So my '87 305 TPI Iroc is giving me MAF code 33.. Scanner says "sensor too high"... and my TPS now at idle is .29volts and WOT is 3.29

SO My thinking is... MAF is fine... it's reading said amount of air... but the computer thinks that's wrong, because the TPS reading says the throttle isn't open wide enough to have that much air coming in.

Replace TPS? Sound good?

 

Start with adjust/replace TPS. Sounds good. If fixed my MAF problem a few years ago.......

 

The TPS is possible. It would have to drop below a 1/4 throttle with a couple of volts being read by the ECM from the MAF.

Also want to make sure that the Drk Blue ( terminal D ) wire at the MAF has no voltage for the first couple of seconds when you turn the key on. If it does the burn off relay is suspect to be bad.

The most common failure would be an open in the signal to the ECM via the MAF which is the Dark Grn wire ( terminal C ). any open circut glitches feed to the ECM will also cause it but I would think it would buck sometimes on hard accell...

 

Absolutely! Get that TPS sensor reading correctly. If MAF -vs- TPS readings don't coincide, the ECM automaticly condems the MAF sensor. Once you figure out the TPS problem, you should be OK. Sounds like the sensor is reading OK, just reading low which would require adjustment.

 

So I adjusted the TPS. Had good voltage. Few miles down the road... BANG .29 volts and a MAF SES.

Then I readjust in a parking lot.... good voltage... and maf SES... WTF. wiggle the plug and wiring at TPS a bit... went from .29 to .70 and things inbetween... not 100% sure it's a loose/bad connection... but it's another start.

Go into store come back out.... bad voltage no SES... check while driving home... good voltage no SES.

so much confusion.

 

.29 volts could be part of a reflection being feed to your scanner. Pinpoint test the voltage with a DVOM. Make sure the reading is correct.
The MAF mirrors TPS, however when one fails the other relies on it's readings to feed the PCM. You may be seeing a reflection as the PCM uses the TPS voltage to run the air flow calculations.
You should be pulling a code 22 and your not so Put a voltmeter on it and start with a verification of actual signal voltage out of the center wire of the TPS. Compare to Scan tool.

I am thinking bad maf signal.. Ground circuit or relay..

So....go to the MAF with the engine running and verify it's signals when it has the .29 volts on your scanner for TPS voltage.


MAF test code 33 factory manual 89 model year.

Ignition Off..

Run 12 volts to terminal G of the ALDL connector. This powers the MAF.
With a test light grounded prob terminal E of the MAF. Is the test light on ? If so continue. If not Faulty MAF relay or wiring.

Check terminals A and B with a test light hooked to the POSITIVE
battery cable. Both should light if not you have a bad ground. Then do a voltage drop test. Test A and B to ground with a DVOM. There should be little or no voltage. Voltage on these lines means loose or dirty ground circuit. Voltage on these lines will turn into positive voltage for the MAF. If ok continue.

Ignition On - running

Check terminal D with Voltmeter. It should be 0 volts, if not it's bad burn off relay, ECM or wiring, If 0 volts continue.

Key on Engine off measure voltage at terminal C to terminal A.
at MAF. Should be 4-6 volts if ok suspect bad MAF.

If not disconnect A and B connectors to ECM and repeat
Over 6 volts. Short to voltage in B12 of the ECM to terminal C at MAF.If less than 6 volts Verify ECM grounds and connections if ok replace ECM.

Hope this helps.... Good Luck

 

Make sure you have 5v to the TPS and then check output voltage with a DVOM. If you cant get the TPS to ,54 v and over 4v at WOT replace TPS.......

 

This is what I found out.



MAF test code 33 factory manual 89 model year.

Ignition Off..

Run 12 volts to terminal G of the ALDL connector. This powers the MAF. With a test light grounded prob terminal E of the MAF. Is the test light on ? If so continue. If not Faulty MAF relay or wiring.

(Test light was on)



Check terminals A and B with a test light hooked to the POSITIVE
battery cable. Both should light if not you have a bad ground. Then do a voltage drop test. Test A and B to ground with a DVOM. There should be little or no voltage. Voltage on these lines means loose or dirty ground circuit. Voltage on these lines will turn into positive voltage for the MAF. If ok continue.

(Both lit, and both had no voltage)



Ignition On - running

Check terminal D with Voltmeter. It should be 0 volts, if not it's bad burn off relay, ECM or wiring, If 0 volts continue.

(on the 2000M DVOM setting... I had 14)


Key on Engine off measure voltage at terminal C to terminal A.
at MAF. Should be 4-6 volts if ok suspect bad MAF.

