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Old 02-09-2006, 12:31 AM   #1
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LT1 knock sensor is picking up knock, giving me bad spark retard and timing

Big problem.

Running tts datamaster to see my data. I really notice the problem while driving about 25 mph and stomping on the gas pedal. The engine sounds like marbles in a spray can or really bad timing. I dont have a laptop (only a desktop) so i cant see that data while driving. While parked i rev the engine and sometimes hear something but almost always the datamaster program picks up spark retard of up to 8 degrees max. Only happens if i rev the engine quickly. Usually start to see it around 2000 rpm. Doesn't matter what temp the engine is. All the sensors appear good except IAC=0.

It could be false knock but i dont know why. No codes being thrown. I'm running 91 octane, no exhaust pipes are hitting the frame. I've swapped out the knock sensor and knock module, still there. Running a LT4 knock module. Checked fuel pressure - 42 psi. Tested ignition coil - it is good. I have new spark plugs and wires so i'm not suspecting them much.

Other than this problem, the car runs great. Sounds great at high rpms down the highway.

Any advice or anyone had problems with spark retard with their LT1??

My next suspects are the opti, fuel injectors. Try to fix the IAC. One thing i did do is put in slightly smaller bolts in the motor mounts, can't rember why, think i lost a bolt and couldn't get bolts. Should i suspect that?

Last edited by Firebat; 02-09-2006 at 01:36 AM.
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Old 02-09-2006, 01:04 PM   #2
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Did you also put the LT4 knock sensor in? The ones for the LT1 and LT4 are totally different.

If you aren't running any of the Hotcam or LT4 swapover, why did you put the module in for? There is no added benefit of doing that which may be causing all of your problems.
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Old 02-09-2006, 01:18 PM   #3
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i have the LT4 knock module in right now, and when i swapped it back to the LT1 km, no difference. The LT4 km is just a better knock module which was designed to pick up less false knock. No, i probably didn't need it yet since i just have bolt-ons right now.
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Old 02-09-2006, 02:12 PM   #4
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I'm not referring to the module in the PCM, but the actual sensor on the engine, the two have to be swapped out to be compatable with each other.
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Old 02-09-2006, 02:23 PM   #5
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Re: LT1 knock sensor is picking up knock, giving me bad spark retard and timing

Quote:
Originally posted by Firebat
Big problem.

The engine sounds like marbles in a spray can or really bad timing. I dont have a laptop (only a desktop) so i cant see that data while driving. While parked i rev the engine and sometimes hear something but almost always the datamaster program picks up spark retard of up to 8 degrees max. Only happens if i rev the engine quickly. Usually start to see it around 2000 rpm. Doesn't matter what temp the engine is. All the sensors appear good except IAC=0.

if you can hear the engine making strange noises, I'm going to go out on a limb here and say its NOT false knock. my guess, you're pinging the **** out of it.

running stock compression?

what gas are you running? *nevermind, just saw the 91 octane*

any computer tuning?

the PCM doesn't just pull timing for random reasons. SOMETHING is causing it and you need to find out why. Get an automotive stethescope and listen to the engine with the car parked. Listen to every single part you can reach. Rev it up a little and do it.
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Old 02-09-2006, 02:40 PM   #6
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My mechanic said something about a base timing. Is there such a thing? Could the base timing be off?

I ran the car with the pretty much the original tune also before, just had a few things shut off like egr, air. It didn't seem to have as much pinging or whatever but it still was there and very annoying.

Last edited by Firebat; 02-09-2006 at 02:42 PM.
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Old 02-09-2006, 02:42 PM   #7
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has the computer been touched? if not, then no. unless something in the timing set or the cam was installed just all FUBAR'd.


just caught your edit. if it was pinging before the computer was ever touched, you can be sure its not PCM related. sounds like something mechanical to me.
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Old 02-09-2006, 02:43 PM   #8
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i did have to repair/socket my pcm because i had a programming error while trying to program it before.

