Engine knock

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I have been out of town for a while but wanted to jump in on this thread. My 97LX450 seems to ping some on regular gas. From a start and under mild to moderate acceleration. It improved for about 3k after my headgasket was replaced. It returned over the winter. I agree with Rookie2 as it appears to be worse with temp changes. My truck does not knock at all with regular gas when I drive in higer elivation (North Carolina) but returns on the ride back and in Florida.

Until I can find out the cause for sure, I am running 93 octane and the minimum dose of RedLine fuel system cleaner. This seems to stop the problem and does not cost me much at this point (I get 93 on sale at local gas station on Fridays for same price a middle grade. I pay about what others pay for regular on busy roads).

This seems to do the trick but not sure why I have the problem. I suspect this is due to carbon buildup but, again, not sure why.

Thanks

Andrew
 
Pulling the cams for me wasn't a big deal. but I've done work like this before. To pull the cams you need to remove the distributor which most will have trouble the first time placing that back in and getting the engine going. It's not technically hard but it is exacting work. There are timing marks on the vibration damper, timing marks in the gears of the cams, all which need to be "timed" in order for the engine to run.

For something like this I use the FSM as a guide as it is written as if you are doing a full rebuild on the engine which you aren't and there are steps in there that need not be done.

I targetted the middle of the range as it's not that exacting because shims come in varying thicknesses about ever .002. Mine had all loosened so I measured the thickness of the existing shim and matched it to the closest factory one and then placed in the shim that was 1 thicker than that.

Because I needed so many Dan had them coming in from all over as no one depot had enough for the entire order. Because of this if your truck is up in it's age plan on 3-4 business days to get the shims in that you might need. I elected to next day air them, I ordered them on Monday morning and received then 10:30am Wednesday. The truck was running by 3:00 pm.
 
Andrewsreef said:
My truck does not knock at all with regular gas when I drive in higer elivation (North Carolina) but returns on the ride back and in Florida.
Click to expand...

Makes since. Less dense air = higher fuel/air ratio (richer). But I would imagine if you stayed at higher altitudes for a longer period of time, the ping would come back once the computer adjusts, since you haven't corrected the root problem.

:beer:
Rookie2
 
landtank said:
Pulling the cams for me wasn't a big deal. but I've done work like this before. To pull the cams you need to remove the distributor which most will have trouble the first time placing that back in and getting the engine going. It's not technically hard but it is exacting work. There are timing marks on the vibration damper, timing marks in the gears of the cams, all which need to be "timed" in order for the engine to run.

For something like this I use the FSM as a guide as it is written as if you are doing a full rebuild on the engine which you aren't and there are steps in there that need not be done.

I targetted the middle of the range as it's not that exacting because shims come in varying thicknesses about ever .002. Mine had all loosened so I measured the thickness of the existing shim and matched it to the closest factory one and then placed in the shim that was 1 thicker than that.

Because I needed so many Dan had them coming in from all over as no one depot had enough for the entire order. Because of this if your truck is up in it's age plan on 3-4 business days to get the shims in that you might need. I elected to next day air them, I ordered them on Monday morning and received then 10:30am Wednesday. The truck was running by 3:00 pm.
Click to expand...

Good stuff. Thanks for the info Rick.
 
I'd bet money that if we all pulled our heads, scapped the carbon off the pistons, then buttoned it up................there would be no more pinging.
 
Does this timing change from the 80sCool site include the 95-97 models? I'm asking this again because I seem to recall that the change to OBDII electronics that started in '95 means this timing advance will not work as the engine will simply correct back to the advance it's supposed to have. I'm aware of this mod and did it to my 93 years ago.

Can anyone definitely say this mod can also be used on 95+ FZ's? I don't have the 95+ electronics in my 93 FSM.

Thanks!

DougM
 
Mine was loaded with carbon when I had the head gasket done. Like I said the problem was corrected and no pinging for 3k but then it returned. So the question is, what is causing the carbon to build up so fast. My severe around town driving does not help but my wife's van does the same thing with no pinging. Something must be the matter with the fuel delivery system (lean burn) or the computer.

For now, my fix seems to be working so I am going to stick with it.

Thanks

Andrew
 
fzj80kidpen said:
Dryfly,
Dougs advice is good.
Couple techron, couple redline.
When I did it I never heard the pinging.
Has only just began to comeback now with the heat.

Aussies,
They put ethanol in our gas as well. Call it gasohol.
The way I understand it ethanol is used to increase octane. (less ping)
However more ethanol also decreases the overall BTU. (less mpg)

Bill
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That's very interesting to hear that, I have no idea the consequence of ethanol in the gas, though the Government stepped in recently and banned it from our gas as vehicle manufacturers were denying any warranty claims on engines as a result of using fuel containing ethanol.

Very touchy subject down here, and most gas stations here have big signs at the front which reads "No Ethanol used in our fuel" and "100% fuel sold here" etc, etc.

