Re-manufactured Maf Bad? Code 34

cski68 · Sep 29, 2019

Hello from Sweden,
My 88 Callaway twin turbo is completely restored but for one little problem, a code 34.
My original MAF got water inside the housing and never worked after that. (code 33 even with it plugged in) I purchased a reman MAF and installed it with an almost immediate code 34. I then went out and bought new power and burn off relays, no change. I should mention that I have a new IAC and adjusted it and the TPS to the shop manual Idle specifications. I then bought a used MAF in working condition from an 87 trans am which threw the same code 34.
I have tested the signal at the MAF connector from the ECM at 5v ignition on MAF unplugged and 2.4v plugged in ignition on engine stopped. When I start the engine I get .17v to near .3v on the (green) signal wire at idle with my digital meter. I get 12v on the purple wire, ignition on engine off and near 14v engine on. Grounds have been checked at the MAF connector and are good.
I am nearing my wits end and I'm considering getting an MAF from Blower works. It is much better than original OEM but requires some modification to the ECM harness and new Eprom not to mention $300-500 depending on accessories.
I guess I am just looking for any possible problems I may have overlooked before I spend the cash on a new MAF so any advice would be greatly appreciated.

I don't know if there are any European subscribers to this forum but if so, below is a video of my 1988 Callaway twin turbo Corvette #34 which will be for sale after this problem is sorted out. The video was taken before my MAF got wet.

Grumpy · Sep 29, 2019

Trouble Codes › GM OBD Trouble Codes › GM Code 34
CODE 34 - MAP Sensor or MAF Sensor depending on the engine
Trouble Code 34 indicates that the Mass Air Flow (MAF) sensor is reporting less air is entering the engine than makes sense based on RPM and TPS. The MAF sensor produces a frequency output; around 30 Hz at idle to 150 Hz under acceleration. The frequency varies proportionally to airflow. The ECM monitors the frequency and thus determines airflow into the engine. Typical idle MAF is 5 to 7 grams per second.
look for vacuum leaks and leaking gaskets and test sensors
chances are excellent your issue is related to a defective sensor or loose electrical connector or leaking vacuum hose,
Id also check oxygen sensors and catalytic converters, and replace the two relays (MAF & burn off) on the engine compartment fire wall near the drivers side battery firewall
as they are fairly cheap and known to fail after 10--12 years use ,rather regularly
Repair the harness as necessary.

191824d1264138110-maf-relay-differences-they-relays.jpg

They get mixed up after 30 years with the later 1986-87 MAF, & 1988-89 MAF Bosch part number specific MAF's.

The conditions for setting this code are:

no Code 21 or 22 (TPS Error) present, and
the air flow reported is < 4 grams per second, and
TPS indicates 10% or more throttle position, and
the engine speed is 1800 RPM or higher, and
the above conditions exist for over 5 seconds.

Typical causes for this code include:

1) Faulty air ducting to or from MAF sensor
2) Faulty ECM-to-MAF connections
3) Poor routing of MAF harness (i.e. near coil packs)
4) Maladjusted TPS sensor
5) Defective MAF sensor
6) Defective ECM

Grumpy · Sep 30, 2019

heres info on a similar code 34 fault thread

Pull the ECM down from the underside passenger of the dash.
Unplug the ECM and set aside.
With a wiring schematic for your 1985 Corvette find the MAF Power Feed , Ground wire to the MAF, & the MAF output signal wire to the ECM.
Computer harness side.
Unplug the MAF.
Test each connector terminal back to the ECM Plug terminal for continuity.
Should read near Zero Ohms each.
.1 - .2 ohms is OK.
Anymore you have a broken wire or a Green corroded wire.
Repair the harness as necessary.

They get mixed up after 30 years with the later 1986-87 MAF, & 1988-89 MAF Bosch part number specific MAF's.

Cardone remaned MAF's work.
I had to replace the MAF on my 1987 Corvette back in February.
Used an Advanced Auto Cardone Remaned MAF.
Runs Flawless now.
On these old cars the grounds sometimes get corroded or partially broken. I once had an intermittent caused by someone, years ago, sticking a 12v probe throught a wire. Over the years the wire corroded internally and would very occasionally cause problems. It was fun to find.

