Hi All--I just spent a lot of time reading threads and couldn't really find one that fit my situation. Hope somebody can give me some ideas.

My 89 has 53k and has developed an intermittent really rough start and will then stall. After a couple of these starts it will then start right up and seems to run fine. It will do it hot or cold but seems to do it more often when cold. Sometimes it stalls while running down the road. It will start, but coughs and sputters like an old car with the choke stuck. It will also blow out some blackish smoke and exhaust smells really rich. It keeps tripping trouble code 34 which is MAF. This has been replaced twice. Also replaced MAF burn off relay and Intake Air Sensor. I have replaced fuel filter, dist. cap, rotor, spark control module, coil and checked for vacuum leaks. It's been a while, but I cleaned the throttle body and IAC a few months back. I replaced TPS at that time.

After reading several threads and responses, I'm thinking I should replace the injectors. Anybody else have any ideas? I'm about to start pulling my hair out but I don't have too much left and would like to keep what I have!

Thanks to all!

 

Does the car have catalytic converters?

 

I deleted the cat last year when I put on new exhaust system. O2 sensor is upstream and has never tripped a code.

 

Since your year came with Multec injectors, there is a good chance that they are the problem. Ohm them hot and cold, your looking for around 16 ohms.
Did you check out FIC's sticky at the top of page ??
How is your fuel pressure ??

 

I did go through the stickys. What a great resource. I printed some of the materials to go with the FSM. That's what makes me think I need to replace the injectors. I plan to contact FIC on Monday. They're not far from my house. I have a boatload of tools -- but not a fuel guage. I plan to go get one today and check pressure and I'll ohm out the injectors too.

The big thing that's driving me nuts is that it will run great at times and then out of nowhere it will do this rough start thing or stall while riding along. I'll roll to the side of the road or slide into neutral and turn the key--it will fire right up and I'll be on my way. Every time I check the codes, it comes up 34 (MAF).

It's a whole lot easier working on my 69 Pontiac!

 

If your problems always coincide with getting a 34, I would be directing my attention there. Have the FSM pages not helped with isolating your 34 problem ??

 

Get a fuel pressure gauge with a long hose and duct-tape the gauge itself to the windshield and drive around town for a while and watch it. Did you cut apart the fuel filter and see if there was any junk in it? Maybe the sock in the tank is plugged?

You might have a couple bad injectors, but it won't be all of them. I had 2 bad out of 8 on my 89 when I changed them at 83k miles and I was not having any driveability issues. This issue seems intermittent and they don't usually hiccup all at the same time, unless the pump is going bad.

53k is pretty low miles for an 89, sounds like the car has sat around so I would also make sure all the electrical connections to the sensors & injectors and tight and clean as well.

 

The car sat on and off for years down in Florida (right on the beach). It was my father's car. He's now in his seventies with poor health. He asked me if I wanted it a while back. I haven't had any electrical gremlins yet--just rusty bolts and such.

It had 44k on it when I got it at the end of last summer. I've done a bunch to it since -- mostly mechanicals. (Brakes, exhaust, u-joints, wheels, tires, shocks, bushings, radiator,headlight motors, belts, plugs, plug wires) I've been driving it quite often since and this problem started about two months ago.

After replacing MAF, Intake Air Sensor, Dist cap, rotor, spark control module, and fuel filter it ran perfectly for about two weeks. Then it acted up again on Friday. I bought a new fuel filter and then took the old one apart --- perfectly clean. I also cleaned every ground point I could find and unplugged and re-plugged every electrical connection in the engine bay. All connectors looked good and un-corroded. I re-torqued all intake bolts and throttle body bolts. I checked all vacuum hoses and such. Once I got her running, I took starter fliud and sprayed at all intake joints, vacuum connections to see if see RPMs increased---Nothing.

I will check fuel pressure today and clean throttle body.

FSM states:Code 34 Check intake system for air leaks and vacuum leaks, Clean throttle body, Check MAF connections, Replace MAF relays, Replace ECM*
Funny that it doesn't say replace MAF.

The only thing it could be after all this has got to be either injectors or fuel pump. Lastly I guess the ECM could be going bad. I feel like a goof just replacing parts.

 

Hi All--Thanks for all the input.

Here's where I am on this. Checked fuel pressure--turn key to auxillary and it imediately jumps to 42 and holds there. Fire it up and it falls back a little to about 38-39. It does jump around a little when I hit the throttle. Bounces around in a range between 38 and 45.

Cleaned throttle body and IAC. IAC had build-up around the end of the pintle. Put it all back together and it still doesn't want to start and run right. Then I shut it down and began putting tools away. Got back in it about 15 min later and it fired right up like brand new. Great throttle response and all.

