Settle in- get yourself a fresh beer and some popcorn.

For the record: this is my 1985 and the ZZ4 was installed a couple years ago by the PO and Ive really had no trouble with the car till now. Its NA, dont get confused if you read my profile, its my 76 that has the blower, not this car. Ok, here we go....

6 weeks ago: Car driven about 1 hour. Shut off for 10 minutes, would not restart. Sounded like it was hitting during the crank cycle, but not when key let back into run position. After much cranking and wtfing, went and got a gallon of gas. After some cranking and bleeding at the shrader valve on the fuel rail, car started right up and ran like a champ. Although ¼ tank indicated, car takes about 14 gal at the gas station, so I figure, inaccurate fuel gauge, Ill be more careful next time.

3 weeks ago. Car driven 15 mnutes. Sits about 20 minutes. Will not start with same syptoms from above. Have car towed home. (Car has ¾ tank). The next morning before I touch anything, I try to start the car. Starts right up, no problem. I remove the ignition module and have it tested (good) but replace it and the condenser anyways, figuring, they are relatively cheap things to rule out.

2 weeks ago. Car flames out while driving, but immediately restarts. 2 days later, it does it again, but does not restart. 3/8 tank indicated ( this really seems to drop the more you crank on it, perhaps the battery voltage drops? The indicated level dropped during the 6 week ago scenario too). Anyhow, believe it or not, I get a gallon of gas and pour it in and the car starts right up, and I drive it home, hiting in excess of 4300 RPM to check if its running OK.

Now, Im like—there has to be something funny going on in the tank, because one gallon of gas is NOT fixing the car. I think back and the last time I added the gallon, the gas cap made a big woosh when I unscrewed it..so I start to wonder. I removed the charcoal canister (because everything wasn’t hooked up anyways, and the headlight was hitting on it, I mean it was fubared before I got to it) and plugged all the lines like 4 months ago…and no problems till recently,,,but still…who knows for sure. So, I drill me 2 little holes in the gas cap- insta tank vent, in case I am pulling the tank into a vacuum and removing the gas cap is whats actually fixing the problem.

Off I go to for a test run…get less than a mile and a half, car flames out….I manage to get it restarted in gear and limp it home, car will not go over 600 rpm. After I get the car in the garage, I note that it will rev up with the diagnostic connector jumped, but not when its not. For a while anyways, Then it wont rev past about 6-700 at all. I get a code 34 during all of this, but who knows if it is because off all the dying, restarting, and whatnot- I don’t read too much into it.

Im pissed now. Out comes the fuel sender and electric pup. Sure enough the screen on the pump, the sock is collapsed and you can see where its been sucking down and blocking flow (probably anyways). Replace sock, and replace fuel filter down at the frame rail for good measure. Start car. It will not go past idle (6-700) without dying. Install fuel pressure gauge. 40 PSI.

Now Im like really, WTF. So I pull the plugs. They are all carbon fouled bad. Replace plugs. No Joy. Replace cap and rotor, and find cap button that rides on rotor is way worn out ( only like a year old wtf some more) and in fact shows signs of arcing because it really cant reach rotor. Ok, so new cap and rotor. Test drive hard accel up and down local road 6 times, and around neighborhood. No problems. Finally problem solved. Right? Of course not, this piece of cr&p. I took it out today about 5 miles away, ran great, turned it off, it sat for about 1 hour, and when restarted went into its "not going past idle" mode. After getting it rolling in gear at idle ( by starting it in gear) I decide I can not limp it home like this, this time, its too far. Last time I did it, I was only like a mile and a half away..this time Im like 6 miles away. So, I get out my handy dandy paperclip and put it in service mode. Car runs like a raped ape all the way home. In the garage, runs good in service mode, but wont go past idle w/out paperclip. Run codes, Code 34. Fine. I remove the MAF sensor. Car runs amazingly well without it. Wtf. Computer must stick in a value. But Im tempted to just leave it out. Put MAF back in-car wont go past idle, Pull MAF out, Car runs great. Find the following on Corvette fever website:::

The '85 Corvettes do not use relays for the MAF, but instead use a module next to the ECM. This module rarely goes bad; but to check the module on '85 Corvettes, look for 12 volts at connection E on the MAF with the engine running. Then, run the engine for at least 5 minutes, turn off the key, and check for 12 volts at connection D (MAF burn-off).

Good voltage on E. Very questionable voltage on D for burn off, but I don’t think burn off is really my issue at this point, do you? Interestingly enough., there is a weird chatter under the dash during the burn off cycle that I noticed the other day but have never heard before. I pull the dash apart ( can you believe I’m still with this and haven’t pushed the car over a cliff?) to find the control box. It must be the big thing that says Bosch on it and clicks when its burn off time, but that’s not where the chatter is coming from, that’s coming more from the center of the dash. But screw it…I mean who knows if the burn off will even work right, the MAF is still unplugged. I think Im getting sidetracked.

Anyhow, as I write,. Im clearing the codes again. Have I proved bad MAF? Jesus they are expensive, Id like to be more sure before I spend 200 bucks. Be a good time to have a laptop and the program to look at this car and see what the MAF is actually doing wouldn’t it? But I don’t. Suggestions? Anyone local to me that has a way to scan what the MAF is doing? Or do I just go by a MAF and hope that’s it?

OK just went out and checked one more time. Connected MAF, cleared codes, started car, Will not rev past idle out of service mode or even when in service mode now. Unplug MAF….car revs up fine (actually little backfiring now,when I really rev it, but nothing too radical)


So…help? Should I just kill myself?

much as im sure you dont want to hear this, it sure does sound like the MAF is shot.
you should be able to find one on ebay for a reasonable price, i bought one as a spare for 75.00 a few years ago.

