Morpheus53

I have a 85 with the l98 and doug nash 4+3 tranny. This has been beaten to death on this site but I still can't figure out my problem. I am getting a code 43 only at 4800 to 5200 rpm after it has warmed up to above 195 deg. and the ECM runs its check for the knock sensor. I have replaced the knock sensor with an 87-89 less sensitive one. checked all my wiring. Just did the Electronic Spark Control Module upgrade to PN# 160388331. It seemed to help a little. The only major upgrade I have is mid length headers with 2.5 exhaust no cat and magna flows. oh and I put an AFP regulator and am running 38 psi at idle. I also run 91 octane with octane booster. I also recently adjusted my lifters to spec. they were all about 3/4 turn to a full turn loose.
I can't really tell if it might actually be knocking at wot because it is super fast and loud. ???????????
Any ideas would help? replace ECM?

bjankuski

Have you looked at the knock control module mounted on the outside of the blower motor housing? The design of the system for checking for knock is crude at best. As you stated if no knock is detected by the ecm during the entire time it is running, it will perform a knock test the first time you go to wot once the engine exceeds 195 degrees. The test advances the timing to a point that it assumes will cause knock and if no knock is detected it assumes a component has failed and sets the code for knock system failure. So the code will be set even if the system is operating correctly and their was no knock (maybe your base timing is low and no knock actually happened), or if knock happened but was not detected. Either way I do not like this test because it is promoting engine damage by trying to cause knock at wot above 195 degrees. On a stock engine maybe it is ok but on a high compression high output engine it can cause issues when this test is run.

DanielRicany

Try running your tank low and using half a tank of 87 octane with no booster.

Morpheus53

I replaced the knock control module or ignition module or electronic spark control module with the updated part number 160388331 as adviced on this site. It is supposed to be the best upgrade. took me four months to find one. helped a little. raised the code coming on from 4600 rpm to 5000 or 5200.

Morpheus53

I can try that. What is your theory behind this if I may ask?

bjankuski

Where was this part located? In the distributer or on the outside of the heater box near the fender?

DanielRicany

This fixed my problem. I was using high octane gas and the ECM could not get the engine to produce a knock signal to verify the knock sensor test. Since no signal was produced, it set a check engine light. As long as I used lower octane gas, it never came back on. I changed my set up and disabled the knock sensor diagnostic in my tune so I could run high octane gas and not worry about the check engine light coming back on.

Morpheus53

On the fender with a five terminal plug. goes to the knock senor and determines when to retard the timing due to knock and also talks to the ECM to tell it set code. Two screws hold it on 9/32 size bolt head.

Morpheus53

LOL that sounds like what some stupid idiot in 85 would do to a car. I guess that would make a lot of sense. In this case then I want to run high octane gas so what tune do you have and I'm a great hard core mechanic but when it comes to tuning and programing i'm lost. Do I need to start with a PROM or do I need a special tuner or cord to hook up to my laptop with special program? I understand the communication part of everything but what do I need to get tuning? I really love this car and got it cheap cause it needed work. been fighting this code for 4 yrs since purchase. Runs great when cold but that code haunts me. I'm a married man with two kids as a mechanic so i'm nickel and dimeing this car and have a 20 yr plan. this is the last mechanical flaw I have before dyno test. Then on to all the cometics. Any help would be great.

DanielRicany

A stock '85 has a recommended octane rating of 87. So you are wasting money dumping high octane in it trying to prevent detonation from a low compression engine with 32 degrees of total timing stock. I use 93 on mine because it not stock at all. However, if you did want to turn off the knock diagnostics you would have to send your ECM out to have an adapter soldered in and then have someone burn you a tune. Probably would cost you somewhere around $100 total for just that. I seriously recommend trying the lower octane fuel before tuning the code out.

Morpheus53

So where do I send my ECM. I will soon be needing high octane with planned mods. I will run lower octane until then but this car will be way faster when i'm done.

DanielRicany

You need to contact moates.net.

They have an adapter that you have to purchase and they will solder it in for $25. I don't remember the name of the adapter.

You also need to purchase the chips from them and the Burn 2 burner.

You'll need an ALDL cable that connects to USB from aldlcables.com.

You also need tuning software such as Tuner Pro R/T.

Once you have all that you will be ready to tune.

The ECM that you have takes a little longer to tune than the later ones so be prepared to curse a few times during your tuning process.

I'd recommend having someone burn you a chip for basic things for now and then later when you start doing heads and cam then you can tune the rest by yourself.

Morpheus53

thanks I really appreciate the info. This car is surely very unique in everything they did to it.

bjankuski

Don't run low octane just to do it, first check to make sure your base timing is set at 6 degrees and then see what happens. My 1986 all stock vette with cast iron heads pinged with 87 octane fuel in it at WOT, the 1985 should be very similar. When I ran 93 octane fuel the pinging would stop but I could still see retard with my scanner.

Morpheus53

It is currently running at 8 degrees. I checked it first with the code 43. I read that 8 was optimal but who knows the most about these cars. factory was 6. I can set it but its not pinging at all right now and throwing that code still. I have a 185 thermostat and my main fan and auxiliary fans kick on at 205 so it takes my car 30 mins of driving to even get it up to 195 where it throws that code. I can run it as hard as I want all day until 195. then boom. and my car will only be over 195 for 1 to 5 minutes until my fans turn off at 185. cooler engine more power. the 2 degrees make that much difference? I love the way it runs just stupid code.

bjankuski

If it is not pinging and you do not want the code you could have it programmed out. Just a thought.

Morpheus53

I guess my next upgrade is sending my ecm out. I'll probably wait till winter comes and i'm not gonna drive it anymore and maybe run 87 octane and see if it has no code.

Morpheus53

lol now I gotta drain the fuel tank. ran 87 and got a good test drive on it. ran so so so bad. sputtering. the check engine light also came on at 1000 rpm on WOT. so I think it's sensing knock. think i'm just gonna run high octane and try to get my computer worked on this winter. think it's gonna need new cam because I had to tighten down my lifters quite a bit when I re adjusted them. that's why the knock is the at high rpm. just might try a new engine. cam and heads for the l98 are more expensive than a built engine.