Back in October of 2000, at around 104K miles, the catalytic converter collapsed on my '94 Z28. This was the second catalytic converter to fail, the first occurring at approximately 26K miles. Considering that it could no longer breathe, it would barely pull itself along. I had a new cat put on and witnessed my car running fine after the old cat had been cut off. After the new cat had been mounted and I went to pick it up, it was running just as before whenever I tried to give it some gas. I figured that some of the cat had blown back into the exhaust and that it still couldn't breathe. Based on a number of factors, I ultimately decided to put it in storage, in my father's garage, and purchased a Grand Cherokee.

I got it out of storage over Christmas this year in hopes of getting it running. Here is a sequence of events.

1. New oil & filter.
2. New fuel filter.
3. New air filter.
4. New battery.
5. Disconnected the catalytic converter from the exhaust.
6. Put a little gas in the tank.
7. Try to start it, nothing.
8. Determined that it wasn't getting any fuel.
9. Dropped the gas tank and installed a new fuel pump. What a PITA. I think engineers should be forced to work with some mechanics when designing an automobile. Old pump had definitely given up the ghost. Sending unit also appears to be bad, but I didn't feel like dropping 250-350 just to get the gas gauge working. I'm hoping that maybe the gauge is just stuck. If not, I'll just have to be careful not to ever run the fuel low.
10. Tried to start it again and it fired up, but was running horribly. Sounded like it was only firing on a few cylinders.
11. Checked plugs & wires. They looked good and I seem to recall having them changed not too long before putting it in storage.
12. Changed differential fluid & gasket.
13. Changed transmission fluid.
14. Borrowed a friends automotive stethoscope and checked the injectors. Determined that only two of them were working. So, we theorized that the reason it was running like crap was because only two cylinders were firing. Began checking voltage to the connectors to see if the injectors were getting any fire. About this time the starter went out.
15. New starter.
16. Determined that the non-functioning injectors were getting some fire.
17. Took off the fuel rails and replaced all eight injectors.
18. Cleaned throttle body and intake manifold.
19. Attempted to start it again. As soon as fuel got to the rails, it fired right up and was running much, much better. It still has a sputter at about 1500 rpms when not under load. Otherwise, it idles and revs pretty good when not under load.
20. New thermostat.
21. Tried to drive it and thought it was going to explode. Sputtering, misfiring & backfiring. Oh My.
22. Had the codes read and there were only two, which was kind of disappointing as I was expecting several. I can't remember the precise codes. I have them written down, but they're in Kentucky, with the car, & I'm in Michigan. One indicated a low manifold air temperature and the other indicated a malfunctioning Mass Air Flow Sensor.

That's pretty much where things stand right now. I had to come back to work and I left the car in Kentucky in my brother's shop. Plus, I couldn't really afford to sink anymore money into it right now. All in all, I think we've made pretty good progress. It was kind of fun doing all of that stuff, although my brother might disagree. But, it sure beats paying someone else.

The mechanic who read the codes seems to think that the MAF could be causing most, if not all, of the issues with the way it's currently running. My plan is to next replace the MAF and the O2 sensors. I'm thinking that the O2 sensors, combined with a bad MAF, could be causing it to run rich, which could explain the issues I've had with catalytic converters. I'm also considering new Air & Coolant Temperature sensors.

I'm guessing it could also need a new Optispark distributor, but I'm holding off on that in lieu of replacing cheaper things first. I'm also wondering whether the ECM could be bad. The mechanic who read the codes, and only charged me twenty five bucks, thinks it's unlikely that the ECM is bad and felt strongly that the MAF was my biggest problem.

Are there any affordable OBDI readers on the market? We tried to cross the ALDL, but didn't get any codes. The fans came on and that was about it. Could that be a sign that the ECM is bad?

So, can a bad MAF make it run so bad under load that it's undriveable?

What would you do next? Any input is greatly appreciated.

 

Change your transmission gasket if you have not already. Mine sat for only a year and now it's leaking.

 

Easy to rule out the MAF, disconnect it and try to run it.. if it clears up, may have found your issue.

