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'97 Sierra Z71 5.7L Vortec OBDII Codes

OBE

OBE

Member
Messages
129
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25
Location
Blackwood, NJ
Low mileage truck (97k gently-driven)

This truck has run perfectly for the two years I've had it but this Winter it began running rough on cold mornings. After it warms up to operating temp it's fine-as-usual. I read the codes and they are as follows:
P0172 (System too rich Bank 1) ...
P0300 (Random / Multiple cylinder misfire detected) ...
P0337 (Crankshaft position sensor A circuit Low) ...
P1345 ... Crankshaft position CKP Camshaft position CMP correlation.
Can anyone offer some guidance? I will move this to the correct forum if someone will direct me.

Will L. ...Well I can see the chain of events for the codes:
The 2 crankshaft codes are hinting to the issue i think. Then too much fuel dumping because of it causing the rich code and that causes the random misfires.
The cam and crank timing are reading too far apart. You need a scanner that can read the cam (cmp). It should be from -02 to +02. Anything out of that range and you need to figure out why it is out of time.
If this were an older non electronic small block you would just move the distributor to change the timing.
Was any work done on it back then when the issue started? Real high miles where the timing chain could have stretched?
It (problem) started in the cold... something to do with enfiching fuel via temperature- but I would think other codes would be present also...

Thanx, Will...I haven't had to do anything to it other than the trans which went on me and had to be rebuilt. Also had the worn brake line which I replaced. I had been talking about the way it seems to "use" coolant. I ran it real hot one time 'cause I was on the interstate and wasn't watching the temp gauge. It "seemed" to have come back from that, though.
I carry extra coolant with me and I watch the reservoir which calls for a drink every few weeks. I suspected the intake manifold gaskets allowing it to burn coolant since it never has any spot, on the ground, under it. Then one day I left it running while I ran into a place and when I came out I noticed dripping from the area at the back of the motor. It doesn't do it all the time, though, but it's getting rid of coolant from somewhere. I don't have a lift so I have trouble looking for the leak. I'm also 72-years-old, fat, and not very flexible anymore.

I went onto OBD-II Trouble Code dot com and got printouts of the codes. P0172, P0300, P0337, P1345. In those explanations they allude to oil or coolant getting onto the sensors as a possible cause. The truck began to run rough on early morning cold weather starts but when it warms-up it runs as good as ever. This truck had about 70k on the odometer when I got it and it's in the 90s now and the engine compartment looks like a new vehicle, so I doubt if engine wear could be the cause.

(please excuse the posting of an ongoing exchange...I had posted it in the wrong place and decided to move it)
 
I wrote-down all the error codes and then cleared them. The Check Engine light went out. I drove the truck on the Interstate for about 10 miles and when I got home I checked the "Pending Codes" and saw P0175 "System too rich Bank 2." Before clearing, I had a P0172: "System running too rich Bank 1."

Since the weather is warmer, I didn't get the rough idle when I started it this morning. My guess is that if I get a cold day it will run rough and trigger the error codes again; we shall see. I think it has something to do with the cold weather.
 
I'm going to guess you have multiple issues here. I know O2 sensors in these trucks can cause all kinds of bank rich or lean codes without setting an O2 code, and they will also set the P0300. But with it setting in both banks, my guess would be classic spider injection failure which will also cause rough running on startup. I would check the wiring for the crank sensor where it routes in behind the alternator bracket and inspect for chafes. You don't often hear of crank sensor issues on them, but it can happen to anything. As to the cam crank correlation, this code often sets when the distributor gear wears out. GM used a mellonized gear on them because of the roller cam required a hardened distributor gear. Many gears didn't get properly coated and fail. They will wear to the point they cause timing issues normally before they completely fail causing it to shut off. Most are replacing the distributor as gM used aplastic distributor in them, and they are known to crack when changing the caps. But if your crank sensor is failing, it can also throw your case learn off and set a code.
 
I've followed-up on your thoughts with some views on YouTube. Did you consider that this roughness occurs only at cold morning starts? If I let the truck warm up for ten minutes, it then purrs-like-a-kitten, and doesn't behave like anything is wrong EXCEPT that it gets-rid-of coolant @ about one-quart in a few hundred miles.

I want to approach this in a scientific manner but I would like to scale-in by degree-of-difficutly. e.g. I don't want to replace the spider if it needs a cap-and-rotor, wires & plugs. And I don't want to tune-it-up if the distributor is bad. And then there's that nagging coolant problem. I sense the sweet smell of coolant inside the truck and when I'm under the hood. And before the other day as it sat idling, I had never seen an leakage under the truck.
 
