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  1. #1
    Electronic Ignition!
    Join Date
    Feb 2014
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    13

    TPI MAF Sensor Degradation

    I have a 1227165 MAF TPI on a 72 chevelle. It runs nice when the maf works. They last about 10 hrs and then give max gm/s at idle and make it run super rich. At idle it shows 23 gm/s instead of 5.5 – 6.2. It gives a code 33, max MAF value exceeded. I’ve gone through about 5 Cardone remanufactured MAFs. They run great , then fail.

    At startup it either works right, or fails. If it starts as right, it stays right. If starts as fail, it stays fail. It does not start right then degrade to failure when driving. It never starts a failure and then becomes good. If failure, I have to start by using 1/4 throttle and slowly let up. The MAF when new works great consistently. Then over time, every so often it starts as a failure. Then the occurrence of a rich start becomes more often. After a while, it fails all the time. My wb O2 shows the mixture getting richer below 10 AFR as it slows to idle. It is so rich it barely runs. At higher throttle it goes so lean it doesn't have any power. It says 23gm/s till a higher rpm then jumps to low 40’s gm/s and varies a little. It never reaches 50. As rpm goes up, it gets leaner till past 20 AFR. Sometimes this was intermittent where it would work normal showing 5.5 - 6.2gm/s at idle and run great. Then start it again and it acts up. Now it is acting up all the time.

    If I unplug a failing MAF, the car starts and runs. It’s sluggish transitioning. You can see the calculated maf values while data logging. The BLMs take a while to adjust. Sometimes there is much less power till the blm catches up. I can get home this way.

    Conditions:

    I have a Painless harness. I soldered the harness ground wires to a 10 gauge battery cable accessory line so it is direct to battery. The 12V terminal is soldered to the harness and attached to the 12V above the power brake booster. I have a 3-wire electronically regulated alternator and tunerpro displays 13.9V nearly all the time. At idle it will drop to 13.6 sometimes. The battery is about a year old and starts strong.

    I tried 3 1227165 ECMs. The latest was a Cardone remanufactured. All work the same.

    I replaced the 3 relays w automotive 30A epoxy sealed relays. I swapped out the relay sockets by soldering them in and heat shrinking the joints. Dissecting the factory oval and rectangular relays showed a sloppily built relay where sometimes the contact barely had pressure or a small gap since the relay metal frame was poorly shaped. The factory relays have a resistor in parallel w the coil. The new relays are coil only.

    Using a volt meter I verified the fuel pump, maf, and burn-off relays are working properly. Also, MAF burn off works because after turning off the engine, I quickly ran over to see the wire glow red hot. I can hear the relays click each time I turn on and off the key. You can hear the maf burn off click then a second or two later click again. Failing MAFs glow for burn-off as well.

    Research:

    An author claims the 1227165 was superseded by 16198259, then by 99888194. He says changing to 88999194 fixed this issue. He says the 165 stresses the maf each burn-off cycle and the 194 doesn’t. (He incorrectly typed 99888194.) http://www.corvetteforum.com/forums/...ay-issues.html

    Has anybody heard of this? Has anybody used a 88999194?

    Reflection:

    So why do these MAFs keep failing? Is my system stressing it? Is there something I can check?

    If my system is fine, what can I do to substitute a more reliable maf?

    I found a ford analog maf from the mid 90s. I doesn’t have the burn-off and looks like it would work w 3 wires. On the web I found a doc that shows a similar response curve as the bosch. I was thinking of this as a replacement. Downside is this requires making a custom housing to fit in the 3” air tubes.

    I was also wondering if the LT1 or LS1 mafs can be tapped before the analog to frequency converter and and analog output made? These would be modern, cheap, and allow more flow. I assume much more durable.

    I’m sure others have hit the same wall as me. It would be nice if someone has this figured out.

    Thanks for your help,

    TPI Chevelle
    Last edited by tpichevelle; 08-10-2015 at 09:25 AM.

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