Speakin of "running rough"...

[Paul Workman]

Regarding my miss/low compression issue, I was pretty certain I was dealing with a mechanical problem on my #8; a bent valve or broken valve spring, or ingested a screw or something? But, I'm just a patient - not a doctor of LT5s. So, since I work only about 10 minutes from Marc H's shop (eat your hearts out!) I ran 'er by Dr. Hiabeck's office for a visit.

I was pretty much resigned to an engine pull, and initially intended to inquire about going ahead with a 368 upgrade, as long as I was going to pull the LT5 and be "in there" anyway. But, I was surprised when Marc told me he was not at all sure it was a mechanical problem - could very well be - but(!) possibly the miss and even the low compression symptom could (over time) well have it's roots elswhere: injectors, coil, plug wire, or even the ECM. So! I've got a laundry list of things to eliminate before succumbing to an engine pull.

If it comes to that - an engine pull that is - I'm gonna give the 368 option a hard look-see! So, in the mean time, I'll be shopping for parts; pistons that will work on stock rods (this, according to Marc, has been done successfully at SGC), sleeves, rings, bearings, cam bolts, etc. And, if it comes to that, I'm hoping I can draw on the rich experience and talent that cruises this board. (Wouldn't even think about it, otherwise!).

All comments and suggestions = very welcome.

P.

[ZZZZZR1]

Paul,

368? All I can say is VERY COOL!


Do it!

Hope you find that issue soon, so you can enjoy that beast!


Cheers

David

[Paul Workman]

Well, so far...

Plug wires: swapped #8 with #5 (same length)

Coil: swapped places w/ the front two (the #7-6 coil now serving 8-5, if memory serves)

Injectors: swapped places; #8's injectors now in the #4 spot.

I shoulda checked resistance of the (Multitech!) injectors before pulling the plenum (and messing up a gasket). But! I have a used set of gaskets (some of Jerry's are on order) to slap on there long enough to heat the engine up and then test the injectors, AND swap ECMs too, if need be.

So! The question is, which cylinder is going to miss now? If it is #5, it is a bad plug wire. If it is #4 - the injectors. If either #7 or #6 fails - the coil comes under suspicion (plugs were eliminated earlier).

If it is a combo......I don't wanna go there yet. Course if there is no change at all, and the (hot) injector resistance checks out, that leaves the ECM. Then, if nothing comes of all this, I guess an engine pull is on the plate to see what's what with the mechanicals.

Sound like a plan?

P.

[XfireZ51]

How about if you just bring the car up here and let's throw a scantool on it. I really doubt it's an ECM.

[ALZR1]

Originally Posted by Paul Workman

Well, so far...

Plug wires: swapped #8 with #5 (same length)

Coil: swapped places w/ the front two (the #7-6 coil now serving 8-5, if memory serves)

Injectors: swapped places; #8's injectors now in the #4 spot.

I shoulda checked resistance of the (Multitech!) injectors before pulling the plenum (and messing up a gasket). But! I have a used set of gaskets (some of Jerry's are on order) to slap on there long enough to heat the engine up and then test the injectors, AND swap ECMs too, if need be.

So! The question is, which cylinder is going to miss now? If it is #5, it is a bad plug wire. If it is #4 - the injectors. If either #7 or #6 fails - the coil comes under suspicion (plugs were eliminated earlier).

If it is a combo......I don't wanna go there yet. Course if there is no change at all, and the (hot) injector resistance checks out, that leaves the ECM. Then, if nothing comes of all this, I guess an engine pull is on the plate to see what's what with the mechanicals.

Sound like a plan?

P.

Forget all questions above,and ask where is all that compression pressure
going.When I checked your compression it was less than 60 PSI and your leak down was at 80% .This is your problem,and it has to do with your pistons,rings,or valves nothing more.



AL.

[A26B]

Originally Posted by ALZR1

Forget all questions above,and ask where is all that compression pressure
going.When I checked your compression it was less than 60 PSI and your leak down was at 80% .This is your problem,and it has to do with your pistons,rings,or valves nothing more.

AL.

Might the list also include the head gasket? Was compression rechecked with a squirt of oil in the cylinder? Could help in determining whether or not valve problem.

[ALZR1]

Originally Posted by A26B

Might the list also include the head gasket?

If it was the head gasket you would either have A cooling issue,or
an adjacent cylinder down on pressure as well or both on an LT5 Motor.
Paul's motor doesn't have any of these problems
Paul also had checked the rest of the cylinders and said that they were about
180 PSI.


AL.

[A26B]

Originally Posted by ALZR1

If it was the head gasket you would either have A cooling issue,or
an adjacent cylinder down on pressure as well or both on an LT5 Motor.
Paul's motor doesn't have any of these problems
Paul also had checked the rest of the cylinders and said that they were about
180 PSI.

AL.

Please explain why the LT5 head gasket failure would necessarily affect the adjacent cylinder. Each cylinder has an individual copper seal. LT5's are prone to head gasket failure at about 7:00 position, into the coolant area.

Granted, a head gasket, fully blown, would cause (1)temp issues, and at the very least, (2)areation in the coolant, both of which should be readily detectable.

I'm not saying it IS a head gasket, just that it might also be a possibility since head gaskets have a greater incidence of failure in the LT5 than valves or piston/rings, under normal conditions. The other less frequent possibility is for a secondary butterfly shaft screw gets ingested.

[ALZR1]

Originally Posted by A26B

Please explain why the LT5 head gasket failure would necessarily affect the adjacent cylinder. Each cylinder has an individual copper seal. LT5's are prone to head gasket failure at about 7:00 position, into the coolant area.

Granted, a head gasket, fully blown, would cause (1)temp issues, and at the very least, (2)areation in the coolant, both of which should be readily detectable.

I'm not saying it IS a head gasket, just that it might also be a possibility since head gaskets have a greater incidence of failure in the LT5 than valves or piston/rings, under normal conditions. The other less frequent possibility is for a secondary butterfly shaft screw gets ingested.

You're not suggesting that copper is indestructible are you?


AL.

[A26B]

Originally Posted by ALZR1

You're not suggesting that copper is indestructible are you?

AL.

Of course not.