Knock sensor

Good afternoon,

Which timing marks? The one with the chain or the distributor?

No, the knock sensor will not effect the timing at all. The PCM will change the timing internally when it detects pinging. If you have a scan tool, you can monitor the knock sensor pids.

Roy

Well the only reason that I suspect the knock sensor is because nothing else makes any sense as to why the timing marks will not line up. It's on the #1 TDC and the rotor is pointing to the right mark on the distributor. Compression is good, fuel pressure is good and I have spark on all plugs. What else could it be?

Okay,

What is the exact fuel pressure?

A clogged catalytic converter will cause this as well.

Roy

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

I do no know what the fuel pressure is because I had put it into a shop and told them to see if they could figure it out. At $115.00 an hour, I could only afford a couple of hours and they gave me another half an hour for free and said that I have spark, fuel, and compression. And said that it is sounding like something mechanical. They said to check the valves which I pulled the valve cover and seen that everything seem to be working like it should. They also said that it could be the cam lobe on the #6 being wore out because that is the cylinder where the misfire is. I get two codes from the scanner, P0300 and a P0306. How does the catalytic converter mess up my timing? And there is a rattle in the cat area which I knew of but I did not think that would cause the timing to mess up.

300 is common for low fuel pressure.

timing is controlled by the chain and the distributor. did they check that?? did they check to see if it jumped time??

the rattle in the cat could be it is broken inside and clogging up the exhaust. if it is blocking off the exhaust, it will not let the engine breather and it will not start.

Roy

I put the chain and gears on and made sure the dots were lined up.

When you removed the valve covers, were all the valves moving the same distance?

I would also back up and recheck the fuel pressure as well. Low fuel pressure will do this as well.

Roy

I will, but would low fuel pressure cause just the #6 to misfire? If so, how?

Yes it will. Not enough fuel to fire the cylinder correctly.

Roy

I got under the truck today and the catalytic converter is rattling pretty bad. So when I get enough money up to get another one, I will change it out. I do not have a fuel pressure gauge but maybe I can rent one and see what it is. If is where the book says it should be, what then? And what can altar my timing mark by at least 10 degrees. Is that something that is needing a computer to readjust?

Where are you seeing the timing change?

Yes, you can rent one at a parts store.

Roy

The harmonic balancer mark is not inline with the ear mark on the timing cover. Looks like it is 10 degrees out. But no problem with starting up or turning off.

If you line it up with TDC on the pointer, where is the rotor pointing?

I have two marks on the distributor, one says 6 and the other 8. I have a 4.3 so it is the 6. I also have two timing marks on the balancer, the book says to use the one on the left standing in-front of the truck as the timing mark.

Okay, did you pull the number one plug and verify it is at top dead center and the line on the pointer is correct?

Roy

Yes, several times.

Do you have a scan tool that can read the cam retard reading for the distributor or the cam sensor? It should be close to 0.

Roy

I will look at it tomorrow but I do remember seeing it before and it said 21 degrees.

This is the biggest problem I have that it is out that far from 0. Do you know if this system requires a scan tool of some kind to set the timing.

The scan tool lets you see the timing. You adjust the timing by rotating the distributor to get it as close to 0 as you can.

Roy

This is the problem with this situation, this year truck 1998 4.3 GMC Sonoma does not have an adjustable distributor. If it was just a couple of degrees out, I could maybe wobble out the bolt hole and adjust it that way but it is out a lot. Most people that I talked to say that the balancer is on wrong but it only goes on one way with key-way on crankshaft. The timing chain marks were lined up with the dots being where they are suppose to be and having the #1 TDC on compression stroke and lining up the timing marks was also done. It runs like it is in time, minus the #6 miss and the P300 miss, but it starts good and cuts off good. I do notice however that it seem to miss a bit more radical on cold start and calm's down a bit after warm-up but still miss's. I am going to pull the exhaust from the catalytic converter today and see if that helps any.

There is a notch on the base of the distributor. That can be removed to allow more movement of the distributor. I have done that many times to get the correct reading.

As far as the balancer, that is why I asked to verify top dead center with the cylinder and then look at where the balancer is pointing.

Roy

Unless there is a way to take off the bracket from the distributor, which I do not see, then it cannot be adjusted. The Chilton and Haynes manual says it is not adjustable.

They are told to say that from the manufacturer. You can get around that.

Well I tried to figure out how to do it but with the base of the distributor being longer on two sides then it is on the other and the bracket is a U shaped fork type bracket then it is going to fit only one way with the long part being from 9 to 3 o'clock where the bracket bolts down to the manifold. Even if you somehow get the bracket off and adjust it, it is not going to fit back in the direction of the bolt hole. It does not have a round base.

It only has to move about one inch to get to the reading.

Roy

It cannot move period. The only way is to wobble out the hole for the bold and that might give you about 1/8, and that is a maybe.

Did you check the bottom gear of the distributor? They wear out a lot. The gears teeth got razor sharp from wear. That will cause the cam retard reading to be off.

Roy

It has new distributor, cap, rotor and yes I looked at it a couple of weeks ago and it was good.

We are missing something here.

Do you have a drivability issue with the engine?

Roy

Only the misfire on P006 and P0300 other then that it starts, runs, and I use it all the time.

Roy, here is what I got off of my scanner with live data:

Calc Load % 2.7
ECT F 178
STFT B1 5.52
LTFT B1 25.0
STFT B2 29.9%
LTFT B2 25 %
MAP inhg 10.9
RPM 641
SPARK ADV. 19.5
IAT F 59
MAF .6
02SB1 (V) .705
O2S B1 S3 (V) .48
STFT B1 S3 99.2
O2S B2 S1 (V) .82
STFT S1 28.9 %


See if you can make something out of it!

I assume you mean P306 and 300.

Okay, lets get off the timing as it has no effect on the codes.

You need compression, spark, and fuel for the cylinder.

Check for any vacuum leaks, the injector could be the issue. If I not mistaken, this has the spider under the plenum. Is that correct?

Roy

Yes it does, and when I had it in the shop last week they said that it had all three so they would say it is more mechanical. They said for me to look at the lifters and see if #6 was looking alright and so I did and so it is! They lift just as high as the rest on that side as far as I can.

Okay, another possibility is a broken valve spring. Look closely at the cylinder while it is running and see if the spring is broken. It will be obvious.

Another way to tell is to remove the plug and insert a compression tester and run the motor. See what the compression is while running.

Roy

And what should it be? The heads are redone with springs, valves, etc. I bough them from the Headshop who does this for a living.

Did you get the live data that I sent?

No, got nothing on data.

Should be at least 125.

Roy

You must of missed it, it is back about five messages ago. It is the live data from today.

Yep, you are right.

The long term trims pinned tell me it is running lean, very lean.

The first thing that comes to mind is fuel pressure. Beyond that, it could be mass air flow sensor.

Surprised you do not have a 171,174 code with those readings,

Roy