Just a bad wire

[Drew Dowdell]

is it even sputtering?

[ocnblu]

Jeez, I hope it is something incredibly simple that's been overlooked, Camino.

[Camino LS6]

Well, it's running.

Not as well as it needs to, but that's good enough for me for today.

I'm spent.

Went through the whole valve/lifter pre-load adjustment process (which requires a bunch of disassembly) again, cleaned the soaked spark plugs (fuel), and advanced the timing dramatically.

It finally came to life.

Good oil pressure, and getting smoother as it ran, but the lower radiator hose sprung a small leak so I just called it good for the day.

[ocnblu]

Tahoe, I dub thee: Frankenstein. It lives!

[Justin Bimmer]

Yesssssssss!

Soon...

[Camino LS6]

I really don't like that I had to advance the timing so much. I'm starting to think that, in spite of the fact that I checked and re-checked, I might have gotten the timing chain a tooth off.

Not a great feeling, but it still beats a toasted cam and lifters.

I'll think about it tomorrow.

[Camino LS6]

I guess that I should also explain why I had to go through the valve adjustment again. The problem is that lifters as old as these tend to leak down which throws the adjustment way off. To compensate, I first loosened the rockers as much as I dared, then removed the plugs and spun the engine with the starter to build up enough oil pressure to keep the lifters full. I then rushed to loosen any tight rockers, and proceded to do the adjustment as quickly as possible. The alternative would have been to adjust them "hot" which is always a messy, unhappy way to do that. In the case of this engine, in this vehicle, it would also be nearly impossible - too much stuff hanging over , and next to, the rockers.

This was all a big gamble, and I'm very happy that it worked.

[SAmadei]

I used to have a spare, modified valve cover that I used to adjust the valves while running, which usually kept the mess down considerably.

[Camino LS6]

I used to have a spare, modified valve cover that I used to adjust the valves while running, which usually kept the mess down considerably.

Yup, know that trick. But doing that on anything with so much stuff around the valve covers isn't a pleasant alternative.

I hope to never adjust valves that way again.

[Camino LS6]

I may take a break from this today - my hands are hamburger, and other duties call.

The exhaust system should be waiting for me at Napa, and I'll need a new radiator hose, and a new gasket kit for the timing chain cover (yes, I'm going back in there). I think I'll do a fresh batch of oil and another filter now that I've had it running. As cruddy as things were in there, I think it would be a prudent thing to do. That, and to flush out any foreign matter that might have found its way in during the process.

This is starting to feel like cleaning up loose ends - and that's a very good thing.

[Camino LS6]

Picked-up everything I need to finish this off yesterday. I hope to have this project completed by the end of today.

[Camino LS6]

Exhaust is in - it was the usual battle.

A quick meal, and I'm going for the finish.

[Camino LS6]

Yeah, that mistake I thought I made?

Didn't happen.

The timimg marks were perfectly in line when I got back in there. So I put it all back together again and ran it for quite a while.

Still not right.

At this point it almost has to be a bad cam.

This project is now on hiatus until I can exhaust all other possibilities.

[Drew Dowdell]

how do cams go bad but the engine still runs?

[SAmadei]

how do cams go bad but the engine still runs?

A lifter wipes out a lobe... and you're running on 7 and half cylinders or worse.

Over time, all of the cam lobes wear down... some more than others.

[Justin Bimmer]

I don't want to drop the bomb, but ECU?

[Camino LS6]

I don't think ECU.

Most likely, this is a cam or distributer issue.

I will pursue the distributer possibility by starting from scratch and resetting it while at TDC.

If that doesn't get the job done, it pretty much has to be the cam - and I'm not going there right now.

I do find myself wondering if I might have changed the position of the oil pump rod when removing that plastic bit - that could have done it.

[Camino LS6]

how do cams go bad but the engine still runs?

A lifter wipes out a lobe... and you're running on 7 and half cylinders or worse.

Over time, all of the cam lobes wear down... some more than others.

And this cam has alot of time on it.

[z28luvr01]

Why not do the compression test now? If the cam is worn, I'd think the valves wouldn't be opening or closing properly, and that might show on a compression test.