I would run a continuous ground wire from the case of the ECM to the black/white wire on the MAF and then to the Black wire on the burn-off module and then to chassis ground. Just route it out of the way and let it run like that to see if the problem returns. Since you've changed everything ........including the engine........I'd be tempted to believe you've got a harness problem and the ground is the most likely.

Or you can bite the Bullet and pay $450-900 for a GM NOS Bosch Hotwire MAF for C4 Corvette

MAF Code 34 Solution, 1987
Friends: I struggled with a code 34 fault in my '87 convertible for the last year. I cleaned and eventually replaced the throttle body (48mm to 52mm). I went to 52mm because you cannot get stock ones anymore, at least that I could find. I replaced the MAF sensor twice thinking "that must be it" but probably was not. The thing that finally made my screen run black instead of that stinking orange Service Engine Soon light was the cheapest fix of all. I replaced what, I am sure, was the original relay. It is an oval, plastic unit located on the firewall behind the battery. There are two there, one for the fuel pump and the other for the MAF sensor. After switching on and off internally for 25 years, they apparently get tired. And they cost $10.00! A ten dollar item can render a $300 sensor completely useless. It took forever to figure this out because the general wisdom is that it was something else. I would have saved a lot of money and time if I had recognized the importance of this little switch at the outset. Not every MAF Code 34 is going to be thrown because of a faulty relay. For ten bucks and 15 minutes worth of time, I would always start by replacing this part before digging into throttle bodies and sensor replacements. Since I was in the neighborhood, I replaced the fuel relay that was mounted right beside it just for grins. It was obviously the same vintage and I now know that if the fuel pump starts acting up, it's not a measly $10 part causing it. Just something to addd to the discussion for everyone. There is not a lot of mention of relays and their relevance, replacement, and diagnosis in the shop or 3rd party repair manuals. And, in my opinion, it should have been number one when dealing with a near-vintage car. Change out the cheap stuff first! Dave

Putting a new MAF on while using the old relays can burn out the new MAF. Always replace them both, especially if they are old.
Remember there are two MAF relays, a power and a burn off. I did the same thing, then replaced a relay and it was fine, problem came back and replaced both relays but havent driven the car since. Also the wires were all messed up, so be sure to check those for any fraying. For the record, no one at any of the parts store had a MAF relay, I ended up checking part numbers and found another relay to tell them what I wanted in order to get the part.

https://www.rockauto.com/en/catalog...witch+&+relay,mass+air+flow+sensor+relay,3584
The correct GM part numbers for the relays are. GM Borg Warner and GP Sorenson.

GM 10067925 MAF power
GM 10094701 MAF burn off
GM 14078914 Fuel pump

BW R3009 MAF power
BW R671 MAF burn off
BW R761 Fuel pump

GP MR22 MAF power
GP MR82 MAF burn off
GP MR5 Fuel pump

AutoWiz · Oct 11, 2019

I don't understand the hood on that Callaway. We restored one years ago back in my early days at vetteXperts. It got into boost fast and was a hoot to drive. Small turbos but they were water cooled. It was an 87 I believe and it had the 4+3 transmission. But it had these triangle cutouts in the hood to feed the intercoolers on the valve covers. They are missing from the white car in the above videos. I want to see better the underside of the hood of that car and understand if later year Callaway C4 cars had a different way of feeding air to the intercoolers. Here are a few pictures of the one we restored..

AutoWiz · Oct 12, 2019

I just cant get over that hood. Is that a stock hood on a Callaway? Because if so that is a major problem. Those intercoolers sit inches above the hot engine and bolt to it. There needs to be a source for fresh air to enter and cool them coolers. In this video is a 1990 Callaway and while a different shape for the later C4 there are still openings in the hood to feed those intercoolers..

And I am all for the idea of changing the MAF to a newer style. The maf in your car is a early design that was just a poor design. The newer design enjoys a very low failure rate and very high reliability and accuracy.

Re-manufactured Maf Bad? Code 34

cski68

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Grumpy

The Grumpy Grease Monkey mechanical engineer.

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The Grumpy Grease Monkey mechanical engineer.

AutoWiz

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