 

It seems to run about the same whether it's hooked up or not. But, I didn't actually try to drive the car with it unhooked. Will these engines run OK if the MAF is completely non-functional? If it's doing nothing, would that be synonymous with having it unhooked?

My car is a 6-Speed and my service manual is also in Kentucky. Do those have gaskets on the transmission?

Are the actual factory service manuals available for these cars? The Haynes manual I bought was OK, but probably pales in comparion to an actual FSM.

 

If it's giving false information when it is hooked up the car will run like garbage.

The car should drive fine w/ the MAF disconnected. If there's no difference then the problem is not the MAF. Service manuals are available, check ebay.

This is a great deal, here ya go:

http://cgi.ebay.com/ebaymotors/1994-...68465499QQrdZ1

 

I'm wishing I would have tried driving it without the MAF connected, but I didn't think to try that. I'm wondering whether the MAF is providing any feedback at all. I could have my brother unhook it and try to drive it. It seemed to make no difference when we were messing around with the engine and it wasn't under load.

Thanks for that link.

 

Yep, load makes a big difference, so no way to tell as of yet.

 

With the scanner hooked up see if you have any MAF readings and look to see if it seems to be reading normal, same with the other sensor. Also clear the codes, and see if they come back right when you start it up and try and drive it. If it does, you more then likely have a problem with those. Take a look at the wiring, if it checks out looks like it's time to fork even more money out.

 

my car had a miss and stumble around 2k and it was spark plugs, so maybe try changing out plugs and wires. My plugs looked fine, but i changed them while i had the old ones out, and it runs 150 times better

 

mine ran like that when one of the wires to the map was slightly severed. make sure its getting the right voltage. i'd also say to make sure all electrical connections are good and not chewed up. i know this the hard way (rabbit chewed them, but i got my revenge)

 

Mine ran horribly until I replaced the Opti, might want to give that a shot. If not maybe somenew O2 sensors.

 

I feel that the MAF is probably bad, so I'm planning to replace that, along with the O2 sensors, before replacing the distributor.

I've seen mention of a Guanatella, I doubt that's spelled correctly from memory, MAF. What are the advantages/disadvantages of it over an OEM or OEM replacement? I also looked at some distributors on RockAuto.com & SummitRacing.com. Rock Auto doesn't appear to carry MSD. I'm not sure which one I would need, but I'm thinking this one. What's the difference in pin driven and spline driven? I've purchased some factory service manuals off of EBay. That should help in my education. I'm also interested in some distributor setup called LTTC that was mentioned on another site. I don't know much about it at this point, other than it supposedly reduces the risk of the water pump ruining your distributor, or how much it might cost. I guess this car is going to be become a hobby, but I would like it to remain pretty much stock, street legal and driveable on a daily basis. I also don't want to sink my life savings into it. I have a lot of work remaining, including some body work.

Where does everyone here get their stuff? Local auto parts stores, internet, both?

 

Man does your story sound familiar, my car has been in storage since 2001. I think the oil pump died and wiped the bottom end. Anyway, many $$$ later it runs but much like your car has issues. I too had to change the fuel pump and injectors. My problem is similar in that it seems to run fine when not under load. When you try to drive it you get a loud popping in the exhaust and the car stumbles. I'm going to try to disconnect the MAF as someone suggested. Also, do you know if a bad O2 sensor will cause a code? Plus, my check engine light is not on so I guess the ECU is not throwing any codes.

 

If I had it to do over again, I would have drained the fuel system before letting it sit. At the very least I would have relieved the pressure in the lines.

When we first got my car running the oil pressure seemed fine. But, after changing out the injectors and getting all eight, or most of the eight, cylinders firing, the gauge wasn't reading much more than 20lbs. I'm hoping it's the sending unit and not the oil pump.

Other than the expense, it's been kind of fun getting the thing running. If I had known what I was getting myself into, I probably could have saved some money. I didn't foresee doing much more than cutting off the exhaust, changing the oil, putting in a new battery and firing it up.

 

Well no dice for me... the MAF was nasty!!! Cleaned it, car runs great until it warms up then starts popping (under load), tried it with the MAF unplugged same deal. Did you replace your O2 sensors? If so, did they throw a code? I'm not getting a check engine light.