While cruising the freeway yesterday, the Engine light came on and I noticed a slight impact to runability. When I got home, I checked the codes and found both 33 and 36. From the research I've done in the archives, it sounds likely to be the MAF burnoff and/or power relay(s).

I'm wondering if anyone knows what might cause the relay(s) to go bad? Is maybe the MAF starting to go south and causing a problem with the relay(s)?

A few years ago, I replaced the relays while trying fix an idle problem I thought was MAF related, so they were not 20-year old parts on my 87.

Granted, the relays are pretty inexpensive, so I'll probably try that first, but just wondering what might cause the problem in the first place?

Thanks!

 

wiring, MAF, relays, and as a last resort the ECM (but that is almost never the culprit)

Having bad relays can kill a MAF but it usually doesnt work the other way

 

Why replace parts blindly with no idea if they are bad or not? It's the same deal with replacing what worked for someone else. All you end up doing is throwing money at the problem. Follow the trouble shooting charts in your FSM for the codes set and FIX the problem, rather that assault it with a bunch of unnecessary parts.

RACE ON!!!

 

Hey, you live close, I now live in Auburn, West Hill. If you ever want to scan it let me know. Regarding the relays..if you have the FSMs read paragraph 2 on page 6E3-A-42. Been several posts regarding the quality of relays, I've had good luck with the ones I've bought from NAPPA. Poor connections or dirty connections at the relays can cause the codes to be thrown also. I'd check those first, second I would pull the fuel pump relay and check the wires going into it...on my 87 the insulation had schrunk back an inch or two exposing bare wires that actually came into contact with one another..not only bad..but dangerous (fire hazzard).

 

http://members.shaw.ca/corvette86/Code%2033.pdf
http://members.shaw.ca/corvette86/Code%2036.pdf

 

Isn't our friend from the north great, OK, read the second paragraph of code 33

 

Because, as usual, it's an intermittent problem. Some days it runs fine; other days, the SES light will come on during each trip during the day. I have the FSM and the first test tells me it's an intermittent problem (that is, I clear the codes, startup the engine and let it run for a while and no codes), likely due to wiring. From what I checked, the wiring looks OK, but who knows... wiring can be difficult.

Being a packrat, and all, I still had the original MAF relays, so I put those in and took out the ones that were made in Taiwan.

Like Rick, I checked the fuel pump relay and found several exposed wires. Rick (or anyone) have experience replacing a connector so that the wires are no longer exposed (or maybe there's another remedy).

I guess I'll see if the Codes 33 and 36 appear during the drive tomorrow... sigh.

 

I just carefully removed the pins and bare wires from the relay connector, slipped on some shrink tubeing, hit it with a hair dryer and reinstalled the pins...worked for me.

BTW, I only did one at a time..so I got them back in the right order...the pins come out fairly easy and I just slipped the shrink tube over the pin...didn't disconnect the pin from the wire.

 

Sure enough, the SES light came on again today. Sometimes immediately, sometimes after 15 minutes driving. I guess I'll have to keep trying the diagnostic process and hope that the codes set so I can proceed down the tree... all the wires look good.

I read somewhere about the orange fusible link from BAT to the ECM, is it a simple connector I can unplug to reset the ECM? If so, any tips on where to typically find the connector?

Thanks!

 

You can reset, or clear the codes by disconnecting the negative battery terminal for a few minutes. You also may want to clean the terminals on the power tower behind the battery...just look, you'll see it, has several wires attached to it..some are fusible links. I've never experienced a weak fusible link, for me they've either been good or bad.

 

If a code 36 is thrown, test the relay like is mentioned in Agent86's links.

The relay is easy to get to. Here are my instructions:

Take off the cars side panel to access the battery.

There are 3 torx bolts at the edge of the fenderwell, a 10mm bolt on top towards the door, and there is one 10mm bolt you have to loosen at the bottom. This one you have to use the open end and go through the gap between that panel and the one below it. Just get it loose enough to remove the panel.

Remove the battery.

Disconnect both cables. There is a 13mm bolt that holds a piece of plastic down that keeps the battery stationary. Remove it and the piece of plastic. Now take the battery out.

Identify the relays.