There were many engine problems as a result, which is why the government had to do something.
 
Doug, the computer has no idea where the mechanics are set. How could it? The computer assumes the machanic has correctly set the distributor to 3 deg BTDC. It then just advances the spark according to RPM and TPS position. If there is a knock from being to advanced it simply retards the spark.

This is very much the same as the old carb systems. The mechanical advance would adjust for the rpms, and the vacuum advance would adjust for throttle position.

I haven't had a chance to verify what has been posted from 80scool, but I beleive it is in error. And the advance that was seen after removing the jumper at idle was do to the fact that he wasn't idling at 600 rpms. I'm almost 100% sure that my truck reads identical with or without the jumper in place at hot idle. Which is what I'd expect from it.

In order to get proper timing you must be idling at 600 + 50 and the TPS must be adjusted in spec.

At least this is my inderstanding.
 
landtank said:
And the advance that was seen after removing the jumper at idle was do to the fact that he wasn't idling at 600 rpms. I'm almost 100% sure that my truck reads identical with or without the jumper in place at hot idle. Which is what I'd expect from it.

In order to get proper timing you must be idling at 600 + 50 and the TPS must be adjusted in spec.
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Unless I've totally misunderstood you, this is not consistant with what I've experienced, and what the FSM says. My 97 FSM indicates to check and adjust the timing with the above mentioned terminals jumped. Then under FURTHER CHECK IGNITION TIMING, it indicates with the jump out, that the timing mark moves in a range between 2 to 13 degrees at idle. And that's what I've experience +/-, the timing mark bobs around all over the place.

:beer:
Rookie2
 
I'll have to check, but I first shot a look with the timing light without the jumper in and it was steady and well advanced. I then jumped the pins and it was steady and in the same place until I adjusted it. I haven't gone back and rechecked it but will. I'll try and confirn tonight.


Just ran out, drove around the block and took a reading. I'd call it a flutter but that's it. It would depend on how stable the engine is idling. When I put the truck in drive it was almost completely gone. But even so, when in nuetral it was less than 1 deg.
 
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Rick,

Thanks. I'd thought the newer electronics could somehow use the crank position sensor, or some other electronic whosit to prevent owner molestation. Seems like that's how modern engines are these days and I figured the OBDII 80s were the same. I'll be advancing the 97 a few degrees soon, then. It's already notably peppier than its '93 sibling, so this could be interesting.

DougM
 
Rookie2 said:
Makes since. Less dense air = higher fuel/air ratio (richer). But I would imagine if you stayed at higher altitudes for a longer period of time, the ping would come back once the computer adjusts, since you haven't corrected the root problem.

:beer:
Rookie2
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The mass air flow sensor will read the weight of the incoming air not volume,

The lack of ping is likely due to reduced fuel air charge that can make it into the cylinder reducing pressure and therfore temprature on compression making it less likely to detonate.
 
IdahoDoug said:
Rick,

Thanks. I'd thought the newer electronics could somehow use the crank position sensor, or some other electronic whosit to prevent owner molestation. Seems like that's how modern engines are these days and I figured the OBDII 80s were the same. I'll be advancing the 97 a few degrees soon, then. It's already notably peppier than its '93 sibling, so this could be interesting.

DougM
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I think that is when you get into distributorless ignition systems. These things are just short of that.
 
Okay, I got off my lazy butt and went out and bought a timing light. Following the instructions above my initial timing reading was about 5 degrees. I shorted the two pins and my timing showed a steady three degrees. So timing is not my problem.

I will note that I could NOT get the CEL light to come on when I shorted the pins. I tried a paperclip and a wire. The timing definitely changed when I shorted the pins. I just couldn't get the CEL to flash. The bulb does work. Anyone have a similar experience on a 96-97?

To me my pinging sounds like a vacumn leak. I've checked the rubber intake for cracks and nothing else seems out of place. Anything else standard to look at? PCV is good and the plug wires are in factory specs....
 
Cylinder deposits?
 
IdahoDoug said:
Cylinder deposits?
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That's gotta be it. If the timing is ok, and all electronics working correctly i bet it's tight compression due to deposits. Just thinking out loud here.
 
If it is cylinder deposits, I'm guessing there isn't much of a truely effective way to clean the pistons without moving the head.

What about a dirty injector? Too little fuel in a cylinder but not enough to trip the CEL? The pinging stops once a load is on the engine.
 
If it were mine, I would attempt to capture real time the air fuel ratio and the actual ignition timing at the point in time the pinging occurs. There is software on the market the clainms to being able to do that. Less than $200 plus you need a laptop. Measuring timing at idle is a good measure, but doesn't guarantee that it is not running to far advanced when the pinging is occuring.

A good shop with a dyno and appropriate instrumentation could also shed some light.

Is there a possiblity that the pcv valve rattles under part throttle under certain conditions? Are there any other check valves under the hood that could do the same?
 
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