Thought I would post this over here too since I'm stumped more than a stump!

Engine in sig ARAP bin modified by me. Drove 70 miles to a friend's house. Ran great. Warmed up the engine the next morning and shut it off to get something from inside.

Came back out, tried to start it... it fired, flared up as usual and died immediatly. Tried 10 more times same thing, throttle seemed to make no difference.

Checked fuel, check spark... getting both.
Unplug the maf sensor... engine runs rough for 2 seconds then the MAF ses light comes on and it idles and drives pretty good minus the being rich.

-Tried two other chips, and burnt another one just to see, no change.
-Tried another ECM (Theory it might be bad), no change.
-Tried two other mafs (disconnecting the battery between each one Wells and Bosch style) No change.
-Went through all the steps to check MAF ses codes 33/34, all checked out good.
-Tested all the grounds in the engine bay, all are good.
-TPS voltage good on scanner and DVOM
-Cleaned IAC, no change.
-Checked for obvious things (Plug wires, connectors, vacuum leaks, burnt wires) nothing.
-Changed distributor completely, no change
-Checked all grounds for resistance, all good.
-Fuel Pressure 41psi, 35 during cranking.


Where do I go from here? Why does it run with the ses light on maf unplugged, but wont run when its plugged in? Something is fubar, and the computer goes to default settings over it when the maf is unplugged.

When the maf is plugged in, I can get it to sort of run by pumping the throttle, sometimes. It tries to pop and studder and sounds kind of like its back firing, or coughing or kicking back.

Help PLEASEEEEEEEE!

 

Either the MAF is bad, the MAF scalar tables are foobar, or there is un-metered air bypassing the MAF.

RBob.

 

In addition to disconnecting the MAF sensor and checking the wires and connector for it. Did you also check the MAF power relay and MAF burn-off relay? They can also contribute to the MAF sensor reading bad. Especially if the burn-off wires are dirty.

 

The other mafs I tried work on my friend's 89 GTA. Mine is a Wells SU145 and we tried his Wells of the same part number, and his factory Bosch unit.

Tried 2 different tunes on 3 different chips and didn't get anywhere. Never touched the maf scalers in them. This setup ran for 500 miles as is now except for the breather (read below)

I did however (unknowingly about how the maf would react) Put a breather in the valve cover instead of the tube that goes to the throttle body. I did plug the throttle body though. It drove fine for 90 miles like that to my friends house. He's a mechanic buy trade and pointed out that there would be air sucked in the breather and gone out through the pcv into the intake... being un metered. plugged the PCV and got nothing, tried the old line back to the valve cover and got nothing.

I will check for intake manifold vacuum leaks. And pull the plenum off to see if a gasket was fubar.

Thanks for the reply Rbob!

Edit: Trickster: I went through the Maf code 33 and 34 diagnostic tests. Which test the relays maf and ecm. All checked out. Guess I could go replace the relays. They are a year old The bosch units have a wire inside the maf (I assume this is the burn off wire you are talking about)... the Wells units do not have that wire.

 

Update: If I let the car warm up with the ses light on...

--Wells maf... I get the flare and die.
--Bosch maf... will idle, rough, maf values bouncing 5-9gm/sec If I put my foot on the throttle a little(.54tps to 1.0tps), the engine doesn't speed up and the maf values don't change... it will only rev up if I romp on it.

According to the scanner my IAC is at 160 steps, and I've got the throttle blades open now almost as far as they will go with the set screw.

Got a burnoff and power relay ordered from the parts store, should be here in an hour. Inspected all the maf wiring I could and found nothing. Also found no obvious vacuum leaks, starter fluid in the valvecover and around the intake revealed nothing.

More ideas?

Edit: Tried the new relays, nothin. Wells maf this time seemed to be about the same as the bosch one.

 

I'd say either wiring or bad ECM. Here's why: with the MAF unplugged once the SES comes on the engine runs OK. In this mode the ECM is ignoring the MAF input and is creating a default gms/sec value from the TPS & RPM inputs.

You have pretty much eliminated that the MAF is bad (by trying known good ones). You haven't changed the scalar tables, and have checked for unmetered air.

That leaves the wiring between the MAF and ECM and the ECM itself. The wiring also includes the connectors.

As it is the car may be driven with the MAF unplugged. GM put the default values in the ECM just for that purpose. IOW: if a sensor dies it won't prevent the car from being driven to a shop or such.

RBob.

 

Rbob, What you say definatly makes sense. I did try my friend's 165 ECM and all combinations of the 3 mafs, and it didn't make any difference either. I started last night working in my 1987 Camaro GM Shop manual to test the ecm leads and such.

Here is what I found so far

Key on Voltage:
-A3 Canister Purge .22v (should be 12)
-A5 SES Control .14v (should be 0)
-B12 Maf Input .05v (should be 2.5)
Engine running is .4-1v and there is a note saying "Varies"
-D4 EST Control .08v (should be 0)
-D12 Burn off Relay control .02v (should be 12)
Looking at wiring diagram with mechanic friend and he thinks that D12 is the computer grounding that wire to activate the relay, even though the book says it should be 12v (thought it is a black wire?).

Key on Ohm Resistance 20k setting
D3- System Ground .07
D10- System ground .07

Looks like my big problems here are the Canister Purge, Maf Input and possibly the burnoff (A3-B12-D12) The others are small, do you think the others are suspect too?

Any more words of wisdom in going deeper or just find out why those are bad?

Thankie! I like having direction. Hurts the head when you don't have any idea at all.

 

It's beyond me now. I found ckt 994 and 900 to be having trouble so I ran a new wire from D12 ECM to Terminal B of the Burn off relay. I ran a new wire from Maf Terminal D to the relays.

Still doesn't work right. Went through more diagnosis, and the shop manual says: Check for open in ckt 998 (Maf Input) If ckt not open Faulty ECM connection or ECM.

Well the ckt is not open. So it must somehow be the ecm.

I tried the resistance on ckt 900 Burnoff (ECM to Burnoff relay) to ground and it had 2.22 resistance on 20k setting. Meaning that its grounding in the ecm for some reason. Which doesn't make sense since I tried a new ecm!

Maf Input 998 (Maf Terminal C to ECM) has 1.24 resistance to ground. So the ecm is grounding it internally also.

Bizzarre.

I'm lost...