MJ6

1989 convertible 6-speed: Problem, power loss with a slight miss, when I punch it through the gears I can smell a bit of gasoline. The car has run flawless for the last couple years, I drive it maybe once or twice a month at the most. This problem seems to have come with no warning, no trouble lights showing..Before I throw parts into it does anyone have some suggestions as to the problem. The slight miss is most notable when in 6th. gear at highway speed, throttle response is sluggish have to shift to 5th. on slight grades never had to do this before this problem arose. Also, most people wouldn't notice the miss unless they have driven the car before, it's that slight, but I can tell it's there as well as the loss of power an the smell of gas. Note, car has no cat. and exhaust is new with plenty of flow. I haven't had a chance to look into the problem yet and also wanted to get recommendations from the members. I did check for gas leaks,(none) and all the plug wires seem OK..Thank you and hope to hear your thoughts.

MJ6

88 Views and not one reply. Someone has to have an idea or two before I start replacing parts. Would appreciate it.

ctmccloskey

Hello MJ6!

First, How old is the Oxygen sensor?
The reason I ask about your O2 sensor is that we have found a lot of people using these devices for much longer than they were designed for. On OBD1 cars you replace the O2 sensor every 50,000 miles or 24 Months. This is why I ask how old it is. IF your O2 is out of this schedule then you should replace it anyway. The Oxygen sensor is a very important sensor that "wears out" and needs to be replaced every so many years. The O2 will affect your performance and economy negatively if it is old. The O2 sensor sends a signal that oscillates between .1 and .9 volts very quickly. As they age the signal starts to lag behind and the signal strength gets narrower and it will have a profound effect on your engine.

Have you done anything to the MAF sensor?
I have a Buick DD and it started missing and acting funny when loaded up with a trailer on a hill. It would just act like it was missing and surging a bit. I hooked up my trusty scanner and found I had a bad MAP sensor. On my 1988 C4 I have a MAF sensor, the newer cars switched to a MAP sensor but both serve the engine by measuring the volume of air being ingested into the combustion process. On a car with a MAF we have two relays, one turns it on and the other activates the Burn-Off relay. The burn-off relay will send power to the MAF sensor and make the little tiny 1/10mm wire glow red and burn off any contaminants. This system is great while it works but sometimes it fails to clean the wire and then problems might start. You can purchase a can of spray MAF cleaner at a auto parts store and try cleaning it to be sure that is not your problem. Frequently when the Burn-off relay system fails the ECM will set a trouble code. If you ever replace a MAF sensor be sure to replace both relays at the same time.

As for the "slight miss" I would try some B&G 44K Fuel Injection cleaner as it is one of the best for cleaning up the injectors. Some call it "Snake Oil" and won't even try it, it is all up to you. I love the stuff and I also know that a lot of car dealerships use it to help their customers. On my 1988 the idle would start to miss a bit and after a can of B&G 44K in a tankful of gas the problem would go away. You can buy it on Amazon easily. I only recommend products I have lots of experience with. If you replace the O2 with a new one it might help with the misses and power issues.

Best regards and Merry Christmas!
Chris

C5 Diag

Unfortunately without some diagnostic equipment you are going to be "guessing" anyway !!!...we can offer 10 suggestions and any of them can be right...there is no silver bullet !!

MJ6

ctmccloskey: Thank you for your reply it was appreciated. You had some excellent ideas, however, once I was able to make time to check things out I discovered a mouse had chewed a plug wire connecting to the distributor. I was unable to see it without taking the disb. guard off, also the critter had began chewing another wire beside the first. I replaced the two wires and everything is in tip top shape and running excellent, I won't replace the wires with new until my garage is mouse and or rat free.. I also have to locate a bad electrical wire in the ceiling of my garage that I bet has been chewed by these pests. I have to remove insulated panels to reach the wires, believe me this will not be fun, however I'm without lights so, it must be taking care of. Thank you again for you reply.

MJ6

Thank you for your reply I located the problem, mice had chewed a couple plug wires near the distributor. See post I wrote to Senior member ctmcloskey.. Thanks for your reply I appreciate it..

