where it should be.
Did you see my post in advanced tech? https://www.camaroz28.com/forums/sho...d.php?t=650111
That's another issue with this car. Honestly, I'm almost ready to buy a new engine harness and a/c system to put back on the car. Too bad Christmas is right around the corner...
Did you see my post in advanced tech? https://www.camaroz28.com/forums/sho...d.php?t=650111
That's another issue with this car. Honestly, I'm almost ready to buy a new engine harness and a/c system to put back on the car. Too bad Christmas is right around the corner...
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