Ive just changed the 89 305 tpi to 350 tpi and I cant get rid of the spark knock. I used the same injectors and same computer. Heres what I have. 350 bored .030 flat top speed pro with 4 eyebrows,88-95 194 heads with 193 casting #,performer plus cam 204/214 duration at 0.050,Ive changed many sensors including the spark knock sensor.Ive set the timing at 0 with the spark advance wire unplugged.Im getting spark knock on any acceleration. Ive tried a little more in each direction and nothing works. Do I have to much compression ? I need some help and advice from anyone that really knows these TPI set ups. Thanks in advance. Dave

 

What did you use for the harmonic damper and front cover?

 

I used the smaller one like the one that was on the 305. The timing marks are lined up. Car runs and idles real good.

 

Check the grounds on the wiring harness that goes along the firewall behind the engine. There are two on one side that bolt to the head, and three on the other side that bolt to the other head. Sorry I dont remember which has two and which has three. But if those grounds are not connected to the heads, you will have problems like you describe.
The ground connectors are black wires that come out of the wiring loom and end in a ring connector.

 

Thanks Kevin,does it have to be grounded to the head? Ithink that I bolted them to the bellhousing bolts. Also could it be that simple and has anyone actually found that to be a problem 100% sure? Thanks and any response will be applied. Dave

 

As long as they're bolted to the engine somewhere, you're fine. Yes we have seen that to be a problem and grounding the wires solved it. That's why I mentioned it. Make sure they're all hooked up and you dont have a broken one.

 

Just out of curiosity, do you know if the 305 and the 350 TPI engines use the same knock sensor part number? If not, did you get a replacement 305 knock sensor, or one specifically for a 350?

I know in some cases that different engines require a different knock sensor because the frequency emitted when an engine spark knocks is sometimes different between different types of engine. If this is the case, then a 305 knock sensor might not pick up a 350 spark knock.

 

You said here that you used the same injectors and computer. This is probley where your problem is at. The injectors for a 350 are bigger, also the PROM inside the computer needs to be changed, the programming is different for the 350 because the 305 doesn't need as much fuel or timing as a 350.

 

I did ask for the 350 spark knock sensor,hopefully that is what I got. Also I didnt change the prom or injectors because of differnt opinions. Some say they are ok others say there are different.I wish that there was an absolute order of things that are a must,it would make things so much easier.Thanks for the ideas and suggestions. Dave

 

Prom and injectors are definitely different.

Car should probably run with the 305 stuff, but not overly well.

305 is 19lb injector, 350 is 22lb injectors.

My car started with the 305 prom, but I didnt try to do much other than that with it before swapping it out for a 350 prom, and my car runs 50x better after getting a custom chip burnt.

 

A stock chip controlling a high performance engine will not cause the type of problems he is having. A mismatched chip will cause the engine to run excessively lean or excessively rich at idle. The difference between a 305 program and the 350 program is much smaller than you think.

Everything I have seen shows the knock sensor to be the same for the different sized engines. The difference is the MAF cars and SD cars use a different knock sensor. However, other people have said there are different sensors for different sized engines. *shrug* I've been using the same SD knock sensor on 305's and 350's with no problems.

 

Kevin,there you go ,seems like everyone has a different idea.Im going to check the grounds like you suggested tomorrow.I remember the passenger side ones were very hard to get at.Id like to see an easy fix. Everything else about the motor is right on except for that spark knock. Thanks

 

I see. thank you clearing that up. but i have one quick question. If the engine was running lean wouldn't it cause a spark knock??

 

Where is the timing tab on the front cover? Directly above the damper at 12 o'clock, or off to the side?

 

It is the small damper with marks off to the side.

 

Not at idle. The computer doesnt check for knocking and pull timing until you get above the idle speed, which is 14 mph.