GaryInArizona

Hey Chris I was wondering if you might be able to help me figure this out. I have a 93 LT1 and it's running rough. I have code H64. I pulled out 02 Sensors and tested them with propane heat and they tested good. I can't get rid of code and car is still running rough. Any ideas? Appreciate it. Thanks.
Gary

ctmccloskey

Hello GaryInArizona!

You mentioned that you tested the oxygen sensors with "Propane Heat and they tested good". Can you please tell me how you did this? I have heard of putting propane into the intake air and watching the O2 sensor react but never using heat from propane.

The oxygen sensor is a device that wears out way too often and is often overlooked on the older C4 Corvettes. Fortunately my 1988 only has one. I am not sure how many came on your Corvette but if and when you replace them do them in pairs on each side. I prefer to replace all at one time but that gets costly when you have four of them like the OBD2 cars came with.

On the OBD1 Corvettes the O2 sensors were designed to be replaced at 50,000 miles or 24 months. OBD2 cars can go to 100,000 miles and five years. As O2's age they have a really bad habit of lagging behind and the the signal starts to narrow. The performance and the mileage would suffer until they fail completely. A lot of gasoline is wasted because of old oxygen sensors...

How many miles are on this Corvette of yours? Do you have an operating emissions system? Does your car have a PCV on it? Are all the hoses secure and no vacuum leaks? A vacuum leak can set a lean condition I believe (I might be wrong) as it does on the older C4's with the L98. Cars with PCV valves can sometimes leak enough air to trigger the right side lean condition.

The fact that your car is indicating a right lean condition from the code H64 it makes me wonder what is coming out of the O2 sensor. The big question why does the ECM see the Lean condition on the right side? Do you have access to a OBD1 scanner to watch your engine information while it is running? The Oxygen sensor is supposed to oscillate between .1 and .9 volts very (very) quickly and it is hard to see without the proper equipment.

I do have a testing rig I bought from Mid-America that plugs into the O2 and the O2 harness plugs into the test rig. It uses a decent meter to watch and verify operation of the O2. If you don't have access to a Scanner maybe you can make one of these jigs easily enough.

There is a book written about the C4 fuel injection systems and I am going to read up on a couple things. If the you get a chance send me the answers and we will get this figured out for you.

Best regards,
Chris

P.S. Are you using the stock injectors that came with your Corvette? If they were replaced how long ago was it?

GaryInArizona

Hi Chris. I removed 02 sensors in front of CATS and put them on vise. I took black wire from multi meter to ground on 02 sensor, I took red wire to power source on connector on 02 sensor. I took propane torch heated up end of sensor and meter went from .0 to .9 just under 1 volt very quickly. Took heat off of sensor and it dropped down very quickly to .1, According to this test the sensors are ok. Or so I have been told. I replaced fuel injectors. They don't have 15 minutes run time. They all are firing as they should. I checked voltage to injectors. All the same. Still showing code H64. My car has two 02 sensors. Car has 87K miles. It does have operating emissions system. It does have PCV. I checked all the hoses to make sure they were secure and no vacuum leaks. I checked all cylinders. They all have good spark. I checked fuel pressure at fuel rail and it's normal. I just replaced fuel filter. I do not have OBD1. I don't even know what that is??
I just replaced fuel injectors with stock ones. I cleaned fuel system and drained the fuel tank. I just can't figure this out. Driving me crazy! Any ideas will greatly be appreciated. I will be replacing 02 sensors Monday. Thanks for your help.
Gary
Gary

GaryInArizona

I all so removed one at a time power connectors to fuel injectors and # 1 # 3 made no difference at idle to the way it runs??

MJ6

Did you check to make sure you have power to #1 and #3 injectors with a multi meter or similar device? If you do, either the injectors are not pulsing or their bad.. What happens if you pull the plug wire to these cylinders, does that change anything? Also, pull the spark plugs out to 1 and 3 and see if they are wet with gas.. If none of the above changes the way it's running it could be your computer.. Get yourself an OB-1 scanning tool, you can buy one at walmart or any good auto parts store, remember the OB 1 scanning port has 12 pins the OB 2 scanner has 16, and will not work on your car. I paid $30.00 for mine bought it through walmart...The way you explained the problem it seems like you have 2 dead cylinders and I doubt it's mechanical more likely electrical.. Oh, when you pull the plugs wires do it one at a time and give it 10 to 15 seconds and listen..
Let me know how you make out..