(4.5ish)


If not disconnect A and B connectors to ECM and repeat
Over 6 volts. Short to voltage in B12 of the ECM to terminal C at MAF.If less than 6 volts Verify ECM grounds and connections if ok replace ECM.

(Kind of got confused on this one)



(Wiggled maf connector... and motor died when terminal E was more out than in)
(Wiggled TPS connector... jumped from .54 to .29 volts on the DVOM)

That's what I found... where do I go from here?

 

Ok, Lets start by discounting the TPS voltage problem here. Lets fix the code 33 and then see where it sets afterwards. If you have a TPS causing the problem then the TPS code should be the first code followed by the MAF code.

Ignition on - Voltage reading at terminal D with engine running - Failure is caused by burn off relay circuit sending voltage to MAF .. That's what is setting the code.

Diagnosis as follows....

Disconnect burn off relay .. Repeat test Is voltage present ?

If yes continue - If not go to No Voltage Below..
If voltage present at terminal D with burn off relay disconnected then there is a short to power in the dark blue lead.. Terminal D at MAF to burn of relay.

If no Voltage present : With test lamp hooked to the POSSITIVE battery cable, Probe the Black wire at the burn off relay connecter (terminal F at relay connector ). Does it light now ?.

If no - Replace Relay If yes Continue.. turn ignition off Light should still light with key off ?

If does... Disconect terminal D of ECM and see if test lamp lights at terminal F of relay connector. If it does The wire is shorted to ground from the PCM, terminal D12 to the relay's terminal F..
If it doesn't you need a PCM..

After verification that the 33 is repaired then look at the voltage for the TPS. I bet it's fixed. If it isn't replace the TPS

Good luck and let me know.....

 

I'll tackle this tomorrow, but two quick questions... which relay is the burn off relay... and also.... what is PCM? I know what the ECM is, but the context diverts to a PCM and possible replacement?

 

Next to the booster on the firewall... how about a pic.. woops forgot pic and PCM is the same thing as ECM.. Powertrain Control Modual.

 

the pic....

 

Awesome. I'll let you know how it goes tomorrow.

 

The burnoff relay disconnected.... there is power. So I have a short to power.... in the DRk BLUE wire Terminal D at maf to burnoff relay.

So that means somewhere a wire is touching something it's not supposed to...

Well I unplugged the battery... and started to follow the blue wire from the MAF... and I unplugged the relay connectors.... where each relay has it's blue wire coming out... they connect and go into one... which travels to the maf connector....

well with the battery unplugged... HOW THE HELL... is it that I am reading volted from that 2 wire into 1 point from the relays to the body... Yeah I get voltage... not alot but some. WTF? I'm so confused.

Maybe my DVOM is bad and it really is the burnoff relay? I'm going to go get to new relays and put things back together and see if that does anything

 

Also, when I unplugged the main relay... there was no voltage at D at the maf connector.

 

I screwed up a little here....Sorry I didn't finish reading the block as I was typing it should state..

If voltage present at terminal D with burn off relay disconnected then there is a short to power in the dark blue lead.. Terminal D at MAF to burn of relay. Or .. Bad MAF Main Relay

I do this stuff everyday and something like this can cause you to go around in circles. Hope too much time wasn't wasted..

You have a bad MAF Main Relay ...

I think your measuring voltage from the MAF itself.... DVOM is ok I bet.. The burn off relay just heated the wire inside to a high temp for cleaning. Possible that is what your reading.. You got it now.. I am gonna be gone after about 8:30am Pacific time untill sunday night. If you have a problem.. it could only be something holding the main relay on which I doubt. Untill then I will be checking in for any other updates.. Still intrested in the out come of the TPS voltage after repairs too..

 

Which cable did you disconnect from the battery?

 

I think that in my mad frustration measuring voltage... i had a finger on the metal lead from the DVOM... I replaced both relays... and turned on the car... (it sat long enough to start back in open loop) so I warmed it up until closed loop. Don't have a code... yet. TPS voltage is good... for now...

I'm gonna go drive around for a half hour or so. I'll see what the outcome is.

And I unplugged the NEG battery terminal.

 

Runs good and all. No codes... But the TPS voltage dropped back to .29 again. I'll adjust again tomorrow and monitor somemore.

Replacing both relays though seemed to work!

 

If that TPS won't hold it's voltage setting, just repalce it. The potentiometer in it may be on the way out or something has come loose interanlly.

 

I want to make sure it's in sure need of replacement. Those things are $50 here.

 

Your MAF problem should be solved.. The TPS problem can be checked by verifing that the 5V ref is that .. 5 V and that the ground voltage to the engine block is zero. With low voltage the ground should be ok.. Bad ground normally ='s high voltage.

If all is so then the TPS will be at fault if adjustment is of no prevail.. Glad to see things worked out....