No, i wouldnt go to say MAF is shot at all yet, its very likely, but its certainly not a certainty yet.

The issue as you stated of being able to usually run fine all day then stop it and it wont restart, that is probably the MAF Burn off causing that for what ever reason, that silver looking piece you found in the dash with Bosch written on it is the relay. My 87 did that same thing ages and ages ago, and replacing the burn off relay fixed the issue, it would start though when this all occured, it was just extremely hard to start, where as normally it would start very quick and easy.

If you can get hold of another MAF to check in your car, or even check your MAF in another car, this will tell you if its ok or not.

I think youll find that Bosch relay in the dash is a very expensive item too.

Gee... I like the MAF controller problem, too, but with the heat related failures, I wonder if the pump isn't failing. Considering it sucked up the in-tank filter, I can't believe it's 100% right.

Well i had considered that myself as well, however if indeed it was a pump failure issue, id be rather positive it would do it with or without the MAF connected.

Agreed. I would test the MAF and see if it happens regardless.

Yeah, best way i know of to test a MAF sensor is in another car that uses the same sensor, and that car being known to run perfectly well with its own MAF

absolutely.

My only worry is if the MAF controller is bad, could it hurt the MAF??

Yep, the 85 system is different to the later models. Its got that relay/module in the dash instead of the other 2 cheap relays.

And i was saying earlier if that relay/module in the dash is rooted, that could explain the running fine and then difficult restarts, i certainly wouldnt say its out of the question. Those Bosch relay/module parts should be very reliable, but we are reffering to a part that has potentially given as much as 23 years of service, and unless there is proof its been replaced, we much assume that is hasnt and its the piece that left the factory with that car.

P.S. mate i just re-read that line, i am not sure if you mean hurt the MAF as in hamper its function, or as in damage it, if its the later, i dont believe it could, but then i dont really know for sure.

I was saying "hurt" in the sense of damaging a good part. I donno if it could do it, but it makes me wonder. I guess it would require it to shoot more voltage in than it could handle...

but in the other sense, it would make diags that much harder, cause the problem would remain. Where to turn next? Fuel pump or MAF module?

Wow, thanks for the replies all, I had checked out of the site for a while and was surprised to see them.

As far as the fuel pump, I ran w/ a fuel pressuer gauge taped to the windshield for quite a bit. 40 lbs usually- sometimes dropping to 35 as I come (hard) off throttle.

Im kinna of the opinion that 1. I had all sorts of little maintenance problems like the sock that may have been part of the problem or not, but now 2. We are down to the fact that the car dont run with the MAF connected, and it does run with it disconnected. I know where an 88 is that they guy might lend me his MAF, but I might be better off puttng MINE in his car...in case as was discussed above, the Bosch control box ate it. Id ato have to replace his too.

The problem has just been soooo intermittent. If it would just stay broke, it would be a lot easier to throw parts at it, as much as thats not my preferred method.

Id sure like to know more about the theory of operation behind the control box to check it out, cuz yes I saw a price on one somewhere and it was like $500. For the moment I guess I am on hold...till I buy, borrow or steal a AMF....

No worries mate, hope our replies help you out ;)

Yep, do that mate, whack your MAF in his 88 and as long as his car is running fine, it will tell if your MAF is good or bad.

The intermitent factor is what leads me to believe its the relay/module, its hard for me to swallow the fact a MAF sensor could work fine and then be stuffed 10 minutes later simply cause you stopped the engine, and yet it works fine abit later on.

The fact it wont work at all now with the MAF doesnt really indicate the MAF is no good, it could still be the relay/module has failed completely, in which case the intermitent factor will no longer be part of it.

The fuel pressures you indicate there are fine, the drop off you see when getting off the throttle is the pressure regulator lowering the pressure, its controlled by vacuum, and when you get off the throttle, the amount of vacuum increases. The more vacuum in the manifold, the less resistance there is for the fuel to flow from the injectors, cause the vacuum will help to draw the fuel through, hence requires less pressure to flow a simular amount.

Interesting tidbit there about the fuel pressure, thank you- makes a lot of sense!

OK, so I was able to borrow the MAF out of a 87. Couldnt just stick mine in his car...because....drum roll.....the 87 hasnt been started since 2002!

In the end though, it made my car run great, and I was able to check the burn off function by looking into it when the car was shut off as was suggested to me by someone. I stopped at the auto parts house on the way back from returning the borrowed one and ordered one with a lifetime warranty for $185 w/tax.

Interestingly enough, I did some more testing earlier today and the car never set a code- running at 2500 rpm with the MAF disconnected, and also idling with it conected (cuz thats all it would do with it connected). Neither test set a code, so I guess the moral of this story is that a MAF can die without setting a code.....in an 85 anyway.

Great stuff mate, at least you found the right part to replace rather than check throw a few in and hope for the best

i had an unfair advantage,
1. my MAF did the same thng.
2. I had a spare MAF to test with
3. I Read his other posts on CF about this which was a bit more lengthy, even though it was intersperced with the usual moronic no help replys

Don't take this post as that I have a clue, because I don't. My only worry would be that disconnecting the maf would put the car in a "limp home mode" or open loop mode, in which there are other sensors that get ignored. Possibly a bad o2 sensor or something like that, then when you disconnect the maf it ignores it and it ignores the o2 sensor and others. If the new maf doesn't end up fixing the problem I'd think that is the case. (not that the o2 is bad, but that the car goes to limp home mode when the maf is disconnected)

[quote]Settle in- get yourself a fresh beer and some popcorn.

For the record]


You must be a pilot!!