19875speed

iTrader: (2)

My check engine light came on and a code 36 is coming up on a 89 tpi 305. It says it could be 3 different things.

1. MAF sensor burn off circuit problem
2. Direct ignition system fault loss of 24X signal or extra or missing pulse in
EST signal
3. Ignition system fault loss of high resolution pulse signal

The car seems to be running fine, don't know which of the 3 it could be and is it something to worry about?

Vader

If this is for an '89 TPI, there is no 24X distributor signal or high resolution pulse train. That only leaves the MAF burnoff.

This can be cause by MAF circuit connections at the MAF or the MAF power/burnoff relays, problems with the relay contacs themselves, or the oil pressure switch. Rarely is it a problem with the ECM, but that is a remote possibility.

19875speed

iTrader: (2)

Thanks for the help! Would changing the MAF sensor fix the problem?

Also the problem started after I got it back from the garage. they put a custom chip, new t-stat, set timing and installed polished runners, plenum and TB. It seems every time they work on it they mess up something else.

Red Devil

Damn Vader.. still around and confusing people.

It's almost always the relay. No, changing the MAF will not fix the relay issue if that is what it is. You can likely swap around relays (I can't clearly remember) to test. If it's not the relay, then bug Vader, he knows hit ****.

ASE doc

Where did you get your code information? 36 is most definitely not caused by the MAF sensor. Code 36 sets for the lack of a burn off signal after engine shut down.

The ECM activates the burn off relay for about 15-30 seconds at engine shut down, after a certain amount of run time. When the ECM doesn't see the burn off signal through the MAF sensor, it sets code 36. Start your diag by checking connections at the MAF sensor, MAF relay and MAF burn off relay.

There is a trouble tree published by GM for each of the fault codes. The trouble tree gives fairly simple step by step instructions for pin point testing a fault code to find the exact cause. I don't know for sure, because I don't use anything but the factory service information, but I would guess that even a Hayes manual has these trouble trees. The trouble tree testing for code 36 only requires a 12 volt test light.

19875speed

iTrader: (2)

Thanks everyone for the info! Got the code info out of a book that came with a cheap scanner from an auto parts store. I didn't understand what that code meant until you guys and someone else explained it, I'm still learning the ins and outs of the TPI system.

Vader

That's O.K. I've had a TPI for a couple decades, performed a handful of TPI swaps to older ('50s-'70s) cruisers, built the harnesses and done the programming, repaired more than i can remember, and sent out custom PROMs, and I'm still trying to figure it out.

Doc's description is spot-on. The reason I mentioned the oil pressure switch is because that's the signal to the ECM to begin the burn off cycle. If the switch is intermittent it interrupts the cycle and sets the code. I encountered one of those once and will never forget it, although all the pulled-out hair has since returned.

One thing to note is that the burn off cycle does NOT occur at every engine shut down. Trip timer and number of starts factors into when the cycle is run. The ECM will look for a maximum MAF signal during the cycle to prove the burn-off was successful. If the connections at the MAF are poor, relays are unreliable, or circuit connections are faulty, the code will also set.

If the MAF itself were bad the ECM would tell you right away, since it only tolerates a MAF signal out of range for 600mS. Control is pretty tight that way.

The relays are the easiest thing to check, and in some years you can simply exchange the MAF power and burn off relays to test this. If the relay part numbers are the same they can be exchanged, but if they are both failing you may not learn anything. If you do this and clear the code you may have to wait several days to see if the code returns. Happiness is not instantaneous with this part of the system.

Another thing to note is that BOTH relays are necessary to complete the burn off since power to the MAF is supplied through the NC contacts of the power relay to perform the cycle.

ASE doc

Thank you Vader for clarifying the OP switch's role in burn off function. I was not aware of that, or if I ever was I forgot. The trouble tree as is often the case, over simplifies the diagnosis. It instructs you to clear codes, run the engine til closed loop is achieved, then start the engine and run it for 20 seconds or until the code returns.

The trouble tree is a good place to start and it generally gets you to cause of the fault. This isn't always the case. Sometimes it takes more digging and more time.

If you're going to diag and repair your own vehicle, I strongly recommend you invest in the factory service manual from Helm's Publishing. It offers the very best coverage of all systems on a GM vehicle. It includes an electrical diag manual that is priceless for diagnosing all of the electrical systems, including EFI, on our cars. The Helm's books sell for about $125.

If that is not practical at this time, try a Haynes or Chilton manual, if you can find one for your car. Another option is All Data. All Data is a professional technical information service that provides reprinted(web based) factory service information for vehicles as far back as 1982.

I don't know about all libraries but in Multnomah County, Oregon, All Data is available at the public library. You may also be able to purchase a limited subscription for home use. I've never looked into this but it's worth checking out. All Data coverage on the 3rd gen is pretty good.