Edit: Going to try swapping out pcms from my brother's car. 95 TA.
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Old 02-09-2006, 02:54 PM   #9
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Quote:
Originally posted by Klortho
I'm not referring to the module in the PCM, but the actual sensor on the engine, the two have to be swapped out to be compatable with each other.
The sensor is an Lt1 sensor...and i did not know that
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Old 02-09-2006, 07:46 PM   #10
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Quote:
Originally posted by Firebat
The sensor is an Lt1 sensor...and i did not know that
The LT1 and LT4 knock sensors are the exact same sensor. All it does is sense knock. It's the same knock sensor thats been used on many GM motors. it is the knock module on the PCM that is different. If you already have the LT4 knock module, unless the sensor is bad, you won't gain anything by changing it.
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Old 02-09-2006, 08:35 PM   #11
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I looked up the part number for the knock sensors, and they are different.

1995 Trans Am is a Wells part SU150

1996 Corvette Grand Sport Wells part SU121
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Old 02-09-2006, 08:35 PM   #12
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Quote:
Originally posted by Coach Hawk
The LT1 and LT4 knock sensors are the exact same sensor. All it does is sense knock. It's the same knock sensor thats been used on many GM motors. it is the knock module on the PCM that is different. If you already have the LT4 knock module, unless the sensor is bad, you won't gain anything by changing it.
not entirely true. LT1's from 93-95 used a different sensor than 96-97 LT1's. And the LT4 started in 96...

Anyway, its not causing my problem...
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Old 02-09-2006, 08:39 PM   #13
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I don't know, unless he has the tune advancing a bunch. I'm running 46* at WOT and have no ping even running 89 octane fuel.

If you want to Firebat, send me a copy of the .bin file and I'll look at the timing tables and see what he has it set to and compare it to a stock tune.
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Old 02-09-2006, 08:41 PM   #14
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Quote:
Originally posted by Klortho
I don't know, unless he has the tune advancing a bunch. I'm running 46* at WOT and have no ping even running 89 octane fuel.

If you want to Firebat, send me a copy of the .bin file and I'll look at the timing tables and see what he has it set to and compare it to a stock tune.
But if i program in the stock tune and drive it, it does the same thing but just not as bad...still really bad though.
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Old 02-09-2006, 08:42 PM   #15
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Did you get to swap out the PCM with the other one you were referring to?

I have another PCM that was damaged, it got wet inside and when I plug that one up, I can't even get to it with the laptop, but it will start the car, and miss like crazy because it has a bad program on it, it's possible that something else might have gotten damaged when the programming didn't complete.

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Old 02-10-2006, 03:50 PM   #16
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swapped pcms and programmed the other pcm with the same tune. Didn't fix it. It doesn't do it as much when cold.

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Old 02-21-2006, 04:49 PM   #17
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Not really hearing anything weird with the automotive stethescope.

To recap - Hopefully last problem to fix with the engine swap. Spark retard is seen in datamaster in open and closed loop while parked. The timing gets very bad when the car is warmed up when the accelerator is pressed quickly, even in park.
This is what is good: MAP, MAF, O2 sensors, spark plugs, plugwires, coil, fuel pressure, IAT, pcm, knock sensor, knock module, egr block-off plates/gaskets. The valve cover gaskets and intake manifold gaskets were replaced to fix the high idle problem (1500-2000 rpm) before this problem was found.

If the engine internals are good, what are the chances of it being the opti? I have a spare used optispark that i could put in...
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Old 02-21-2006, 05:20 PM   #18
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Try this, get Freescan and scan with it to get the actual knock count and see how bad the knock is.
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Old 02-21-2006, 05:35 PM   #19
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datamaster detects knock counts also... looking at the data - every time i rev it and pick up spark retard i'm also getting about 6000-10,000 knock counts added on. But i do have freescan too, just haven't used it as much.
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Old 02-21-2006, 05:36 PM   #20
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Ouch, there is definatly something going on with it, even after driving mine for 100 miles straight at 80mph I only have like 2500 total knocks. What plugs are you running in the car?

The opti itself wouldn't cause knock.
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Old 02-21-2006, 05:52 PM   #21
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I'm running brand new a/c delco platinum plugs. It could be possible the new plugs are bad but kind of doubting it. Then again, i did replace them.
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Old 02-21-2006, 07:06 PM   #22
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I would dump the plats and run NGK TR-55's in it. Just about everyone who is local runs them in both their LS1's and LT1's. I'm running them and they work great, just gotta make sure they're gapped at .050
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Old 02-21-2006, 11:28 PM   #23
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I'll put in some NGK tr-55's. It could very well be the plugs or wires even though they are new but its the only plugs i've ran in the LT1 since the swap began.

