I am new to forum, but not new to corvettes.

I have a 1987 4+3 coupe that has always had a knocking problem. Here is list of what has been done in the 2 years I have owned the car: new plugs (twice!), new wires, timing set three times (wire was off, different shops), new distributer cap, cat convertors all bad this helped performance alot, but still knocks, k&n air filter.

Any ideas?

thanks! :seeya

 

What is the base timing set to right now? What octane gas do you normally use?

 

Timing set to stock settings for an 1987. I do not remember what the mechanics said it was, but they all said it was correct. I always use 91 octane.

I forgot, I also had the injectors checked and cleaned.

The car will keep knocking once it starts until I let up on the gas, isn't the computer supposed to compensate.

This has been a problem for a long time and I appreciate your help.

Also the mileage is aroun 70,000. It just passed CA smog in December.

Thanks! :flag

 

Welcome!! :seeya

Higher octane doesn't help?

 

Have you ever tried replacing your knock sensor? If so make sure it is torqued correctly as over-torquing can make them over-sensitve.

 

How is the water temp? Have you checked the fuel pressure?

 

The parts person said that if it did not have a code than it does not need replacing. How do you check the sensor? Why no code?

The water temp is any where from 190 to 220 depending on traffic time of day. I did need a radiator and I had them put a 190 themostat in at the same time.

I do not know if the fuel pressure was ever checked. :seeya

 

Is it a pinging noise or a knocking noise. :confused:
I don't know if a 87 has a damper on the fuel return line.
Service Bulletin Number: 86234

Component: Fuel: Fuel Injection: Unknown type: Accumulator

Summary: Fuel return pipe rattle/knock-hammering/knocking type noise -- Caused by pressure pulsatings in fuel system generated by fuel injector operation. -- Repaired by installation of a filter/accumulator assembly in fuel return system. -- Service kits containing parts available from GMSPO - Service Kit P/N - Coupe 10068791 - Convertible 10068797 - All 1985-86 Chevrolet Corvette models.

I heard of people that had this problem on the 87 also.

Just my $.02 :thumbs:


[Modified by sumoboy, 1:48 AM 3/30/2003]

 

Pinging like if you had bad gas.

I also replaced the fuel filter but forgot to list it.

:seeya

 

Scorp508

Thanks for all your help, but I was wondering what the Scorp508 means.

I also noticed that most forum members have a 100% rating but yours is 77%. Does this mean that you are a bad boy? :reddevil


[Modified by imavettegirl, 5:54 PM 3/29/2003]

 

It does. :yesnod:

Scorp508 stands for "Scorpion" which is a name I used to use and 508 which is my area code in MA.

 

Anyone think computer might be an issue?
I would think between the Knock sensor and computer would be the bad link.

Thoughts?

Matt

 

Give this a shot, it works for my SUV.

Find a nice stretch of highway, preferably going uphill. Accelerate from 60 to 90. Then back off and do it again. Repeat this three to four times.

What you'll be doing, is "blowing out the carbon." By loading down the engine, you're super heating the combustion chambers, and you're eliminating any carbon buildup from chambers. Driving a lot of short trips can cause this carbon to build up, among other things.

If the buildup is bad enough, the octane level will be nearly irrelevant. The carbon buildup heats up and acts like a glow plug, thereby preigniting the intake charge.

Good luck with it. I hope this helps. Also, even though you run the better fuel in the car (which comes with nice additives and cleaners), it wouldn't hurt to dump some fuel treatment in the tank.

:cheers:

 

What about the coil itself :confused:
Sounds frustrating :cuss

 

Out of curiosity, how do you know for sure that the knock sensor is seeing anything? Also, unless the knock condition is severe (i.e. engine on the verge of blowing up), it is very difficult to hear. I'm wondering if you're maybe hearing something else.

 

You might want to have the plugs checked...

I ran the Bosch platinum plugs in my 88 TPI IROC Camaro and had some drivability problems... The dealership swapped out the Bosch plugs for some Delco plugs and the problem went away...

Most of my driving in the IROC was very easy going driving and not enough frequent high RPM time... Basically I was babying it and not driving it hard enough to keep the plugs clean... They would load up with carbon and cause some pinging which I mostly attributed to bad gas... The car ran much better after they removed the performance plugs and put the OEMs back in...

The Bosch plugs themselves weren't the problem, many people use them with no bad effects... In my case though they just weren't compatible with my driving style...

If you're not getting a lot of good freeway time (not stop and go traffic) you might be loading up on carbon... I saw that someone already suggested that you run it hard a few times to see if that helps...

Also if you've never changed the O2 sensor, I'd suggest that also... They're cheap on the older cars ($25 for Bosch replacement at Kragen, Autozone, etc)... Maybe the sensor isn't giving a true reading and is running the engine lean... I've seen older sensor replacement suggested each 25K miles for older non-heated types...

Hope this help...

 

That helped another car of mine w/ TPI... 02 sensor was trash but did not set a code for a long time... Once it did - that made it a no brainer to swap :)

 

There is also an ESC module (Electronic Spark Control) which is a 4-wire squarish module located on the pass side of eng comp near the fenderwell/AC unit. (This one is *not* in the distributor).

These have changed over the years, there are about 4 different part #'s depending on your year. Some members of this Forum (including me) have had luck with knock by upgrading to latest module.

I've had a bad wire going to my knock sensor and it did not set any code nor prompt any trouble indicator light. I suppose it depends on wheth it is broken or grounded, but you have to remove a small tin plate to check it.

...And Scorp *delights* in pissing people/moderators off, hence his Low % rating...And High entertainment rating... :D


[Modified by Rich B., 10:16 AM 3/30/2003]

 

If you hear the ping, the piston is moving up and the explosion is trying to force it back down. Not good. I have experience replacing pistons caused by this problem.

As a review, when the ESC system senses a knock (through the sensor), the timing is retarded 4 degrees, system evaluates, four more degrees, evaluate, 4 more degrees, down to about 16-20 degrees max retard, depending on model, etc. If you hear a knock, the system has failed to detect the knock, or the timing is backed down to the max, around 20 degrees, and the retard is not sufficient to quell the knock. Another really bad thing, damaging shockwaves may not be heard, they can exist below threshold hearing.

Find someone really knowledgeable about this system, with a good scanner, and see how many knock counts the system is seeing and any retarded timing values.

For the interim, if you hear that sound, I'd lay off the throttle.

Good luck, let us know.

dlmeyers 90 coupe zf6 3 speed shocks

 

Just wanted to welcome you to the Forum. :seeya