Ok, here's the deal...

Friday night I took my ECM out to replace my Hypertech chip with the factory one. Car ran fine. Saturday night, I changed the coil and the upper radiator hose, and when I did, the car ran like crap afterwards. Questions:

1) If I had done damage to the ECM when changing the chip, wouldn't it have shown up right away? The car ran great until I did the coil and hose.

2) Is it possible I whacked the MAF sensor by accident when changing the hose, and fried it? Reno brought this up as a possibility, and it does make sense. I know it has NOTHING to do with the coil though....

HELP!!

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Jason E
The former third gen...
'89 Camaro RS 2.8

The future third gen...
'87-'92 IROC, GTA or Z28

The driver...
'95 Grand Am SE 3.1 Coupe
Alpine swing face 60x4 CD player

Long Live #3...

 

i did that, went to autozone and got an MAF for 40 bucks and no problems with it since. have u tried the unplugging test?

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" I'd rather run last in a full out race, than to NOT run at all ".

[This message has been edited by Graeme'sFirebird (edited March 05, 2001).]

 

Unplugging the battery?? Yes. The ECM?? Uh uh...I can do that though

40 bucks eh??? Interesting....other thoughts???

 

uhm.. the 'unplugging the MAF' test... or the giving it a 'firm but light' knock a few times and seeing if the car stumbles

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'86 Camaro SC, black /w silver racing stripes
2.8l MPFI/700r4 /w special 2nd gear delete option
In search of new v8 engine & transmission, now contemplating t5 swap to get me out of this mess.
MSD coil, Accel 8mm wires, SplitFire plugs, Gabriel hijackers

 

btt....c'mon Tom, enlighten me

 

I swapped airbox tops with my friend's camaro, and his MAF still gave me the same code. Where should I look next?

 

Hey Jason, didn't see this msg, it got buried with all the BS being spouted here lately by people that have nothing useful to contribute here.

I think your ECM's probably fine. If you fried it, yeah, your car would've thrown a code (or, more likely, have ran very crappy- if at all!) pretty quickly.

Since you've got the code 34 from the computer, you don't need to do any of the "tap the MAF and check the idle" or "unplug the MAF and drive to see if the car doesn't stall anymore" tests. Those are usually done if the car's acting funny but doesn't throw a code.

Good call on trying your friend's sensor! Since that one threw the code also, then it sounds like a wiring problem. I had a bad 3-pin MAF connector that would work fine if I pushed on it, but throw a code if I let go. I wound up replacing the whole MAF harness (connector, relay, fuse holder) with a junkyard one for $5 instead of bothering with replacing just the connector.

The MAF harness only goes "up" to the main engine harness with three wires! One wire is a black one, which goes to a common ground point- about 8 other ECM black & black/white wires tie into it. That point is located near the main harness, by the blower motor, and is covered with tape inside the wire loom. One wire is black & pink, which eventually goes to your ignition switch to "activate" the MAF system. The last wire is the orange/black MAF signal wire, and it runs inside the same harness. All the rest is self-contained... the only wires you splice are the two I just mentioned. The rest of the wires "bolt in" near the MAF. I made my splices using a soldering gun, solder, & heat-shring tubing.

Okay, so, that taken care of, remember my code 34 chart? All you need is a voltmeter (digital or analog, doesn't matter) and a warm day (which I'm sure we're not going to have lately, so make that a "warm garage"). All the wires at the MAF end get tested here, and if all the wires test okay, what next?

Well, could be a bad connector. That's a hard one to diagnose, I was able to wiggle mine and it would go from "no SES light" to "SES light on" to "stall". You can look for corrosion on the terminals of the connector, too.

The last possibility... a fried ECM, but I don't think that's the case! Anyway, here's that code 34 chart again! Good luck... let us know what you find. Hopefully it's just a blown MAF or GAGE fuse.


........................................................................
-----------------------------------------------
DIAGNOSTIC CHART FOR CODE 34 (2.8L MPFI ENGINE)
---------------------------typed by Tom P------

First off, they want you to check out the air intake duct for being loose or
damaged.

Since you are getting the code 34, and no other error codes, we can kind of jump into
the middle of the chart:

1. Ignition off. Disconnect the MAF sensor wire. Connect a voltmeter between the
____harness pin "B" (center) and ground.
_______Less than 1 volt? Go down to "1A"
_______Over 4 volts? Go down to "2"

____1A: Disconnect ECM A-B connector. Check circuit 528 (brown/white, on connector
_________"B", terminal #6) for an open or short to ground. If it's not open/shorted,
_________it's faulty ECM connector terminal B6 or a bad ECM. By the way, this is the
_________MAF's "signal" wire.