I checked for codes and got (34) again. Does anybody know if bad injectors will trip code 34? Unless somebody has a better idea--I guess I'm down to replacing injectors, replacing ECM or MAF.

Thanks for any input.

 

the injectors are garbage.
get an ohm meter if you want to be sure, but they have a limited life span, which is long gone.

 

My 89 coupe had a similar problem and it was the ECM. My coupe did not have any codes though.

I would change the fuel injectors though since the Multecs will fail or are failing now. I installed the FIC injectors and very happy.

Kevin

 

http://members.shaw.ca/corvette86/Code%2034.pdf
What FSM do you have ??
I see no where that you have replaced the MAF power relay. Have you replaced it ??
Do you get a code 33 with motor running and MAF disconnected ??

 

Did you ohm the injectors yet? You should do this next before buying anything, maybe you can rule them out. As Agent86 stated above, do it both cold and hot. Cold first and if they are Ok then do it hot. On my 89 when I did it cold I had one at 12.5 and one at 9 and the rest were between 16 & 17, so I changed them all. Just remove the electrical connector from the injector and measure across the tabs.

 

Ok. I ran the diagnostic Agent 86 sent to me. Came back with code 33 with MAF unplugged. Obviously you have a better manual than I do. Where can I get the one you have?

I ohmed the injectors and found the following:
Cold: every one had 16.3 I thought this was weird so I checked them all again. Same 16.3 for every one.
Hot: 5 of them at 17.3, 1 at 17.4, 1 at 17.3, 1 at 17.2, 1 at 17.1

I bought and installed new MAF today. Before I fired her off I re-calibrated the IAC and TPS. Both were out of tolerance. When I fired her up she ran rough for about 30 seconds then settled down and ran fairly smooth. I guess the ECM was "re-learning" the settings. Still has strong rich smell to exhaust.

I let her heat up and took her out for a hard blast run on a road I can really push in the turns and down the straights. Glad I put big brakes on! Ran great. I even stopped and smoked the tires from a dead stop. (No power brake)

I went ahead and ordered the Bosch IIIs from Jon at FIC. He seems to think the spray pattern may be bad and is allowing raw gas to reach the O2 sensor which is fooling the ECM into thinking the MAF is not functioning properly.

I'll report back after the injector install.

 

What does the O² sensor look like? Is it really sooty?
Have you read the plugs? How do they look?

 

Installed new injectors from FIC. Delivered within 48 hrs. Gotta love that. Took a little longer to do the job than expected with rusty 20 year old bolts. Also, had a friend powder coat the plenum and runners red while I had them off.

Looks like everything is good again. Drove around today ---maybe 20 miles. So far no leaks and no codes and runs good. Since the problems were intermittent, I guess only time will tell. It's raining here so I couldn't really run it hard to see WOT.

Now I guess I'll check into the supercharger for a llittle more power!

Big thanks to all who commented and provided info.

 

It's back---only a little different. SES light came on today after about 15 miles of regular driving. Didn't run it hard or anything. Just cruising around. I'm really chapped off after fooling with this thing for a month! I would rather pull the motor and build a new one than deal with this crapola.

Checked the codes and came up with 36 (MAF burn-off/power relay) I already replaced this a few weeks ago when this all started. I will get another one and install it.

Any other suggestions beside replacing the ECM? Does anybody have a really good electrical schematic for 1989 coupe?

I think it's time I went through this car's electrical system with a fine tooth comb. I already had to remove the PC board under the dash that controls the A/C. I found a loose resistor and had to re-solder it. That was last August.

Thanks to all

 

Just want to subscribe to this, interesting stuff.

 

Update---Replaced MAF burn-off relay and MAF Power relay. This time I bought them from Chevy parts store. Re-set ECM and re-calibrated AIC and TPS. It's been about a week and so far no codes. Exhaust still smells rich. Maybe because of the Cat delete.

So far I've replaced:MAF sensor, MAF burn-off relay, MAF power relay, Intake temp sensor, All new Bosch III injectors from FIC, Ignition module, Dist cap, rotor button

For good measure I will clean and re-gap plugs and replace O2 sensor this weekend.

Thanks to all.

 

You've really been the whole road, sorry but it is a great read and makes me wonder how to approach my own similar (not quite so bad) issues with my 92 C4. At 150k miles and as cheap as injectors are, I think they're worth doing with FIC, also the o2 sensors and some other basic and not expensive parts swapping, then see how she runs.

Thanks for sharing, keep us posted!