I think JB may be onto something. I'd diagnose it as a potential electronic issue before jumping back into the engine. Put it this way, if there's a wire plugged into the distributor that eventually finds its way back to the ECU (and I'm pretty sure there is on the TBI 350), then the ECU and the sensors it gets its data from have a say in the timing. It can't hurt to eliminate it.

[Drew Dowdell]

Why not do the compression test now? If the cam is worn, I'd think the valves wouldn't be opening or closing properly, and that might show on a compression test.

I think JB may be onto something. I'd diagnose it as an electronic issue before jumping back into the engine. Put it this way, if there's a wire plugged into the distributor that eventually finds its way back to the ECU (and I'm pretty sure there is on the TBI 350), then it can't hurt to eliminate the ECU and the sensors it gets its data from.

this and this.

[Camino LS6]

Yes and no.

The compression test is a good idea that I'd like to do in any case.

I pulled the pigtail so the ECU had no say in the timing - the problem exists with, or without, the computer's involvement.

I think I am ging to find two things when I mess with the distributer.

1) That it is, indeed off.

and

2) That the problem will persist after I deal with that.

But rest assured, I'm going to try everything I can before that engine comes apart again.

[Camino LS6]

Confirmed.

The distributer was off, and correcting it improved things somewhat. I was able to set the timing to factory spec which was not possible before. However, the engine still breaks-up under any load (a quick rev or putting it in gear will do it), and the idle is still a bit rough.

But I have an idea.

[Camino LS6]

Inching closer?

Maybe.

I replaced a fuel filter that looked to be original (painted black and no markings).

That seemed to help a little bit.

Then I "ran it in" at 2500rpm for a long while. The missing seemed to come and go during that and the oil pressure and temp were rock-steady. Also, there is zero sign of either coolant or oil smoke in the exhaust (both of which were gett6ing pretty bad before I dove into this). I've since driven it around on the property quite a bit, but it still hates to be under load. It pops and sputters, but you can feather the gas to prevent that. On level ground it behaves pretty well, but it hates the hills.

Overall, it feels like it wants to run strong, but can't quite get there (if that makes any sense to you). I'm wondering if another set of fresh plugs might help as the ones I'm using are new but went through this whole process and could be compromised.

Not there yet, but headed in the right direction.

[67impss]

Ever do that compression test

It just seems that you're just fine tuning an engine with a problem that hasn't been identified yet. I know you are frustrated but go by the flow charts to fix the problem instead of chasing this rabbit. I know how bad I was chasing my tail when the ignition module failed partially (the fuel side failed) took me 3 days and my best friend(as good a mechanic as myself)2 days to find it 1.5 hrs to drive get the parts and repair.

Please don't take this wrong I don't mean to heckle you I really want you to get this fixed with the minimum time effort & $ expended

I'm trying to find the flow chart I used & will post a link when I find it Best of luck, Rick

[z28luvr01]

If the fuel filter helped, take a good long look at the rest of the fuel system. Try cleaning the injectors and/or replacing them. Should be fairly straightforward on a throttle body. At the very least I'd run a bottle of good fuel system cleaner on a tank of gas.

[Camino LS6]

I need to do two tests that I don't have the tools here to do.

1) Fuel pressure test

2) Compression test

I'm not really "chasing the rabbit", but I have been researching this and a great many things can cause the condition I'm seeing. The most likely, it seems, is the fuel pressure regulator in the throttle body - so I need that pressure test. Whatever is causing this condition is something other than the parts I have already renewed - it is a separate issue.

[z28luvr01]

Do you have an AutoZone near you? They'll lend you any tool they have, for free.

[Camino LS6]

None around here, but I can make a few calls...

[67impss]

Camino hears the site with the flow chart & troubleshooting info this is what I used http://chevythunder.com/

Best of luck, & yeah Autozone Advance & O'Reily's can help with loaner tools Autozone is free though

[Camino LS6]

Camino hears the site with the flow chart & troubleshooting info this is what I used http://chevythunder.com/

Best of luck, & yeah Autozone Advance & O'Reily's can help with loaner tools Autozone is free though

Thanks for the link, 67.

No Autozone,Advance, or O'Reily's around here - this is Pep Boys territory.

[A Horse With No Name]

I hate Pep boys-Don't like Autozone or Advance, pretty much like buying from O 'reily Auto parts....

