Droshki

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?

_twisted_

when you say pullthe MAF - are you just taking the connector of teh bottom or removing the whole MAF?

It sound like you have a bad MAF - and removing the plug gets you into open loop and it runs off the presets.

go to the local auto recycler and try to get a MAF of a 3rd gen or borrow one from a friend

Droshki

Both ways. Initially with it totally removed, and then later with it just unplugged.

MAF of off a 3rd Gen? What do you mean? Camaro?

And yes, I might be able to borrow one...might take a day or two though..

LarryK 87

yes, camero or firebird, they both work

RandyJ75

First off, please don't kill yourself. If you need it, I have an Auto Xray Scanner, PM me your info, and I will lend it to you. I think it works on an '85. One thing to keep in mind is that you could have a bad ECM, They can drive you nuts.

Randy

Muffin

Your FSM gives you a troubleshooting tree for code 34. Assuming you ran the tree, what were the results?

Droshki

Randy- Thank you- I will let you know if it comes to that.

Muffin- Not to be a wise ***, but if I had a FSM and ran the chart, I probably wouldn't be asking for help. Perhaps you could tell me the best place to buy a FSM, should it come to that.

On the other hand, this problem has been waaaay crazy intermittent and I have seen a code 34 only twice out of about 15 hours of troubleshooting, and I am not sure that I did not cause the code to be set by putting the car into/out of service mode with it running, car flaming out/stalling, etc. I mean really, I'm not sure the code means anything, its not repeatable at all. so going down that troubleshooting tree might not be....the way to go. I mean if it set 34 and it stayed, and it was repeatable.....sure, great, but that's not what I'm seeing.

I think the thing I am focused on is the finally, maybe the problem has decided to stay long enough to be troubleshot and the main symptom being that the car will not go above idle unless the maf is unplugged.
(Oddly enough, I have a 94 Chrysler that had a MAP go bad, and did this same thing, replaced sensor and it was fine). So, I need a way to test the MAF. My choices are going to be find a known good one to borrow ( or another car to put MINE in, in case it is my relay/controller box that's actually bad) Or...some way to view the output of the MAF....which uh? (really, one of these days I'm gonna get off my *** and get the laptop setup, but who plans on getting into this kind of stuff? not me!) I dunno, I dont know anything about scanners. Will this scanner that you are offering Randy, will it show the MAF voltage so I can see if it is present, changing and within parameters?

mykle

The tree says...

If the MAF is bad it should be throwing a 34 with the MAF connected if you run it over 2000 rpm in nuetral for a minute or so. It doesn't seem like you will be able to do that step, so i'm not sure how valuable knowing the next step will be. But...

...with the MAF disconnected run it over 2000 rpm for about a minute or until the service engine light comes on. Then check codes.

A 33 means replace the MAF
A 34 means look for a short to ground in ckt998 (dark green wire) or a bad ECM.

CFI-EFI

It DID come to that when you bought the car and decided to do your own work. Used FACTORY Service Manuals often come up for sale in the forum parts for sale/wanted section, on eBay, or they can be purchased directly from the publisher. It is difficult to believe that one could be a member of the forum for any period of time and not be aware of this.

RACE ON!!!

Droshki

... I respectfully request that you save it for someone else, because it is not useful to me.

Thank you for your understanding.

evmlarry

Just a heads up, these things don't like to always throw codes when they have issues. For example, let's say your MAF is the culprit, you may not see that 34 everytime. I have no clue why personally, but I've seen it happen with my own 85. I wouldn't completely rule it out.

evmlarry

Also, I think it may have been recommended, but you might even want to look into getting a cable and doing some data logging to find out what the car is really saying at each sensor. That might help out quite a bit too.

Droshki

Working on some suggestions from above, today I ran the car at 2500 RPM for about 5 minutes with the MAF disconnected, and also ran it for about 5 minutes at idle with it connected (cuz all it will do is idle with it connected). Neither test set a code. Interesting huh?

Then I was able to borrow a MAF out of an 87 and swap it in and the car ran great. I was also able to check the burn off function while I had it, (as was suggested by a member here) by looking into the MAF as I had someone shut the ignition off.

I stopped on the way home from returning the borrowed MAF and ordered one with a lifetime warranty for $185 incl tax.

I guess the lesson at the end of this very long post, that can now be useful to others in the future, --is that, in an `85 at least- a MAF can be way intermittent before totally crapping out, and- it does not necessarily set a code when it does go.

This is what I was looking for when I came here, real world empirical data and experience shared by others, not to just be told to go buy a helms manual.

I thank those that offered me support, suggestions, and their experience.

CFI-EFI

Although tempted, I didn't offer any suggestions.


And just who was it that told you to go buy a manual? I hope you are not referring to me unless you can show us where. I merely answered your question.

RACE ON!!!

_twisted_

you are welcome, now drop another hundred and go buy a helms manual.

sknight88

I just listed a brand new 1985 Helms manual on Ebay right before reading this post. It has a buy it now of half of what it sells for new. Take a look if ya want, best luck either way on your car, been thru similar on my 89.

Droshki

Sale complete....thank you very much Sknight

_twisted_

sknight88

Thanks, boxing it up right now for ya, Shawn