I forgot to mention that the exhaust smells yuck after i floor it...
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Old 02-23-2006, 11:23 PM   #24
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Put in the NGK's. Didn't fix it . I noticed that 2 of the old plugs on the driver's side had a lot of soot on them. Took off my driver's side header and could see that it had been leaking exhaust on all ports by the soot left behind. Who knows if it happened after i retightend the header bolts. The Hooker 2460 headers did not have D-ports and they are not smooth on the side that bolts to the head. I grinded and sanded down that side of the header to make it smoother. I had to do the same thing to the passenger header when it had a very audible exhaust leak.

So, put the driver's side header back on, didn't fix it.

Going to measure the resistance of the plug wires next and keep looking for exhaust leaks. Also, going to look into why the IAC=0 at idle, either the throttle adjustment screw is off or there is a possible vacuum leak, IAC should equal 20-40 at idle.

Note to anyone doing an LT1 swap - dont get Hooker Headers, go with Hedmans.

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Old 02-24-2006, 02:18 PM   #25
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Update- checked fuel pressure regulator and check for leaky injectors. They were all fine.

Ran the car at idle. The IAC slowly fails to 0. Can't be adjusted with the throttle stop screw. This would probably mean a vacuum leak after the tb but maybe its something else.

BLMs on both sides read 108 when car is warmed up.

Car is running rich i think, i'm going to change the oil next since i smell gas in it.

I'm thinking vacuum leak, so probably going to re-do the intake manifold gasket, again.

until then any other ideas/comments?

edit: Changed oil and re-sealed the intake manifold gasket. Its still running rich and the pcm tries to lean it out as much as it can (blms at 108). IAC is reading better, its at least not zero. The IAC jumps around 13-22. Its at 13 when it goes out of closed loop and goes into open loop. Then when it goes back into closed loop it slowly increases. The O2 sensors are not acting the same either, i just noticed...and the O2 is shutting down probably causing it to go in and out of closed loop.

edit2: Measured resistance of plug wires - nothing unusual. Replaced Injector O-rings, all 16 of them, the bottom 8 didn't look that good. Replaced Fuel pressure regulator. I guess if you smell gas at the vacuum line for the fpr when that line is removed then the FPR is bad. Replaced both O2 sensors also since one was bad. Engine stays in closed loop after reaching 140 F degrees now. Still runs rich at idle while the pcm is trying to lean it out as much as possible...

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Old 03-08-2006, 05:54 PM   #26
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Compression was in the range of 170-175 on all 8. I had the engine warm, throttle blades wide open, all spark plugs removed, coil disconnected, fuel injector electrical connections disconeected, 4 strokes for each reading. Does that seem right. My friend says to let it have more strokes until the pressure can't increase anymore...is that a better way to measure compression??
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Old 03-10-2006, 03:11 PM   #27
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Did another compression test, except 5 strokes each time to a cylinder. The values ranged from 174-182, so not too bad. Would it be worth my time to do a leak-down test? I just can't figure out why its running rich.
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Old 03-14-2006, 10:21 AM   #28
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I'm not an LT1 expert (I run a SuperRam), but a lot of the T/S stuff applies to either.....

Is there any chance you have a leaking injector? Have you looked at all 8 plugs since going to the new ones? They should all look the same.

One thing I know someone else found was a bad ground between the heads and the chassis. Was causing him to have to run different sized injectors to get his BLMs and AFR to come into line.

These are LT1 heads on a factory LT1 block, right? Just checking since I've seem some posts about the LT1 intake not lining up well on Sportsman II heads like I use.

Are yiu sure the exhaust is all sealed up correctly on both heads as well as the Y-pipe? A leak before the O2 sensors can allow extra air in make the engine think it's too lean and hence add fuel.

Hope I'm not insulting your intelligence with this post. That would be pretty easy to do with my limited knowledge of the LT1/LT4 Gen II blocks....
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Old 03-14-2006, 12:10 PM   #29
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I've pulled the fuel rail off and the injectors don't seem to leak. Plus, it takes some time for the fuel pressure to drop after the engine is off and the car always starts with no problems.

The plugs looked similar. Were covered in soot or oil.

I dont have the ground strap connected to the coil like the stock LT1s, but i took a resistance measurement and had 0 ohms from the ground of the coil to the frame.

