SS RRR

iTrader: (2)

No codes I take it? If all else has been checked then try a new chain and see what happens.

Both the LT4 and EDLT4 timing chains are true rollers. There's nothing about a roller chain that causes problems with a knock sensor.

Burnt plug wires won't cause a backfire problem.

koolaid_kid

iTrader: (21)

Let's see, yes, MSD 8.5 wires. No perceivable arcing seen or heard.
Where is the PCM ground? I checked the ones on the front driver's side, but it seems the PCM would be grounded on the passenger's side rear.
I was pretty careful with both Optis when I had them apart. Accidents will happen, of course, but everything was keyed as I recall.
The 3146 is a double roller, which has clearance issues with an LT1 cover according to various posts. But I have a Dremel and I'm not afraid to use it.
Speaking of that, Summit lists 6 3146 derivatives, from $80 to $174. Which one is the correct one?
I find myself in parts replacement mode, which I despise, but I really wanna get this damm car going again.

AChotrod

iTrader: (17)

Its on the passenger side of the block up near the top under the two rear plugs. Not possitive but its conected to that metal bracket right under the heads
I broke mine doing my engine swap so I know its possible and easy to break off.

Also check the grounds near the coil/icm maybe they are corroded or broken loose.

koolaid_kid

iTrader: (21)

O.K., I'll check the passenger's side. I remember bolting that back in during the engine installation, but who knows. I was reaching in there while changing the plugs and verifying the plug wires and I could have knocked it loose.
I checked the grounds at the coil/ICM yesterday. All very solid, no corrosion.

I appreciate all the suggestions.

AChotrod

iTrader: (17)

Mine broke putting it back in damn o-ring just snapped

ulakovic22

iTrader: (12)

Why not?

SS RRR

iTrader: (2)

Because a backfire is the early or late ignition of fuel. How can a burnt plug wire be responsible for that?

Puck

iTrader: (17)

3145 cloyes double roller works with LTXs, you just need to use an EWP.

You can only use a single roller with the stock waterpump.

slingshot928

Maybe the timing jumped with the chain being loose, but it would have probably detonated right after it hit 6500...when you put the new opti on..is it aligned properly in the cam.

koolaid_kid

iTrader: (21)

Burnt wires could cause it if:
Two wires which touch each other both lost their insulation
Each remained firing
Each jumped across to the other, firing each plug twice.
Seems like a reach, but I am certainly reaching at this point. Wires have been checked, however.
I have an EWP, so I can go double roller. I'm just confused over the 3145/3146 thing. How can both work with our engines? And why does Cloyes make so many versions of each?
I thought the timing may have jumped since I checked out electric/electronics and fueling first. However, when I pulled the timing cover and aligned the dots, the cam is still in time.

And no codes, that would have been too easy.

SS RRR

iTrader: (2)

It is a reach. Too many circumstances would need to take place for spark to jump from one wire to another. With these engines the only way insulation is damaged is when it gets burnt. The wires are segregated enough in the areas to where they are most likely to burn.

koolaid_kid

iTrader: (21)

I agree. I don't have headers, and I was very careful to route the wires in the stock locations, plus I double checked them during this investigation.
To sum up:
1) If two completely different Optis yield the same results, it is probably not the Opti.
2) If fuel pressure is good, the injectors are not leaking and the plugs are wet, it is probably getting fuel.
3) If the plugs are new, as the wires, they are probably O.K.
4) If two different ICMs and coils were used with the same results, it is probably not that.
5) I loaded a different tune into the PCM, no change.
6) The cam is in time, visually inspected.
7) No odd mechanical noises detected. Removed d/s valve cover and verified all rockers functioning correctly. (Engine has full r/r, LS7 lifters and chromoly pushrods, just checking my work.)

I guess I could have adjusted the rockers incorrectly, but it seems that would have shown up immediately, plus some would have been noisy, which they are not. I could have some too tight and none too loose? Again, seems like another reach.

