P0340 code on my 1999 C2500 Suburban

[travis]

When I left work this morning my Suburban started shooting ducks at light throttle between about 1700 and 2500 rpms. When I finally got out of the city and out onto the 60 mph roads, it seemed to be running ok but then would randomly jerk hard and was definitely down on power. My suspicion was it was fuel related, so when I got home I shut it off and went and dig out my scan tool and fuel pressure gauge. Started the truck back up and was reading a little low at idle...about 50psi. Drove around trying to duplicate this mornings issue and it run perfect, fuel pressure varied between 54 and 60psi, and idle went back to 52-54psi like it always has. I plugged in the scan tool and only got 1 code...

P0340 cam position sensor
A circuit bank 1 or single sensor
Replace engine 1 fuse
Replace VCM
Repair O2 sensor wiring
Replace distributor assembly
Replace cam position sensor

I cleared the code, then tried multiple times to get it to repeat and couldn’t.

Should I be looking at replacing the whole distributor assembly asap? Driving in heavy morning traffic with this issue was kind of interesting...

[motionper]

that vehicle needs to have the timing set with a scan tool, did you do this??? otherwise it will set a code p0340

[travis]

I haven’t touched the distributor in probably 2 years...it has never done this before.

[CGT]

Well the cam sensor is the distributor on that engine. That's the direction I'd be headed....inspection of the distributor...cap etc. They are semi-problematic. And as mentioned if you didn't know, the distributor has a fixed clamp(not adjustable) attached to it and ignition timing will have to verified with your scan tool.

I have had pretty good luck with the aftermarket replacement distributors made of aluminum surprisingly(OE distributor housing is plastic)

[BLstangin]

If this is a 5.7 which i suspect it is, the distributor is in fact adjustable but it is a very small range, you have to use a scan tool and set the distributor, which i believe the scan tool will show as cam retard, to 0 degrees within 2 degrees either way. A lot of times what happens is the distributor gear wears out on these older engines and the timing gets way retarded and causes the problems you have and you will find there won't be enough adjustment to get it back into spec. If the gear is bad go to to the gm dealer and order a new gear, the acdelco/GM part number is : 10457356

[In-Tech]

Can also be timing chain/gears.

[Schurkey]

If this is a 5.7 which i suspect it is... ... If the gear is bad go to to the gm dealer and order a new gear, the acdelco/GM part number is : 10457356

Yup. Strangely, a '96--'98 7.4/454 requires a different gear. I have not checked them side-by-side, but I suspect the gear is shorter to make room for an additional washer that the other distributors don't use. Gear, washer, thrust washer, and roll-pin are AC-Delco p/n 10457708.



https://www.summitracing.com/parts/ado- ... refilter=1

The camshaft retard code should be P01345.

[motionper]

in your first post it says you changed the distributor the i answered and you say the distributor hasn't been touched in two years, which is it????

[travis]

in your first post it says you changed the distributor the i answered and you say the distributor hasn't been touched in two years, which is it????

I copied what the scan tool read out...the code and suggested fixes.

It is the 5.7L L31 Vortec engine. I guess as soon as this near freezing drizzle stops I’ll go yank the distributor and have a look, and check for timing chain slack too.

Thanks for the suggestions!

[makin chips]

It is possible to change just the CMP sensor on those Vortec distributors. If you get a new one, make sure you order one with an aluminum body and not the plastic that they've always used that likes to crack at the cap mounting holes. I believe the one I bought @ O'Reilly was a TechSmart made by Standard Motor Parts? I'll have to check and be sure. It was nice not having to replace the distributor last time I did the ignition. Usually, I have to replace it every time because the ears crack and break off and reattaching then never works.

One thing to also check is the CKP sensor. P0340 says a faulty crank sensor could also cause this condition. I had this code on my personal vehicle with Vortec engine and never could get it to go away. It was to the point that I could watch it tach out at 99999 rpm on the Snap-On Verus scanner when it would hesitate but I never did figure out what was causing it. The engine was replaced a while back with a new GM longblock and the problem just happened to disappear lol. I'm convinced I had too much play in the crank front to back. I check it at one time but forget what it was at. I can tell you I was glad to get that fixed.

[makin chips]

in your first post it says you changed the distributor the i answered and you say the distributor hasn't been touched in two years, which is it????

I copied what the scan tool read out...the code and suggested fixes.

It is the 5.7L L31 Vortec engine. I guess as soon as this near freezing drizzle stops I’ll go yank the distributor and have a look, and check for timing chain slack too.

Thanks for the suggestions!

Don't forget to mark the distributor in both places before you pull it. I did once, while replacing it. I had a hell of a time with that screwdriver trying to find the right spot to put the oil pump tang.

[travis]

After all the issues on March 1st, I never could get it to happen again...until this morning leaving work. Gas mileage and power have definitely been down all week though (not that it has ever been “up” ), but with temps in the low 20’s I haven’t been real motivated to work on it. Today I replaced the cam position sensor and the crank position sensor (it has always randomly thrown a crank sensor code). The crank sensor had a nasty groove worn in it (that can’t be good). It sounds and runs soooo much better now. Still under powered though

When I put the scan tool on it before changing the sensors, I had it graphing the ignition timing...it was all over the place, normally running around 22.5* but spiking up and down between +48 and -65 at idle

I measured cold cranking compression on the front 2 cylinders of each bank and got 145-150 in each hole. I really expected another 20-30 psi there. Is this in the ballpark for a stock L31?

My scan tool does not read crank offset. It’s a Bosch unit I got from O’reillys (the best one they had). To properly set the timing, I guess I need to get another scan tool? From what I have been reading online, the idle timing readings I am getting are normal. But, if the distributor isn’t in quite right, would it still read correctly?

[Schurkey]

My scan tool does not read crank offset. It’s a Bosch unit I got from O’reillys (the best one they had). To properly set the timing, I guess I need to get another scan tool? From what I have been reading online, the idle timing readings I am getting are normal. But, if the distributor isn’t in quite right, would it still read correctly?

Seems unreasonable that the scan tool won't read cam offset. Sure they aren't calling it something else?

My ancient MT2500 "Red Brick" will read cam offset, and the thing is old enough to buy cigarettes.