Directly on the firewall behind where the battery was there are two relays right next to each other. The one towards the outside of the car is the MAF power relay, and the one towards the center of the car is the MAF burnoff relay. If your relay is bad, a new one is about $11.

Cleanup.

All the stuff I told you to remove goes back on the opposite of how it came off, there aren't really any quirks. If you haven't taken any panels off the car before, you have to line it up. With the drivers door closed, but with the hood still up, put every bolt into it's spot and have them to where you can move the panel about, once you get it nice, tighten them all up.

Good Luck,
80sRule

 

Thanks for the instructions... those are always great, especially if you've never done it before. I was lucky enough to be able to squeeze my hands in above the battery and remove the relays without removing the battery.

Anyway, I tried the diagnostic testing again tonight (limited time). I cleared the codes (by removing the negative terminal of the battery, but I *hate* doing that, cause I lose all my stereo settings... sigh), then started the car and let it idle for a minute (no code 33), so I ran it until my laptop software said it was closed loop, then shut it off, waited 20 seconds, started it back up for 30 seconds (no code 36). I don't have the time tonight to proceed as though the code had been set and test the relays. I guess I'll have to keep trying until the codes set during testing.

 

If I understand correctly...you removed the relays..then reinstalled them, after clearing the codes, and now it's not throwing a code? perhaps by pulling the relays you inavertently cleaned a terminal?

 

Sorry I wasn't more clear... I'd be happy if that was the case--I'd think I'd solved the problem! A few years ago, I replaced the MAF relays, but kept the original relays. A couple of days ago, I put the original (GM parts) MAF relays back in (taking out the replacement parts).

I then tried the diagnostics process, but didn't get either code. I've done this on two different days, now... the SES is on most of the day; I get home, have dinner and hit the garage for some testing. Disconnect the battery to clear the codes, then start it up to see if it sets a 33 or 36, but nothing... sigh.

While driving the next day, I get the codes again. Today, actually, I had the laptop in the car with me, while driving to work. After about 10 minutes of driving (about 5 miles), it suddenly died while sitting at a stoplight. When I started it back up, the SES light came on; I used the laptop to detect a code 33 (but no code 36). After shutting the car off for a couple of hours, while I went to an appt., when I started it up, the SES light came on immediately; checking the codes this time showed both 33 and 36.

Maybe I'll have to try the diagnostics testing right after I get home... which would imply the problem is related to whether the engine is warm or cold.

 

It wasn't on the chart of potential problems for my 86 when I had a simular problem, but my re-occuring mass air burn off problem was the MAF itself, even though the wire glowed red on shutdown, and the other things checked ok.

 

Don't know about an '87 but on my '89 there's no need to disconnect the battery to clear codes. Just pull the ECM fuse and then put it back in, simple no?

 

Ahhh... simple... yes!
But, I can't find the inline fuse on the orange wire leading from the battery. Oh... maybe you mean in the fuse panel? I'll have to double-check that... I don't recall a fuse for the ECM in the fuse panel.

 

This is good to know, LT1GMC, although I have to admit, I was afraid of this possibility.

How did you discover it was the MAF? Were you able to diagnose it? Or did you just come to that conclusion from trial-and-error?

Thanks!

 

If the post that Agent 86 didn't help. You need to get a scan tool and see how much flow in g/sec vs RPM, the MAF is sending to the ECM. Sounds like you need a new MAF. There not cheap and you need to make sure it's bad before spending the money. It could also come down to wiring or connections. Double check 'em .

 

Hmmm... I can see how that would be valuable to check. Is it possible to check the flow rate the MAF is sending to the ECM with scanning software? I'm using an old DOS version of DataMaster and it will show a table of flow vs. RPM... but not specific numbers (more like categories).

Is there other software I should be using that will make this kind of test easier? It sounds like I need to keep the laptop in the car and hooked up and ready when the SRS light comes on.

I have some software on a newer laptop that I'm using for OBD-II; can anyone recommend software that can read both OBD-I *and* OBD-II? If not, I'll just have to get some Windoze-based software for OBD-I on my newer laptop (I have a special cable on the way that completes the connection between the ALDL and the USB port on my laptop).