Car starts easy and runs perfect when cold. After it warms up (gets hot) I get some timing ping even with hi-test and octane booster. Worse than the ping under load is the clattering noise at WOT.

I have a 160 degree thermostat. I don't think it's the original motor either. Would 6 degrees BTC be correct for newer (86-89) engines too?

Any suggestions from the Corvette forum brain trust? I've already tried GM top engine cleaner. Can't find any vacuum leaks. I need more things I can try. I've tried Octane booster and I've tried disconnecting the wire (br/tan) that you unhook to set the timing (it ran worse).

Could it be:

a) Base timing incorrect
b) ECM prom needs reprogramming
c) Carbon build up
d) all of the above
e) none of the above

Please help!

 

Also consider EGR system failure or lean mixture.

 

See if you can't find one of the forum members in your area with a scanner...I'm into my scanner with Moates cables, FREE Tunerpro RT software and used laptop for about $200.

6* is stock timing, I'm running 8* base timing.
Can you find out whether the engine is stock or not? Your computer won't need programming if it's stock!

May need a good tune up.

 

What's the difference between pre-detonation and detonation?

 

Pre-detonation fires before its supposed to

 

What Rick L said. You can do a lot of guessing plus throw bunches of money at it but a decent scan will point to your major issue.

 

I've done a scan (DIACOM) and put the information out here and still got a bunch of guessing. I need a sequence of tests I can do to pinpoint the problem. Of course then I was looking for a different problem (electrical). I'll repost the results of my previous scan and maybe get some insight.

Engine Speed................... 700 RPM
Vehicle Speed.................. 0 MPH
Coolant Temperature............ 176 F
Manifold Air Temperature....... 104 F
Throttle Sensor Voltage........ 0.42 VDC
Oxygen Sensor Voltage.......... 668 mV
Oxygen Sensor Transitions...... 151 #
Idle Air Position.............. 32 #
Air Flow Rate.................. 5 GPS
Injector Pulse Width........... 1.6 mS
Spark Advance.................. 0.0 DEG
EGR Duty Cycle................. 0 %
Integrator..................... 125 #
Block Learn Multiplier......... 160 #
Spark Control Counts........... 0 #
Closed Loop Status............. On
Fuel Mixture Status............ Lean
Battery Status................. Norm
Torque Converter Clutch........ Off
Park/Neutral Switch............ On
3rd Gear Switch................ Off
4th Gear Switch................ On
Power Steering Switch.......... Off
Learn Control.................. On
A/C Request.................... No

------------------------------------------------
TROUBLE CODE STATUS
------------------------------------------------
No current trouble codes present

Thanks!

 

If you have the Factory Service Manual there is a chart with exactly the kind of step by step diagnostic procedure you are seeking for your no fault code symptom. (detonation and spark knock)
Should be section 6E3-B

 

Your knock sensor may have failed.

 

While this only shows idle, I would be wondering why it is so lean (160 BLM is way lean)

 

Fail safe logic in the ECM retards timing when the sensor fails.

 

I also wondered about the lean condition. Check your injectors to see what the resistance is. If one (or more) are failing, you can get a lean miss. Mine also did it when hot -- but not noticably when cold. It took quite awhile before the injector showed bad when cold. You might even have more than one that are failing.

They should read 16 ohms or thereabouts. Measure ohms across the contacts of the injector plug-ins.

Gregg

 

no such thing as "pre detonation"....
only detonation, and pre-ignition. and yes, they are quite different...
if its audiable, its detonation. pre-ignition is silent, but much more destructive.
verify your ign. timing setting with the proper procedure, and adjust if needed. the above mentioned lean condition is also a possible cause.

 

That is not a true statement. The ECM operates by advancing the timing to a known setting that will cause pinging the first time the engine temperature exceeds 195 degrees and it is at WOT. If the knock sensor detects knock the system is operating correctly, if no knock is detected it will set a code. Since he has a 160 degree thermostat the engine may never get over 195 degrees and it may never run the knock sensor check.

The timing is only retarded once the code is set after the knock test is preformed.

 

I got my information from page 87 of George Probst's book Corvette Fuel Injection, if it was incorrect I apologize. He does not explain the parameters used to determine when the sensor has failed.

 

check your tps voltage. stock 85 should be .54 yours is only .42

matt

 

TPS voltage has been reset to .54. That was the one thing I could correct with the DIACOM program.

How exactly does one check injector voltage? Can you be more specific as I am car electric challenged. This has been suggested before but I was too busy (driving it) this summer to work on it and forgot.

Can anybody publish or link to the FSM section 6E3-B please for procedure for 'spark knock and detonation'.

My bad on the pre-detonation. I've always called it timing ping.

Thanks all

 

Okay, let's try a easier request...

Can someone tell me how to get the electrical connectors off the fuel injectors so I can check the resistence? I've tried squeezing them together to no avail and I don't want to break anything.

Thanks!

 

I'll take a stab at both questions. Notice the metal "spring" device near the bottom of the connector? It must be pressed toward the body of the connector to release, wiggle and pull on the connector (not the wires) at the same time you press the spring, they can be stubborn. No action is required when reinstalling, the spring will just snap into place.

To check the resistance of the injectors, set the DVOM to OHMS and select the lowest scale that will read up to 20 OHMS. You are checking the injector,not the wiring harness. Touch one lead of the DVOM to each connector on the injector (makes no difference which lead goes to which connector) and note the reading, should be close to 16 OHMS I think, your car could be different. Similar to a compression test you are looking for consistency between injectors, be suspicious of any that are different from the norm.

You can check power to the injectors by setting your DVOM to DC volts, connect the black lead to a good engine ground, turn the ignition key to the "ON" position, there should be battery voltage at one of the two wires to each injector.

The ECM "pulses" the other wire to ground to fire the injector, the easiest way to check that side is with a "noid" light, a test device available at most parts stores, it plugs into the electrical connector you removed for the resistance check, if it flashes while cranking the engine over the ECM has the ability to fire that injector, hope that helps.

 

I'm still trying to track down spark knock.

All injectors are getting power (12v) and read 16 ohms. I guess my next step is to check the EGR valve. Could someone please explain this process for me?

Is there any other way to find a vacuum leak desides spraying WD40 all over the visible vacuum line connections (already done)?