Stock aluminum LT1 heads on stock LT1

I hope i have no more exhaust leaks. But the pcm/ecm is subtracting fuel, not adding it.

something i did yesterday was remove the MAF. The car runs on Speed density mode without it. It ran at idle but when i gave it any throttle it died. Thats not supposed to happen. So, proved again the MAF is good or not the problem.
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Old 03-14-2006, 12:19 PM   #30
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Spark plugs covered with oil? That means you have either blowby on the rings, or the valve stem seals are leaking oil, which I'm not for sure if this would cause spark knock either.

I had been running 89 octane in mine and noticed mine running extremely rich, putting alot of smoke out when I got on it hard. Today I need gas, so I dumped a can of Seafoam in the tank, filled it up with 93 and....no more smoke, and less way knock counts on the datalogging. You may want to run some concentrated injector cleaner through to make sure one isn't partially clogged, not letting enough fuel going through.
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Old 03-14-2006, 12:23 PM   #31
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Is seafoam sold in stores? I put in SLP injector cleaner stuff before, long time ago.
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Old 03-14-2006, 12:27 PM   #32
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You can get seafoam at Autozone, it's like 5.99 a can and has a variety of ways of cleaning. Sucking it into the engine with the brake booster line to clean carbon out of the combustion chambers, putting it in the oil to clean the bottom end out, or the tank to clean the fuel system.

Just follow the directions on the can, and you should be fine.
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Old 03-14-2006, 02:24 PM   #33
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Been doing some more thinking on this, hope you don't mind my comments.

1. When you said you used smaller bolts in the motor mounts, do you mean smaller diameter? If so, that could defintiely be a knock like kind of problem. If the motor is rattling a bit inside the mounts from the normal engine vibration, the knock sensor could be picking that up. Have you revved it up from under the hood to try and see where the noise is coming from? I'd look real close at those mount mount bolts.

2. Are all 8 plugs looking the same? I know you said similar, but just confirming its on all 8 of them since that would indicate a system wide problem of some kind as opposed to individual cylinders.

3. Even though you tried another ECM, you still downloaded it with your BIN. Is it possible to see what would happen with a stock binary loaded on another ECM? Maybe your binary has gotten FUBAR'ed somehow.What's different between yours and a stock binary, and why? Has this binary ever worked with the motor set up exactly like it is right now?

If the plugs really are all the same and this is a BIN that worked fine in your car previously, then it's obviously getting too much fuel for the amount of air it's receiving. So either the air usn't getting there or the MAF isn't reading it correctly. But you say you reied a different MAF, right? And it was a known good one? (New doesn't always mean good).

When did this problem actually start happening?
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Old 03-14-2006, 02:43 PM   #34
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1. Smaller diameter because it was the only ones that would fit easily. I was going to put in bigger ones if the rubber part of the mounts stretched just a tad more.

2. I'll pull the plugs and look them over again.

3. Tried stock tune on 2 different pcms. I'm running a tune that is supposed to be better and not supposed to be as rich as the stock tune and its tuned for 91+ octane

4. It was a MAF from another LT1 car that runs good.

5. This has been happening since i swapped in the engine. It ran fine in the donor car but we never started the engine up in the donor car after its accident when it rolled.
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Old 03-14-2006, 03:04 PM   #35
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Ahh, the doner car was rolled? It's possible that if the engine was still running afterwards, and the car was on it's top, it could have damaged a bearing since all of the oil would have been in the top of the engine and the oil pump couldn't pump any oil. It's possible that what you are hearing is bearing knock instead of spark knock, and the PCM would retard the timing a bunch.
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Old 03-14-2006, 03:49 PM   #36
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Quote:
Originally posted by Klortho
Ahh, the doner car was rolled? It's possible that if the engine was still running afterwards, and the car was on it's top, it could have damaged a bearing since all of the oil would have been in the top of the engine and the oil pump couldn't pump any oil. It's possible that what you are hearing is bearing knock instead of spark knock, and the PCM would retard the timing a bunch.
and make it run rich also?

Added seafoam to oil, gas tank, and brake vacuum line. The seafoam seemed to make the car run smoother but didn't fix the knock problem. Not sure if it fixed the rich problem. Going to hook up the datalogger. The seafoam did point out an exhaust leak at the driver's side header but i've been told that doesn't cause the blms to be at 108. It doesn't help things either so i gotta fix that header and maybe gasket.

