How to test a MAF?

[ak47]

I have a 305 motor from an '86 T/A that is giving me lots of headaches. It just cranks all day long when it's been sitting for more than 4 or 5 hours, and won't start until it warms up. Also, when its running, it is very sluggish at low RPMs. I need to check the MAF, and would also like to check any other trouble codes, but I don't have an ALDL connector, wiring harness doesn't seem to be all there. When I get it running, it will run fine down the highway, but it also seems to run rich, which is why I want to check the MAF. Is there any way to check the MAF directly, like with a volt meter? I tried unplugging it and starting the engine, and it actually didn't seem to change anything. Also, how can I get trouble codes without an ALDL? does anybody know how what wire on the ECM to ground to put it in diagnostics mode, and what wire goes to the check engine light? (I don't have a check engine light, but I'm guessing it gets power from a pin on the ECM?).

Thanks.

[Cashmunson]

do some searches on thirdgen.org for the answers you are looking for

[ak47]

Already did that, I've post on that site too. Everything I've seen describes how to check codes with an ALDL connector and a check engine light, but I don't have either of those. I need to know where the check engine light and ALDL diagnostic wires go back to on the ECM.

thanks.

[duckman]

yes your car does have an ALDL connector. it is located right above the gas pedal on the bottom of the dash. there might be a cover hiding it( this was the case on my 84). If a previous owner has cut the ALDL connector out of your car then your best bet is find another car in decent shape at a salvage yard for the complete wiring harness from under the dash and replace yours. This is a better option than to resplice wires and fry your computer. if there is no check engine light showing look and see if the bulb is blown or just removed. this was a common practice for people who were selling a car with problems and tried to hide them.

[ak47]

Sorry, I should have been more specific, the motor and "complete" wiring harness, and computer, etc. were from an '86 T/A, but I dropped all that in my pickup. I don't see the ALDL connector where it should be according to pictures of a wiring harness from that car, so I'm wondering where the ALDL wires go to so I can still put the ECM in diagnostic mode, and where wire for the check engine light goes, I'm guessing it goes back to the ECM, right? Would you be able to post a picture of the ALDL so I know what it looks like and what color wires come off of it?

Thanks.

[duckman]

disreguard

[duckman]

disreguard last post let me see what i can find in the books

[ak47]

Sounds good, thank you for taking the time to help! I'll check back here later today if possible. In the mean time, I'll try checking some sensors and look for diagrams, etc. as well.

thanks.

[duckman]

ok heres what I found.
the check engine light will be a pink/black wire with a brown/white wire.
the ALDL connector is a 12 pin black plastic connector. not all pins used.
pin A black/white ground
pin B white/black diagnostic terminal
pin C brown A.I.R. (if used)
pin D brown/white service engine soon light
pin E orange serial data
pin F tan/black tcc (auto only)
pin G red/black fuel pump (EFI only)
pin H (not used)
pin J (not used)
pin K (not used)
pin L (not used)
pin M unknown wire color serial data (if used)

ECM connector is as follows.
pin A1 fuel pump relay
pin A2 A/C control relay
pin A3 canister purge solenoid
pin A4 EGR/EFE
pin A5 check engine system check lamp
pin A6 12V ignition fused
pin A7 TCC (auto only)
pin A8 serial data
pin A9 ALDL diagnostic
pin A10 speed sensor
pin A11 mat
pin A12 ground system return

more on next post

[duckman]

pin B1 +12V batt fused
pin B2 fuel pump relay
pin B3 distributor refference low
pin B4 EST HEI spark timing
pin B5 distributor refference high
pin B6 mass flow sensor
pin B7 HEI spark timing retard
pin B8 A/C clutch
pin B9 PSPS
pin B10 park/neutral switch
pin B11 vane air meter mas (analog only)
pin B12 4 cylinder mode

pin C1 EAC
pin C2 air diverter solenoid
pin C3 stepper coil B low
pin C4 stepper coil B high
pin C5 stepper coil A high
pin C6 stepper coil A low
pin C7 TCC solenoid 3rd
pin C8 TCC solenoid
pin C9 fan request
pin C10 coolant temperature
pin C11 MAP
pin C12 not used
pin C13 TPS
pin C14 5V sensor refference
pin C15 injector B drive
pin C16 +12V batt fused

pin D1 ground system return
pin D2 fan
pin D3 6 cylinder mode
pin D4 not used
pin D5 HEI bypass
pin D6 O2 sensor low
pin D7 O2 sensor high
pin D8 EVRV
pin D9 not used
pin D10 ground system return
pin D11 PSPS
pin D12 5V return A
pin D13 5V return B
pin D14 injector B drive
pin D15 injector A drive
pin D16 injector A drive

[ak47]

Perfect!! If I can't find a plug that looks like the ALDL I should be able to use those ECM pin-outs to get the trouble codes, you don't even realize how helpful that was!! :thumbup:

I'll give it a try tonight and post the results back here tomorrow.

Thanks!

[ak47]

Ok, the good news is that I found the diagnostic terminal, and the wires where they go directly to the ECM. The bad news is that when I ground the test pin and hook up a light to the Check Engine wire, I don't get any codes, not even a code 12, the light doesn't come on at all. I tried leaving the light hooked up in normal driving mode and still nothing. I am at a loss as to why I couldn't get any trouble codes, obviously there is something wrong with it if I can't even get a code 12 (yes, the light I hooked up does work). Any ideas what would cause this?

[ak47]

... Also, for some reason my cooling fans come on when in diagnostic mode with the key in run, is that supposed to happen? They are wired up through the factory cooling fan relay.

[duckman]

double check your wiring hookups for everything but it sounds like a bad ECM.
was the vehicle you pulled from wrecked real bad or just so so?

[ak47]

I'm really hoping that's not the problem, I'll check all the wiring again and make sure that's ok. I might try to get it to a shop and let them check the sensors and ECM before I start replacing parts again. I'll keep you updated.

Thanks.

[ak47]

Good news! The starting problem was due to the cold-start injector not getting power. I ran power to the cold-start injector while starting and now it starts like a champ. But then it wouldn't stay running, the idle would just drop off to nothing and it sounded like crap. I unplugged the MAF and tried starting it again, then it ran "great", it held an idle and throttle response was much better. I'm guessing that means the MAF is bad? I am going to replace it in the next couple of days and see if that is the end of my engine troubles.

[ak47]

Final Update: I replaced the MAF and adjusted the idle and TPS, it runs great now! Thanks to all who helped!