SS RRR

iTrader: (2)

If the rockers aren't adjusted right then you could have damaged the valves. You should also do a compression test.

ulakovic22

iTrader: (12)

A backfire is ignition outside the chamber, either intake or exhaust. For this to happen you have to have an unburnt mixture enter either the intake or exhaust. There are only a few ways that you can have an incomplete burn, too much fuel, not enough air, weak spark, or as you indicated too early/late of a spark as the mixture is coming or going and the valves on either side are still open. If you have a burnt wire you will have a weak or no spark that will cause a raw mixture to enter a hot primary tube and possibly fire on it's way out.

I'm not saying that this is his problem, but I'm offering up ideas for things he should check to make sure they aren't. A backfire when letting off the gas after making a WOT pull isn't unheard of because the engine is normally running a little on the rich side when at WOT. Depending on the situation if the complete mixture isn't burned on it's way out as you are decelerating it will backfire.

Have you checked to make sure your header gaskets are still good and aren't leaking? If your O2's are reading a lean mixture because of a leak it will dump fuel and cause your plugs to be wet and foul. Have you checked your O2's voltage/response?

koolaid_kid

iTrader: (21)

I agree. Even my sport bikes do this, and I am not concerned. I'll check the exhaust manifold bolts this weekend (no headers, rear mount turbo). I'll see if I can get to the O2 sensors and visually inspect them. It is possible they are fouled. Can't really check the response until it runs. They were fine the last time I ran a data log, but at this point all bets are off.

SS RRR

iTrader: (2)

Have you ever experienced a backfire problem with a burnt plug wire or is this just an opinion through your reasoning?
I've had everything from mildly burnt to almost charred in half plug wires before and have never had a problem like what you are trying to explain. Hesitation under load, yes. Spark jumping from wire to a ground, yes, but never a backfire.

ulakovic22

iTrader: (12)

It sucks when it comes down to parts swapping. Have you pulled both VC's or just the one to verify valves/springs are all opening and closing? Have you checked IAT and MAF sensors to make sure they are reading correctly? If they aren't reading the right amount of air and it's temp entering the engine it would cause problems. Obviously there is still the timing chain to replace. If you can get an oversized crank gear from Thunder Racing, it's tighter than **** going on, but helps a lot with slack in the chain after it wears in.

ulakovic22

iTrader: (12)

Since it's never happened to you it's just not possible?

I'm obviously not an expert like you, but I have had backfiring issues on my Camaro just before I sold it. I swapped the opti with the one from my truck and it didn't fix the issue. Eventhough the stock plugs/wires looked fine I replaced them and the problem went away. In either case, whether it was bad plugs or bad wires, spark was obviously not firing at one or more cylinders causing my stumble, hesitation and backfiring.

SS RRR

iTrader: (2)

No reason to get all sensitive. These are merely questions. What I am saying is that with the many plug wires I've gone through I've never had a backfiring problem. I have never heard of anyone having a backfiring problem with burnt wires on a LT1 and anyone I've known with a LT1 has never had a backfiring problem due to burnt plug wires. I'll put it this way, there are far more many things to explore other than plug wires causing a backfiring issue. In your case just claiming replacing the plugs "and it went away" is really not enough evidence to say it was just plug wires. You should well know electricity follows its own logic. You read all the time people throw ignition parts at their engines and it helps temporarily and a short time later the same problem arises and they're back to square one.

ulakovic22

iTrader: (12)

I'm not getting sensative, I was merely answering your question. You attack anything that doesn't fit into your logic box. As I said before, "Since it has never happened to you it's not possible?" According to your response, that's what you are saying. Between you and your friends you've never encountered a burnt plug causing a backfire. I've had consistant backfiring issues and replacing the plugs/wires fixed the issue. Take it for what's it's worth, if you don't feel that replacing a part and the problem going away isn't enough evidence for whatever reason, so be it. I'm not going to screw up another thread arguing with you over something as stupid as a plug or plug wire.