2. Connect a test light between MAF harness pins "A" & "C".
_______Light on? Go down to "2A"
_______Light off? Go down to "3"

___2A: Faulty MAF sensor connection or sensor. So since you've tried two sensors,
________I'd imagine the connector's at fault. Try checking for corrosion on the
________connector's pins- I had that happen once. Also, try wiggling the connector,
________and seeing if you get a SES light. If I wiggle my current one, I can make
________a code 34 set, and the car almost stalls. I've gotta get another connector
________from a junkyard... Pep Boys sells new ones, but for an outrageous price.
---------update 10/2000: I replaced the connector (actually, the whole MAF harness!)
---------with one from a junkyard car. No more connector problems!

3. Connect a test light between MAF harness pin "A" and ground.
_______Light off? Go down to "4"
_______Light on? Go down to "3A"

___3A: The ground wire for your MAF, which is MAF harness pin "C", is open. Fix
________the problem with the black ground wire, either it's bad or burnt thru or
________it broke at the passenger-side-upper-frame-rail grounding point (a ring
________terminal on a screw).

4. Disconnect MAF relay, ignition "on" (not "start"). Connect a test light (at the
____relay connector) between CKT 840 (brown) and ground, and CKT 39 (black/pink) and
____ground.

____Okay, now, the MAF relay is located between your air filter box & radiator, on the
____radiator support, I believe. It should have one long black connector to the harness,
____NOT two connectors (one black and one gray)- that ones for your flip up headlights.

____The test on CKT 840 checks to see if voltage is getting from your MAF fuse to the
____MAF relay.

____As for CKT 39, that's controlled by your GAGE fuse. (So that's what it does! Cool.)
____It comes on with the car's ignition- that's why you need the ignition "on". When this
____black/pink wire gets power, it flips the MAF relay's magnet ON, which basically switches
____the MAF on- that's how power gets from CKT 840 to the MAF.

_______Only one light? "repair the open circuit".
__________No light on CKT 840? See "4A"
__________No light on CKT 39? See "4B"
_______Both circuits are fine? Go see "5"

___4A: If no light on CKT 840, find the MAF fuse- it's under your hood, screwed down
________to the upper-frame-rail on the passenger side of the car, closest to the
________headlights. You'll see two little black boxes, each with two wires coming out
________of them, screwed down to the upper frame rail by one screw each. One of them
________has a red wire and a BROWN wire coming out of it- that's your MAF fuse holder.
________Pop the top off to see the MAF fuse. (The holder with red & orange wires is for
________your computer and fuel pump.)

________If the fuse looks fine, try replacing it anyway... I've had that happen to me-
________the fuse looks fine but's really shot. Perform test #4 again. Still no light?
________Probe the MAF fuse holder's RED wire with a test light to ground. This checks
________the MAF fuse holder's connection to the positive-junction-block, located on the
________passenger side of your radiator support. If it's bad, follow the red wire to
________the junction block & fix it. Do test #4 again- still no light? Check
________for corrosion on the MAF fuse holder's contacts. You should get a light by now-
________unless your test light's shot!

___4B: If no light on CKT 39, check the GAGE fuse in the fusebox. As I said up in "3A",
________if the fuse looks fine, try replacing it anyway. Do test #4 again. If you've
________got no light, you get to trace CKT 39 thru the firewall, so hopefully you get
________a light on this one. This one would be a bitch to fix. All I could tell ya is
________that the black/pink wire goes to the GAGE fuse, and the GAGE fuse gets turned
________on when your ignition switch gets turned to "on".

5: Connect a test light between circuit 840 and CKT 450 (black ground wire from the
____relay connector).
_______Light off? See "5A"
_______Light on? See "6"

___5A: Fix the bad ground wire (open on CKT 450) from the relay to the chassis.
---------update 10/2000: This is buried! It follows the wiring harness along the
---------passenger side lower frame rail. You'll have to trace it the whole way. It
---------joins with 5 or 6 other ground wires at one point. Then, after that junction,
---------one wire goes to a ring terminal on the rear driver's side head.

6. Check out the condition of the orange/black wire that goes from pin "A" of the MAF
____connector to terminal "E" of the relay. If this wire is fine (not shorted or open),
____then your relay's bad... you could get a junkyard one but I think a new one is only
____$10 or so from GM.



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-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
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