[Camino LS6]

One option I do have is to swap-in parts from Mothertruck, I replaced most of the sensors when I did the engine in that truck. I may even have some of the old ones hanging around.

[Camino LS6]

Kind of boring, but here are some shots of the exhaust I did the other day. The one bad spot in the first pic shows repeated (and lousy) re-welding. As the rest of the system was also welded, I needed to replace everything from the cat on back. No holes anywhere else in the system - a bit annoying.

So, I thought I'd post these while I try to get my hands on a fuel pressure tester (it seems that you have to get a specific adapter for the TBI - which jumps the price, of course). More updates when I get the proper tools to procede.

[A Horse With No Name]

Keep the photographs coming!

[SAmadei]

You're description makes me think its leaning out. I would continue looking at the fuel system, but I would also double check there is no vacuum leak or mixed up vacuum lines.

[67impss]

Keep us up to speed. You can always bounce anything off me if your stuck(short of a wrench off the noggin)

[Camino LS6]

Thanks guys, and yeah, I've been all over it looking for a vacuum leak - found nothing.

[67impss]

WD40 trick works swell for that

[Camino LS6]

OK, here's what it isn't:

The fuel pressure regulator - I pinched-off the return line which would have caused a leak, or boosted my fuel pressure. There was no change.

The O2 sensor - took it out of the loop, no change.

A bad cylinder - pulled each plug wire in turn, idle degraded with each one.

ECM timing changes - problem exists with computer in, or out, of the loop.

Vacuum leak - have searched repeatedly and found none.

Coil - swapped-in a known good one.

Ignition module - lost patience and bought a new one.

I'm starting to think clogged cat.

[Drew Dowdell]

How much vacuum line is under there? It doesn't have to be the tubing that is cracked, but one of the connectors. Also, the tubing can be clogged.

Buy a small spool of it, replace it all, and the connectors.

[67impss]

Clogged cat will show it's self at high speed & with a hot cat. unbolt it to see if it's the problem. Am I wrong? I'm remembering that you said it was sputtering & had to feather the fuel to get speed. That could very well indicate the cat.

[Camino LS6]

Clogged cat will show it's self at high speed & with a hot cat. unbolt it to see if it's the problem. Am I wrong? I'm remembering that you said it was sputtering & had to feather the fuel to get speed. That could very well indicate the cat.

Cat and Y-pipe are a single unit (expensive), so I can't just unbolt the cat. I tried to unbolt the O2 sensor, but that's not budging. If I could have gotten it out, any serious change in the way it runs would indicate cat.

Oh, and we can discount the temp sensor (I tried a spare leftover from Mothertruck).

[67impss]

Then I would cut the cat off if it's good you can always reattach with a stainless steel band clamp since you're doing the cat back. If the cat is plugged it will pressurize and relieve its self during valve overlap thus causing the sputtering let alone the inability to keep running at a load.

[Camino LS6]

Hmmm.

[SAmadei]

Just for testing, I would undo the Y pipe at the headers to allow the pressure out and see if it can run the RPMs up to the expected redline.

[Camino LS6]

Just for testing, I would undo the Y pipe at the headers to allow the pressure out and see if it can run the RPMs up to the expected redline.

That would be a noise I'd have to explain later...

At any rate, I can take the engine to any RPM I want right now - I'd just have to do it slowly,

I hate borrowing tools, but I borrowed both a fuel pressure tester and a compression tester, along with an O2 socket today.

I WILL get answers.

[Camino LS6]

Fuel pressure test rules out the fuel pump - had between 11.4 and 12.2 PSI all the time (spec is 9-13 PSI).

Did the "pinch-off" test on the return line again - confirms my earlier test ruling-out the fuel pressure regulator.

[Camino LS6]

Compression test checks out too - all 8 within a few PSI of 150.

But, I found 3 plugs that were fuel-fouled.

[67impss]

No codes thrown by the Puter? maybe a leaking injector

Kinda pulling it out my a$$ rt now but you said you had downer parts rt.

[Camino LS6]

No SES light.

I'm thinking that this goes a long way toward fingering the cat. The problem is that I can't get the damn O2 sensor loose to test that idea. The other possibility is the MAP sensor, which I believe is the same as the one on Mothertruck, so I'm going to swap that in and try it.

If that doesn't change things, it's time to hack the cat out of there.