L29 454---Replace Crank Sensor

[RedBurb]

No, I didn't do a relearn.

I would not change it just becasue you haven't done so. Mine was all greasy, and probably is again. It's got almost 300K miles on it, and I'm not going to replace a part that's working fine.

I appreciate the advice to "leave good enough alone" which I often subscribe to (admittedly not so much lately). There is another element to this story that I haven't shared on this post which is also prompting me to act. Specifically I've been chasing down a "slight missing" at idle issue that isn't throwing any codes but is throwing my OCD into OD. So in addition to buying a brand new set of (8) injectors + pressure regulator (the fuel filter is already new, as is the distributer w/CAM sensor, the (2) CATS, the (4) O2 sensors, the plugs and wires, the IAC, IAT, the air filter, cleaning the MAF, etc., etc, .....) I figure what the hell, why not change out the $47 crank sensor while I'm replacing that leaking timing cover? Man, how freakin weirded out I've become over craving a silky smooth L29 idle.

The same OCD drove me to change out the rear main seal a few months ago which is a ball buster job if done by yourself on the ground with a K2500 hovering 8" above your chest. Replaced the oil pump and pan gasket while at it plus new seals for tranny and transfer + front differential cases...Happy to report not a single drop on the driveway since. Now curing that dam missing idle is on my Most Wanted list and I will solve it. Thanks for the input!

 

[Schurkey]

Wouldn't it be cheaper and more-efficient to diagnose the misfire instead of blindly replacing parts?

What is your fuel pressure?

Connect a scan tool, look at the individual cylinder's misfire history. Verify the sensor data, and the computer output data.

 

[454cid]

Wouldn't it be cheaper and more-efficient to diagnose the misfire instead of blindly replacing parts?

What is your fuel pressure?

Connect a scan tool, look at the individual cylinder's misfire history. Verify the sensor data, and the computer output data.

I think he's complaining about the same thing my truck does and has done for a couple 100k miles. When idling it feels/sounds like it has an erratic mis, but the pcm doesn't seem to see it. I have never had a knock count on any cylinder as check with my old otc scanner. I just ignore it since it seems to run fine otherwise. I would guess it would take looking at live data on a scope, but that's nothing I've ever had experience doing.

 

[RedBurb]

Wouldn't it be cheaper and more-efficient to diagnose the misfire instead of blindly replacing parts?

What is your fuel pressure?

Connect a scan tool, look at the individual cylinder's misfire history. Verify the sensor data, and the computer output data.

Indeed, blindly replacing parts is foolish. But when I go after a known issue requiring a deep dive, I track how much energy and oxygen it takes to get me there, and then evaluate the surrounding barnacles. Old crusty barnacles are readily knocked off. Special scrutiny is paid to those growing on the hull and jutting at the propeller. Young shiny looking ones are mostly left alone --why bother, something must grow in that space? The truck has $180K miles on it and was covered with crusty barnacles. I'm 95% of the way through cleaning her mechanicals up. The fuel pump will also be replaced. Most if not all of these mechanicals will eventually serve aboard a rebuilt L29 engine (almost done!). This Skipper is trying to squeeze another 40-50K miles out of the current engine (which will then also be rebuilt). The truck is a long term keeper. All-in this $4K truck will cost me $17-20K and will serve my objectives more faithfully, reliably, and much much longer (two engines = +500K miles) than a newer +$50K version. Yup, enough already, I also need to buy that $400 scanner! lol Thanks!

 

[RedBurb]

I think he's complaining about the same thing my truck does and has done for a couple 100k miles. When idling it feels/sounds like it has an erratic mis, but the pcm doesn't seem to see it. I have never had a knock count on any cylinder as check with my old otc scanner. I just ignore it since it seems to run fine otherwise. I would guess it would take looking at live data on a scope, but that's nothing I've ever had experience doing.

It does sound similar. Mine is a very faint miss that only occurs at idle. Most passengers wouldn't notice it even after pointing it out. And you can't hear anything unusual outside or inside the vehicle. Furthermore the engine runs strong and performs well and gets the normal & customary gas mileage (= really sucks). But I feel the miss and know something isn't quite right...The serpentine belt tensioner also hops up and down about + - 1/2" when at idle. A useful visual that helped ruled out, "maybe I'm just passing gas?!"

 

[454cid]

It does sound similar. Mine is a very faint miss that only occurs at idle. Most passengers wouldn't notice it even after pointing it out. And you can't hear anything unusual outside or inside the vehicle. Furthermore the engine runs strong and performs well and gets the normal & customary gas mileage (= really sucks). But I feel the miss and know something isn't quite right...The serpentine belt tensioner also hops up and down about + - 1/2" when at idle. A useful visual that helped ruled out, "maybe I'm just passing gas?!"

My tensioner moves a bit too, but I think it's less than 1/2".... maybe 1/4"? I've replaced the tensioner pulley, but the tensioner itself is original.

 

[Erik the Awful]

I've never been in a vehicle powered with a muscle-car era V8 that didn't have an unsteady idle. My '99 Suburban got close to smooth when I balanced the rods and pistons and replaced the injection spider.

 

[thegawd]

My 97 K1500 5.7 Burb had a miss like that and eventually it turned out to be the TPS. it only happened driving like 95KM/H but it was actually related to how far the throttle was opened. eventually I found out that my scanner had a TPS test and so I did it and watched the graph dissapear and then reappear with the throttle like 3/4 of the way open.... there was a break in the data and the truck read it like the throttle was closed.

 

[RedBurb]

My tensioner moves a bit too, but I think it's less than 1/2".... maybe 1/4"? I've replaced the tensioner pulley, but the tensioner itself is original.

Good to know your T moves around some too albeit less. This is the first L29 I've owned or driven in and therefore have zero frame of reference. But I believe my T was rock steady before I replaced the leaking intake gaskets and the engine definitely didn't have this slight miss at idle before that repair. I've re-torqued bolts, sprayed starter fluid at suspicious vacuum points(+- 0 rpm), replaced sensors etc. but my gut (OG pre-scanner) tells me a fouled injector(s) is the culprit. Hence an RockAuto injector set + regulator is on the way. For science sake I'm going to hold off repairing the leaking timing cover + replacing the crank sensor to test & confirm whether this hunch is right. If not I hereby swear to the GMT400 Gods I'll immediately buy a proper scanner tool with 300 page reference manual (which I'll promptly wrap and gift to my 40 year old son--it's his race car we're towing around after all! ;-) Thanks

 

[RedBurb]

My 97 K1500 5.7 Burb had a miss like that and eventually it turned out to be the TPS. it only happened driving like 95KM/H but it was actually related to how far the throttle was opened. eventually I found out that my scanner had a TPS test and so I did it and watched the graph dissapear and then reappear with the throttle like 3/4 of the way open.... there was a break in the data and the truck read it like the throttle was closed.

Interesting point. Not exactly the same circumstances but your comment does makes me wonder whether I might have an issue with how I reinstalled my cruise control cable recently and whether the throttle is now ever so slightly open...? Might this lead to a slight miss?? Something relatively easy to check in the morning. Thanks