Ignition timing on Silverado

Maintenance/Repairs
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21

Sunday update, hot off the press…

Found this link:

http://www.gmtruckcentral.com/articles/distributor.html

and followed directions on distributor position. Now starts and runs without P1345 fault. Engine put up a P0341 fault for cam position sensor fault and we replaced the sensor. Now no faults and idles nice when first started. After a few minutes and some tapping on the gas pedal, trying to get it to run in gear, it runs really rough and smells like gas near the exhaust.

No fault codes yet. It reminds me of when my EGR on my TBI 95 chevy truck was bad. Might look into the EGR now.

It seems like the ignition and cam timing issues might be past us. Unless the cam sensor has to be “learned” by the ECM.

I will update as we learn more.

22

does this truck has the CPI injection with the infamous spider manifold? I thought the vortecs had that going for them.

23

yup

I’m really getting tired of the 10 character minimum

@cdaquila can’t we eliminate that requirement?

1 Like
24

Day 3 under the hood. EGR seems fine, back to P0341 Cam Position Sensor Fault and P1345 Cam/Crank fault. Crazily enough, my son says that just before we had rod bearing issues it ran very poorly, and describes it like fuel pump or fuel system symptoms. More investigation to do here.

Seems like going in circles! I might check with an old acquaintance to see if he can have this heap towed to his place of business and get it on a Tech 2 Scanner and do some real diagnosis.

Will update as things go along. Keep the ideas coming if you can cope with this project!

25

It sort of sounds like you may still have some valve timing issues there OP. If the intake valve isn’t closing soon enough the compression stroke will send some raw fuel out the exhaust pipe. Of course if you got an intake valve that’s incontinent, same thing. But I’m assuming the basic engine structure is ok. Have you done a compression test yet?

26

When we rebuild the engine we lapped all the valves and put new seals on. In that process we had to disassemble the completely. It seems loke we are covered there. The bottom end has new pistons and rings. I watched my son as he followed the instructions to set the valves. Exhaust adjusted after the intake is almot closed and intakes adjusted as the exhaust is just opening. Took slack out of that cylinders valvetrain then cranked her down 3/4 more of a turn. I think the engine is ok mechanically and that is what is leading me to a fuel system problem.

Good ideas to check, though!

27

Whenever I do the 3/4 turn thing it is wrong. Tried it twice and had to back them off. I hope it ends up right for somebody.

28

Well we did the valves when I assume, the lifters were not full if oil. Si maybe they are too tight??

29

too tight could definitely send raw gas out the exhaust pipe. That’s a pretty easy thing to check, right, just remove the valve covers? If they are too tight it’s a good thing it won’t run, b/c running the engine w/ too-tight valves could ruin the exhaust valves and/or valve seats from overheating. A compression test might be able to suss out overly tight valves.

30

Hi All,

Latest info on the project:

Runs much better, put new ignition module on coil and new distributor. Fixed Cam Sync/Retard issue with Tech Tool by cashing in a few favors.

Now we have a Cylinder 2 Misfire P302 fault that keeps occurring and causes rough running. With a rebuilt engine and tight valves, new pistons and rings, head gaskets and head bolts, I can only think it is the fuel injection system.

Could it be the injectors or the “spider” in the intake?

31

I would lean more towards the injector. Swap coils and see if fault changes to a different plug?

32

Congratulations!

As to that persistent #2 misfire . . .

Yes, it certainly could be a problem with the fuel injection system

If you’ve still got that Tech2 scanner you mentioned, you could easily determine that, using the injector balance function, in conjunction with a fuel pressure gauge hooked up to the test port

That said, a high level aftermarket scan tool, such as a Snap on solus, for example, will also be able to perform this function test

As you know, swapping injectors, for the purposes of confirming a stuck injector, is pretty much impossible, due to the nature of the fuel injection system

One of the poppet nozzles could certainly be partially or completely plugged, as this truck is 20 years old

The good news is that fuel injector cleaner will sometimes clear them up. If you determine that #2 poppet is indeed clogged, I recommend you run the engine on fuel cleaner hooked up to the test port. If’s more effective than dumping a can of junk in the gas tank. The stuff you hook up to the rail is much more potent, anyways

But before you do that, I’d perform a compression test on #2 cylinder, just to rule out a mechanical problem

And if you determine a poppet is clogged, and you are unable to clear it up, the standard procedure is to remove the plenum, and replace the fuel injection assembly with an updated part, which replaces the poppets with mini efi injectors. The cost is actually not that bad, under $300 if you shop around.

33

db4690, I took your advice and found a compression gauge. #2 was at “0” psi. I checked the gauge on a cylinder that appeared to work and found 140psi.

Then figured:

  1. The first round of problems pointed towards head gasket sealing problems after the engine failed the smoke test.
  2. With new bolts and Felpro gaskets the second time, as well as checking with straightedge and feeler gauge for flatness of block and head, it could not be the head to block seal.
  3. The pistons and rings are new and gapped OK. Can’t be them.
  4. The valves checked OK after lapping and filling the intake and exhaust runners with mineral spirits to check for leaking valves (not scientific but, eh, its all I had!)
  5. Maybe it is the valve adjustment…despite setting it according to the service manual and having done it like this for years…and why just one cylinder???

So, I backed-off the intake rocker completely and put my finger next to the sparkplug hole while engine was cranked. No feeling of sucking or blowing air.

Then backed off exhaust rocker, cranked engine and viola! the exhaust valve must have been way too tightly adjusted and held open while running! Not sure how this thing got mis-adjusted twice, except that the exhaust lifter on #2 must have some other problem that makes you crank the rocker down too far to take the slack in the valvetrain, and maybe the internal works in the lifter plunger. Then when it pumps with oil it holds the valve open???

Anyway, adjusted both intake and exhaust really loose, started engine, ran like a top, and adjusted both while engine was idling.

The truck runs great now… Geeze, what a trip!

Thank you all for the help and ideas, especially db4690 and GeorgeSanJose for the compression test and valvetrain ideas!!

1 Like
34

Congratulations on a job well done!

Sounds like the truck is behaving normally now :slight_smile:

We all make a pretty good team, even though we’ve never met in person

35

Congrats on sticking with it. Good to hear you’re got your truck purring like a kitten again. Best of luck.

36

While I didn’t contribute to the solution (I saw no need), I feel compelled to compliment you on a job well done. Congratulations.

Happy motoring.
TSM

37

Thanks everybody! We have 150 miles on it now and it just plain RUNS! It is great and my kid is the happiest I have seen him on months.

1 Like
38

Vroooom!!! A kid with a smile on his face, nothing better than that.