GaryInArizona

Yes did all those tests after running car for a short time # 1 exhaust is not getting near as hot as the rest of them ? So no fire on # 1. I had to order OBD1 sensor and it should be here by Friday. I will let you know after I get it. Thanks.
Gary

MJ6

Yes let me know how you make out.. If compression is good in #1 it has to be electrical one would think, unless that fuel injector is not functioning correctly as you have some heat in that cylinder..

GaryInArizona

I got OBD1 scanner today. Plugged it in and the only code that comes up is 12. Now what? I checked compression in #1 cylinder and it was 175 lbs. Pulled #1 spark plug and it has great spark on #1. And I know the fuel injector is firing as it should. Now what? Any more ideas? ECM??? I don't know how to check that.
Thanks.

GaryInArizona

Also when I plug in scanner and turn ignition on the air pump starts running and continues to run. And I noticed that #1 spark plug has a little bit of raw fuel.

GaryInArizona

I took car out and made a couple wide open runs. Car seemed to pull pretty good. When I got back the car was still idling very rough. So I re-installed scanner and it showed 21 code. Which says Throttle position sensor (TPS) Signal voltage is high. Then I unplugged Throttle position sensor and started the engine and it that made it run worse. So I plugged it back in while the car was running and it smoothed it out a little bit. I put scanner back on and it pulled 22 code.
Which says throttle position sensor (TPS) Signal voltage is low. What the heck? Could that be a problem with ECM? Or should I just replace Throttle position sensor? What are your thoughts? Appreciate your help. Thanks.

MJ6

That scanner has me concerned, the air pump coming on don't sound right.. Personally I think it is the ECM.. Did you check the voltage amount going to the TPS? If it's showing different amounts than the normal range which is 5 volts, there is a way to test the it w/ a volt meter.. Touch the negative probe on the volt meter to the negative wire tab on the TPS and the positive probe to the positive tab. The volt meter will show around 5 volts if the TPS is working correctly. To check signal voltage. Touch the positive probe to the signal wire tab and touch the ground probe to the frame of the car..Also, they have cleaner which I'm sure you know about to clean the TPS. Also, after cleaning it re-test, if you are still getting erratic voltage then I would say the ECM is bad.The price isn't that bad for a new one, however, you can check your local salvage yard for known good one, although I doubt you would have any luck. I would Test, Clean, Re-Test before buying anything..Hope it helps, let me know how you make out..

GaryInArizona

Thanks for the info yes I did check the TPS working like it should I did find out I had a bad fuel cutoff relay circuit ? Replaced it and code 22 is gone. Now after we cleared codes it all looked good and I put paper clip back in and code H64 is back. Cannot figure this out. ECM? Is there a way to test ECM???? Do you know if I can take ECM in to be tested? All codes all clear with scanner. With paper clip in I still have H64. Also replaced MAP sensor. You are right about the smog pump blower turning on and now cooling fans are turning on too. What the heck is going on! This is driving me crazy. The smog pump blower and the cooling fans turn on when I plug in OBD1 scanner???

MJ6

ECM, inspect the PINs. You want to make sure there are all upright and intact. If that checks out, smell it, at the plug of the unit . If you get an odor of burnt plastic that lets you know that it’s bad.. If you want to inspect the board, open up the unit inspect for any burnt components.. Oh, does it still have a miss? Garry,this is about all I know you can
do to check the ECM yourself'..

Here is a reply from a guy with the H64 code: Do you have the FSM (Factory Service Manual)? The H64 isn't necessarily a TPS problem it just means that the TPS Module that the EBCM/ABS/ASR in the past hasn't seen the signal that it expects from the TPS Module. The TPS Module is mounted over near the evaporator/blower housing right side. Hood up I'd think right at the top of the fender panel or maybe just below.

You can check the SIR for flash codes BUT I don't believe you can clear them manually on a '92. Did you use the "flash codes" to diagnose the SIR code OR did you just rely on earlier information that mentions cleaning frame mounted sensors?

GaryInArizona

I finally cleared all codes. But the Evaporator blower and both cooling fans turn on when I plug in OBD1 scanner with key on and continue running. Why??
When I disconnect scanner they stop. And car is still running rough at idle. Where do I go from here? I can't figure this out. Again thanks for your help.