L67 Too much Retard

[Imp558]

A friend of mine has an L67 kit car, everything is new and it's on it's second engine. Both engines were weak and we ran the gauntlet diagnosing. Now we can see 20 - 30* of retard with no apparant cause. It's running 93, good fuel pressure and all and I don't know where else to look.

No codes, 2 Ckp's, hell - 2 engines exactly the same. No sensors were brought from the first engine.

I feel it has to be a problem with the vehicle, it's got stock engine mounts but maybe excess vibration being misinterpreted by the KS's?

[White93z34]

What transmission? what modifications to the engine?

[Imp558]

Bone stock everything, the 4T65e HD is native to the engine. IAT is 100*F, CTS is 194* F. I brought the fan temps down to 205* and then he put a mondo radiator on it. The PCM is a completely stock tune with no emissions, cooler fan, stock revs, no VATS. No table modification whatsoever. Stock airbox, stock exhaust with a muffler a couple feet from the DP.

[vipmiller803]

I have heard of vibrations causing false kr, but only with solid mounted engines. Does the engine hit anywhere it shouldn't? Did you data log to see the timing or was it with a light? Any spare ecu's you could put in?

[Imp558]

It's on it's second ecu and engine. Stock mounts.

[Imp558]

It's on it's second ecu and engine. Stock mounts. I'll have to see how the exhaust is suspended.

[Schurkey]

How much retard is being commanded by the ECU?

 

Is this thing running on "Limp Home" mode?

 

First Guess:  All your answers are in the data stream.

[digitaloutsider]

Are you absolutely positive the PCM doesn't have the L36 calibration or something? What year PCM?

[Imp558]

It was all out of a 1998 PAU, same cal, just did the basics. He has the car in another city so I can't actually see it.

[Imp558]

I'm thinking the exhaust is either hard mounted or hanging off the DP and wagging like a Dog's tail. There really isn't any other option. The first engine was an L36, it was weak so we did the L67, now it's weak and it's too far away for me to actually get my HPT tool on.

[digitaloutsider]

You would need to have some SEVERE vibrations to be seeing false knock that high. False knock is generally seen in a log as a weird spike/artifact. Not continual, sustained knock.

 

Getting a log would really be the best way to rule stuff out. Where in the powerband does it start showing this much knock? Everywhere?

[Imp558]

I can't get to it, he's going to have to get a log and send it. It's weak everywhere, right off the line. I'm picturing vibration from the exhaust traveling back and making KS Bank 2 all kind of pissed.

[Galaxie500XL]

You said in your first post it’s a kit car...what sort of kit? I’m wondering just how solid the mounts, and associated welded sections are...I might be way off base, but when the obvious isn’t helping, sometimes it’s the oddball stuff that’s the problem.

[digitaloutsider]

I thought about this some more, and when you say it's a kit, do you mean like a tube chassis? Since I'm out of any better ideas, could it be weird some harmonics that's getting passed through the chassis of the car and into the engine? Like Galaxie says, maybe with mounts that are too firm it's all too much? 

 

Still don't have any other good ideas to look at. Maybe backprobe the knock sensors to the PCM and make sure there isn't a short in there or it's getting grounded against something when the engine moves?

[Imp558]

two engines, two different harnesses. The first was a SI 3800 and this one's an L67. It needs the knock sensors monitored and I bet KS bank 2 is flipping shit over the exhaust being mounted in a funny way. I just wish I could get to it and put my hands on it for 15 minutes. If it's not exhaust your assumption is really the only other explanation.