5.7 Vortec cold tap/knock HELP!

[99Classic]

No. The computer does not change the timing based on the cam sensor. The base ignition timing comes from the CRANK sensor. The distributor/cam sensor needs to be aligned with the crank sensor so that the rotor phasing is close--otherwise the spark could jump to the wrong distributor cap terminal. The computer uses the cam sensor to determine which cylinder is misfiring, and nothing else.

So, no, being way off on the "Cam Retard" or "Cam Offset" or whatever the scan tool calls it is NOT compensated-for elsewhere. It needs to be within tolerance (+ - 2 degrees.)


Got me beat. Only -20F overnight here, but with high relative humidity and 12 mph wind, the candyass wind-chill is considerably "colder"


I can't even picture that.

Yeah I'm up in Canada and with the wind chill she hit -58⁰ farenheit last night. Not too fun lol.

When I adjusted the timing we got it on the proper tooth but the closest we could get it was +6⁰ of cam retard after turning the distributor all the way clockwise. Maybe need another tooth clockwise then turn it back counterclockwise? Or would this be just gear wear? Bad sensor? Seems to run really good aside from having the original 230k mile plug wires.

On the lifter side of things, haven't had much time with school, work, etc. The sound isn't a knock per se. More of a hard hollow tapping noise. Only does it if its been sitting 4+ hours. So if the engine completely cools before that it doesn't do it. So not exactly temperature based.

Also the lifter plungers didnt push down when I was adjusting the rockers. 1/2 turn after pushrod lash was 0 gave me no compression, but 1/4 turn did. These new lifters seem to have decent travel in the plunger so I'd bet the old ones are still plugged up. I'd bet this entire issue is with the lifters.

Also lastly, the truck seems really sluggish lately. I know shes got quite a few miles but she just seems lower on power than she should be. Maybe the lifters are causing it. Same with the crap mileage at 9mpg combined.

Thanks for the info on the sensors and stuff, I just figured the timing was advanced automatically. Not getting any codes though for it being +6⁰.

 

[Supercharged111]

No matter how well you mark the distributor, it will be off a few degrees from where you are now which is likely not within spec due to distributor gear wear. The CMP is way more sensitive than setting timing on an older motor. From what I understand, the cam sensor gets you sequential EFI, so without the cam sensor the engine batch fires the injectors. I unplugged it and drove around and couldn't tell a difference at all.

 

[99Classic]

No matter how well you mark the distributor, it will be off a few degrees from where you are now which is likely not within spec due to distributor gear wear. The CMP is way more sensitive than setting timing on an older motor. From what I understand, the cam sensor gets you sequential EFI, so without the cam sensor the engine batch fires the injectors. I unplugged it and drove around and couldn't tell a difference at all.

Oh boy. So with the reading out of spec could that be causing my crappy fuel economy? I can imagine batch firing the injectors would cause her to drink fuel.

 

[CKVortec]

When I adjusted the timing we got it on the proper tooth but the closest we could get it was +6⁰ of cam retard after turning the distributor all the way clockwise. Maybe need another tooth clockwise then turn it back counterclockwise? Or would this be just gear wear? .

gear wear would cause the timing to jump around not be constantly off in one direction.
I think I saw from your previous posts that you replaced the distributor, was it aftermarket?
I found that two different aftermarket dizzys that I tried were mis-manufactured and could not be timed due to the limited amount that you can turn them on the vortecs with the plug wires sticking straight out both sides hitting the upper intake before you could get close enough. one tooth either way and it was either + or - 7 to 10 degrees or so. I found that if you remove the roll pin holding the gear on the bottom and turn the gear 180* and put the pin back in you are essentially moving everything 1/2 a tooth. Looking at it you will see that one end of the roll pin lines up with a tooth and the other lines up with a groove. then when you reinstall it you can dial it in properly.

 

[99Classic]

gear wear would cause the timing to jump around not be constantly off in one direction.
I think I saw from your previous posts that you replaced the distributor, was it aftermarket?
I found that two different aftermarket dizzys that I tried were mis-manufactured and could not be timed due to the limited amount that you can turn them on the vortecs with the plug wires sticking straight out both sides hitting the upper intake before you could get close enough. one tooth either way and it was either + or - 7 to 10 degrees or so. I found that if you remove the roll pin holding the gear on the bottom and turn the gear 180* and put the pin back in you are essentially moving everything 1/2 a tooth. Looking at it you will see that one end of the roll pin lines up with a tooth and the other lines up with a groove. then when you reinstall it you can dial it in properly.

Yeah it was an aftermarket one. Got it off amazon because money was tight at the time. 110$ for this one or 270$ for a remanufactured one so I went with the cheaper option. When I pull the intake to do lifters I will definitely try your method and spin the gear 180⁰. It seems right in that range that you mentioned and I could not turn the body any further because of the plug wires.

As Supercharged111 mentioned, the CMP retard being off, could that cause the batch firing injectors? Is that even something this injection system is capable of?

 

[Supercharged111]

I never saw a change in mpg when I drove with the CMP unplugged. If it's plugged in you won't be batch firing injectors.

 

[99Classic]

I never saw a change in mpg when I drove with the CMP unplugged. If it's plugged in you won't be batch firing injectors.

Okay, then I won't exactly worry about it much then. If it was causing bad mileage then I'd do something about it. Thanks for the info. It's nice to get some knowledge from you wizards!

 

[Erik the Awful]

I can imagine batch firing the injectors would cause her to drink fuel.

Back in the late '90s Nissan had a recall on the VG30 powered vehicles to replace the fuel rail hoses. Part of the recall was a new injector harness because the old harnesses were too brittle to reliably work after plugging them back in. Each injector had separate leads, but with the kit you tapped the middle injector on each side for the new harness and capped the front and rear injectors' wires on the car's harness. You essentially turned it from sequential-fire to batch-fire. It made absolutely no difference in how the cars ran.

What we tend to forget is that '90s automotive computers weren't fast enough to time fuel injection to specific cylinder events, and the injectors don't flow enough to shoot that large of a fog of fuel that quickly. If your injectors are running at 80% duty cycle, they're open 80% of the time, building a fog of fuel in the intake runner so that when that valve opens it can enter the cylinder. As far as I can tell, the new direct-injection systems actually work how we always imagined fuel injection works, but I'd welcome input from anybody who's actually engineered or been trained on the new systems.