You mean the intake manifold gaskets that are a design flaw? Tell me...are these gaskets the ones under the throttle body? If so, it doesn't look (from the video I watched) that they would be such a big job to replace.
 
Thanx for the reply! Franken told me those engines have a quirk in that the intake gaskets were made of crap.
 
The vortec engines origanally came with plastic intake gaskets. If they haven't been done by now, I'm shocked it's made it this long. I've seen them crack and run coolant down into the lifter valley, run coolant down the ends of the block, but they can also crack and leak coolant into the intake runners of 1, 2, 7, and 8. Normally the intake gaskets leak the most when hot as that is when the system is under pressure. It shouldn't be hard to figure out whats going on. Let it sit overnight, start it for just a few seconds, shut it off, then pull the plugs and look for coolant or gas on them. You want to start it for a few seconds so anything in the intake runners will get pulled into the cylinder on the plug so you can see it. But a leaking spider or intake gasket won't cause crank sensor circuit codes, nor can they cause CASE errors.
 
Acdelco double platinum is the primary go to plug I run in them. They used to have an iridium, but I haven't seen them in awhile.
 
Sorry..."Fermanator", it is then. Tackling the easiest "fix" first (ala Ocham's Razor) I'll tune it up.

I notice something I've never noticed before: (perhaps it's because my old cars never had a .060 gap) but these plugs are all gapped @ .070 unless they wore-off .010 from the center electrode, and most of them had a build-up of carbon (or something) on the ground electrode similar to a stalagmite growing up from the ground electrode toward the center electrode. The center electrodes weren't excessively worn away and the plugs were, otherwise, in good condition.

One thing I picked-up from a YouTube video was that everything is original on this truck. I've mentioned before that it was pristine when I got it. All the hoses have GM markings and, since it had 60k when I bought it, it was probably never tuned-up. The spare still has lines on it like new tires before you drive on them a little while, and I think the tires are probably original. They are in need of replacement.
 
There is a white plastic clip on the end of a plastic line (that comes out of the harness) that clips into the rear bottom of the fuel pressure regulator. (I think) Is it important? It doesn't have any electrical wires coming to it but when I removed the air box and the air intake tube, it was loose (not connected to the rear housing of the regulator)
 
That little white clip goes into the spider injection plug to lock it in place. As to your plugs, that sounds like normal wear for single platinum plugs which is what came stock in those trucks. Only the center electrode got a piece of platinum on it, so .010 wear is completely normal for 100k miles. I've seen them open up to well over .100 once the platinum burns off and they really start wearing out. As to the carbon, that is pretty common to see with spider injection and/or bad intake gaskets.
 
Good stuff, as usual, Fermanator. I'll do plugs, cap, and rotor. My wires look great. They even have cylinder numbers on them. Unless you think renewing wires is a must. I'll check to see if the rotor has any "play" in it before I go to Advance A/P.

The cap and rotor is about $65 but a new distributor (which comes with a cap and rotor) is $158. Plus, I'd get a new cam sensor with a new DIST.
 
OBTW: I looked through my papers and found some work orders that came with the '97 Sierra.
Second owner bought it from a dealer in 2006 @ $13,409 Truck had 51,482 miles.
It's almost as though the dealership told him to get rid of it 'cause stuff was going to start breaking.
Third owner bought it in Summer 2012 Truck had 71,000 miles.
He had a lot of trouble with it:
Aug 2012 Lube & Oil change, recharge A/C system, serpentine belt, fuel filter. $670
Sept 2012 replace A/C Compressor, drier, cycling switch. $827
Oct 2012 Upper Intake Manifold Gasket, Fuel Pressure Reg, oxygen sensors. $729

He sold it to me in Spring 2013 for $4600. Truck had 75,000 on it.
I guess he thought it was going to drain him! lol

I changed the oil (like a good little truck enthusiast) and now it "knocks" after first startup of the day.
In Nov 2013 the tranny went.
My guy gave me that big, round, geared drum that strips due to the OverDrive issue, as a souvenir! lol $1700 :-(
Blew-out the brake line, that runs along the frame, under driver's seat. Another fault, I'm told "they all do."
I don't think I ever noticed the "knock" before the tranny got rebuilt. Don't know if THAT had anything to do with it.

These Chevys got a lot of design flaws.

If my damn "pot" stocks would take off I'd by a RAM Pickup! lol
If Hillary had won, I'd be rich by now! HAHAHAHA!
 
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