I just bought an 85...it will be my second project car...not anything real major. The problem that prompts my question(s)...the guy I bought it from, bought it with a blown engine. He is an accomplished, old school, shade tree mechanic... but unless the car has a points and distributor setup he is totally lost...fuel injection and all of the electronics are way over his head...that's why he gave up and sold the car to me. He put in a rebuilt non-corvette 350 engine...he put everything back together, but it would only start once in a while and would flood after a few moments.

When I bought it I had to have it towed home. While my bother and and I were looking it over, we found what appeared to be the knock sensor wire/connector dangling and melted. We could not find a knock sensor in the block...I understand it is in the vicinity of the starter...(I'm waiting on a 85 service manual to come in to confirm this). We found a drain plug were we thought the sensor was supposed to go, but no sensor. My brother knows more than I do about engines and he said he didn't think that a sensor could be put in this block in the drain hole.

I don't have the block casting numbers so I don't what year it is or what it came out of...time permitting I'll be looking for the numbers later.

1) can a knock sensor be installed in place of a drain plug (my brother thought that water turbulance in the water jacket would give off false readings to the sensor)?
2) if not where could a knock sensor be place in a non-corvette engine block?
3) this can't be the first time this has ever happen...anyone aware of any work arounds?

The previous owner put a in a new fuel pump and regulator, trying to resolve the flooding problem. I posted a question eariler...before I bought the car and several people suggested changing the coolant temp sensor...that will happen shortly.

Any ideas about the knock sensor?

 

I'm not exactly up to speed on the electrical side of things either, but I would bring #1 cylinder up to top-dead-center. Take off the distributor cap and make sure the rotor is pointing to the #1 terminal.
It gives you somewhere to start. Good luck.

 

Yes, pull a knock sensor on a any C4 and you'll get wet.

 

Yep, that's where they go! Commonly pulled to drain the coolant.

 

Thanks for the quick responses...I'll be picking up a knock sensor and getting it installed, along with the coolant temp sensor. Now I just have to find a connector to replace the burned/melted one.

 

There is no "Corvette" block. The knock sensor is installed in the right side block water drain plug hole. I would wait and test that water temp sensor to be sure it is defective before you start throwing money at the problems, needlessly. One can waste a ton of money guessing at the causes of problems.

RACE ON!!!

 

the knock sensor is a pipe thread just like the block plugs are , and on most gm small blocks they thread into the water jacket, be careful not to overtighten these also they can be damaged by overtightening. If it helps any the knock sensor only retards timing when it "sees" detonation, the ecm advances timing until it senses a knock and then it retards from there. so although the knock sensor needs to be connected it usually only throws an ses and can cause spark knock on acceleration.

 

The knock sensor does NOT" only throws an ses" and it can NOT "cause spark knock on acceleration". Bad information and for no reason.

RACE ON!!!

 

 

if the knock sensor was removed I would also be looking to see what else was removed/unplgged etc. which might reveal other problem/s.
no, timing is setup as a defined table in the prom/chip; timing vs. rpm vs. load/kpa, and the ECM does not keep advancing the timing.

 

You can pickup the connector at the dealership. I believe the part number is 12102621.

 

What?

 

since he was having other drivability issues I was attempting to rule out the knock sensor as the source of his flooding problem, quite poorly I must admit,sorry.
But in my last 20 years as a GM dealership tech I have never had a Knock sensor cause a flooding problem, I have however had alot of Service engine soon lights on due to grounded or open sensor wires, also the ESC system has trouble finding maxumum advance and I have had severe detonation symptoms on the older cars before the ECM sets a code.
So although the Knock sensor should be fixed, my intension was to suggest that fixing the knock sensor most likely wont have any real impact on the running condition of this car... Guess I should quit posting at work when theres too much going on.

 

CFI-EFI seems to be an intelligent guy, but I just dont see any point in getting brutal with people. Were just trying to get some tips, not get spanked.

 

I don't think the knock sensor has to do anything with the flooding either...I'm looking at the knock sensor as a possible cause (because the sensor is missing) as a possible for the intermittant starting.

You guys have been helpful...I'm going to tackle it (trying to get the engine started and stop the flooding), this weekend...hopefully I'll have good news to report.

 

One thing you might check, the egr valve is often the reason alot of "flooding " diagnosis is wrong, if the vacuum lines to the egr are incorrect or the solenoid is bad or improperly installed when the engine develops vacuum the valve opens when its not supposed to, dropping intake vacuum, causing the map to see high engine load and in turn the ecm dumps alot of fuel to compensate, also coolant temp sensor can do similar things, running the injectors full rich to compensate for -34 degrees if the sensor is open.
The egr would cause extreme rough running, smoking, rich smell, possibly hard brake pedal, coolant temp sensor would cause more fuel smell, loading up, general poor performance.
Also since the engine has been changed look for the ecm grounds on the engine, often are damaged of not hooked up at all causing the ecm readings to be all wrong and totally useless.

 

You never addressed the drivability or flooding problems. You only made statements as the the ESC function, several of them totally incorrect.



There is no possible way a knock sensor COULD cause flooding. So even the statement, "I have never had a Knock sensor cause a flooding problem" is pointless. That is like saying you've never seen low tire pressure cause flooding. Duh!



The ESC system doesn't search for maximum advance in it's function to sense knock and retard the timing to alleviate it.



Too bad you made no mention of "the running condition of this car"

RACE ON!!!

 

Tips are good. False tips like, "...so although the knock sensor needs to be connected it usually only throws an ses and can cause spark knock on acceleration." are misleading bad information that can possibly cost the otherwise uninformed time and money. It wasn't my intention to be brutal. Of course you knew better all along, so how would YOU have worded it without giving a spanking? And why didn't you?

RACE ON!!!

 

Not only does the lack of a knock sensor not have anything to do with flooding, it also has nothing to do with hard or intermittent starting.

The ECT (engine coolant temp) sensor, if disconnected or dead could cause the ECM to think the engine is at -40° F. Not only does that cause the ECM to command an extremely rich (choke on) A/F mixture, it also commands a fast, cold idle speed, like a choke would. Is your engine idling at 1500-1800 rpm or so? The ECT sensor can be tested. Even though the ECT isn't particularly expensive, throwing money (parts) at a problem is a poor way to diagnose(?).

RACE ON!!!

 

Speaking of spankings, How do I get Into the 13sec. Club? Pull a couple spark Plug Wires off???