Hi everyone
I´m new in the forum, but i have been reading since i bought my ´93 6 speed a few months ago. I bought the car in the US and brought it to my country in South America. It was (is) in a really excellent condition with only 7.000 miles.
The only thing wrong with the car, was detonation (pinging) and a little hesitation under middle to hard acceleration. I use 95 premium unleaded.
Changed the spark plugs to one point cooler and the detonation disappeared, or at least i didn´t hear it anymore, but the hesitation remained.
I changed lot of parts (spark wires, coil, ignition module, tps, egr valve, etc. etc.), checked the injectors, for vacuum leaks, grounds and many other things, but the hesitation was getting worse and worse until the point that the car practically didn´t advance when i accelerate.
After reading in many forums i decided to check the knock sensors and its wiring; all was perfect: 4500 ohms and 5 volts at the end of the wire and at the back of the ECM, despite all that, i changed the sensors with no result.
During all this process, the car NEVER threw a code.
At one point i decided to leave the KS disconnected and for my surprise, the car began to run perfect: excellent acceleration, smooth idle, very good consumption, cold and warm start is excellent, the engine sounds like music….
Of course i have a code 43, SES light and fans on, so i took out the fuse and connected a switch to turn them on when needed (AC or high coolant temp).
The questions are:
Do i have an ECM problem or is there something else to check?
If the problem is in the ECM, could be the chip or some other module inside the computer?
As i told, the car is running very good, but, despite not hearing the pinging noise, can i have detonation?
Thanks in advance

 

Are you running gas or E85?

Get a scanning device that will work with your 93 and see what your O2 sensors are doing as well as knock counts. If it is runs well in open loop, that makes me think the computer is trying to adjust for something based on bad data when it goes into closed loop.

 

Thanks for your prompt answer
I´m running 95 gasoline (don´t know what is E85)
Both O2 sensors are new and are working fine
I´ll try knock counts. which count is normal?
With de KS conected, the only moment the engine works normal and fine is at idle, when i put first gear and try to advance the engine fails constantly in all gears and speeds.
At some moments it seems it want to work normally, but this ¨symptom¨ only last a fracction af a second.

 

Some good info in this link.... scroll to project 20 for knock sensors:

http://books.google.com/books?id=1Ti...ensors&f=false

 

Have you checked your fuel pressure at the rail?
Wonder if your fuel pump isnt weak.

 

Did you check the timing properly?

 

[QUOTE=383vett;1586320624]Did you check the timing properly?[/QUOTE

 

My mechanic check it with a scanner and told it was ok, but he doesn´t has experience with these kind of cars.
As optispark doesn´t allow to touch timming, can you tell me which are the correct grades of advance for this engine?
thks.

 

Count your blessings...and dammit, I want some of that 95 octane!

 

Isn't an Optispark pre set, so no timing? I know these years suffered from bad knock sensors, but only 7000 miles?

BTW, the OP is in Uruguay which is between Brazil (were they use E85) and Argentina.

 

I realy don´t know, but if optispark is pre set, the ECM varies the timing according to what the sensor "tells"? and if the sensor is working well, where is the problem?
I read the same from KS from these years, but i changed both and check the wiring and torque; all is ok now.
The car has actually 7450 miles but pre owner only drove 300 in 9 years!!!! so i´m begining to think the problem is in the computer as a consecuence of the disuse, maybe moisture or something.....but before trying a new ECM y must rule out other problems.
If i were sure that my car doesn´t detonate with the KS disconected, probably i just leave them that way.
You are right!!Ii live in Uruguay, a small country between Argentina and Brazil.
Here we have two gasolines, 97 (95 real) and 95 (91 real), both has between 3 and 5% of ethanol. Of course the second one is the most sold (93%).

 

I agree with cuisinartvette. Check the fuel pressure under load if you are able. Another thing to look at (8 actually) are fuel injectors. That's about 9 years on one tank of gas.

 

If it sat that long with gas in the system have you run a fuel system cleaner thru it? You may have already said but how many miles since purchase?

 

As the fuel was in really bad shape, i took it all from the tank, cleaned and tested each inyector, changed fuel filter and when i filled the tank, also ran a fuel system cleaner a couple of times
I drove 600 miles since purchase (november).

Perhaps i wasn´t clear enough, the car runs perfect with the knock sensors disconected, the trouble begins when i conect them, it seems my Corvette becomes a 1959 VW Beatle....

With the kind of gasoline i use, it´s very dificult to have detonation, but something is cheating de KS and the ECM is assuming there is a strong detonation and making trouble with the timing

 

His rating may not be the same as yours.
Many countries outside the the USA use a different (RON ) octane rating system
RON Research Octane Number.
MON Motor Octane Number.

AKI Anti-Knock Index.
This is the number that is posted on the gas station in the USA as "Octane". It is derived as (RON + MON)/2

so RON 95 octane = US 91 octane and RON 98 octane = US 93 octane.

 

I tryied whith racing fuel (103 real octane, imported and $20/gln.....) last weekend and with the KS disconected the symptoms were the same, so i can conclude the gas is not the problem.

The car runs son badly ALL THE TIME, that´s pure logic the fuel isn´t causing the ecm to delay timming an making the car practically a disaster.

I was surprised yesterday when i opended the ECM and saw that the chip was not the original, is an aftermarket one, hypertech or something like that.

Can this chip be bad enough to cause the problems or maybe the mess is directly inside the ECM?
I must be sure before trying a new ECM.

Where can i buy OE chips?

I also have the posibility to burn one.

thanks.