How bad would it be if its a bearing?
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Old 03-14-2006, 03:53 PM   #37
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What makes it run rich is the PCM dumping fuel to try and kill the spark knock.

I confirmed this earlier with a buddy of mine who knows the LT1's inside and out, and recommended me running 93 in the car even though it has a stock tune

Let me go throw my laptop on the car and check and see what my blms are.
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Old 03-14-2006, 03:55 PM   #38
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mines not dumping fuel, its leaning it out as much as possible and is still rich
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Old 03-14-2006, 03:58 PM   #39
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...

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Old 03-14-2006, 04:02 PM   #40
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Ok, my blms were at 128 with a blm cell of 16 and that was taking it up to about 4k or so, getting a little spark retard, but that's common without a load on it
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Old 03-31-2006, 12:31 PM   #41
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I got one guy telling me on another board that the pressure at WOT and priming the pump should be the same. Is he right or wrong?

And when the car rolled it landed rightside up if it makes any difference.
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Old 04-03-2006, 01:16 PM   #42
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That should eliminate the lack of oil concerns, but still doesn't rule out a bearing gone bad. Not likely to be the problem though.

I keep coming back to the smaller than normal bolts in the motor mounts. I'd try the "normal" sized bolts to make sure the knock sensor isn't reading a rattle where the motor is moving around a little bit due to the looser bolts.

Also - the knock sensor can pick up an exhaust leak and mis-interpret it as a ping. Seal the exhaust and check it again.

AFWIW - knocks will cause the BLM to dump in fuel to try and stop the pinging, which WILL cause the BLMs to go downwards towards 108. I think we need to figure out the knocks problem first, then se if we still have a fuel problem.
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Old 04-04-2006, 08:01 PM   #43
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Should have the exhaust leak fixed now. I also put in bigger bolts for the motor mounts. Engine is still acting the same.
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Old 04-05-2006, 02:49 PM   #44
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d@mn....

OK, so we're still getting the high knock counts and the BLMs are around 108? Make sure you have disconnected the battery for a few minutes before you do this test/log so the previusly learned info isn't causing a problem.
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Old 04-05-2006, 04:42 PM   #45
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A friend of mine used to run into the same issue when he had a cutout on his exhaust.

Open cutout and the car would pull 8-10 degrees of timing. Close the cutout and immediately the car picked up full power again and no timing retard...
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Old 04-06-2006, 11:47 PM   #46
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Thinking about taking it to a mechanic...What do you guys think? PM me if you want, don't want to get too off topic.

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Old 04-08-2006, 02:34 PM   #47
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If, from your posts, you deleted the EGR, there is a good reason for your engine knocking like crazy. GM programmers use EGR to dilute the mixture, and by doing so, can advance the crap out of the spark timing. Without the burned gas in the combustion chamber, your engine will not run as intended by the designers.

If you can, find CarCraft issue from August, 2004, page 96. There's a reply by a Mr. Al Cline of GM High Performance Engineering, Pontiac, MI. He details how EGR and PCM are used in the LT1 series engines.

Good hunting,
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Old 04-08-2006, 02:54 PM   #48
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EGR typically does not work at idle, and does not work at WOT which is where i'm seeing problems. And besides the last thing i want to do is add more gas to the rich mixture. Thanks for the suggestion though.
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Old 04-08-2006, 06:27 PM   #49
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Quote:
Originally Posted by 357mag
If, from your posts, you deleted the EGR, there is a good reason for your engine knocking like crazy. GM programmers use EGR to dilute the mixture, and by doing so, can advance the crap out of the spark timing. Without the burned gas in the combustion chamber, your engine will not run as intended by the designers.

If you can, find CarCraft issue from August, 2004, page 96. There's a reply by a Mr. Al Cline of GM High Performance Engineering, Pontiac, MI. He details how EGR and PCM are used in the LT1 series engines.

Good hunting,
Tim sends
That makes no sense at all, if this was the case, people wouldn't be deleting the EGR in the first place and the LSx based engines would have the same problem when they swapped over to the LS6 intake, which has no provision for the EGR.
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Old 04-08-2006, 06:38 PM   #50
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I'm thinking about raising the injector constant one half pound...
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