Dyno Results

[WICKED LT1]

After a little trip to the 'ol chassis dyno....


262.0 RWHP and 315.3 RWTQ

Not bad, but there was a strange drop-off at 4200 rpm that we can't explain. It peaks out at about 4200, then falls on it's @ss till redline. It dumps like 50hp in that span. So we think we need to look into the PCM and the ignition and make sure everything is ok.

So I'm back to the garage and hopefully some answers. I'll post the findings.

-Paul

[N20LT4Bird]

Yea, you should be making power to at least 5500 on a stock setup. Somethings not right? Did you get O2 readings with the dyno? What were the m.v.'s doing at that RPM?

[WICKED LT1]

No I didn't get O2 numbers. These were just base runs. Their wideband also requires a larger bung on the pipes that I do not have. If I do this often I might get one though. The cable I need is on order from AKM, and after I out some basic ignition stuff on her, I'll take it back with the data logger.

A question though, what would you do if say someone tossed a HPP tune on the PCM and didn't put the stock tune back before they sold the car? How would you tell? Something the guys said at the shop makes me wonder. Hos first question on seeing my little oddity was if it was Hyperteched..... From the conversation this guy appears to have some tuning experiance and got me thinking..... Any thoughts?


-Paul

[Rob]

I doubt it would be a Hypertech problem. Possibly the opti going bad, plug wires, plugs, running real lean, clogged fuel filter. Could be any number of things.

Need to put a scan tool on there. Then you should be able to narrow it down.

Rob

[Al 96 Ram Air T/A]

Miles?

How many miles you got on your engine? It could be mechanical as well. Weak springs or collapsing lifters will do the same thing. If you have a lot of mileage on your heads, this is not uncommon. Or, if you have "upgraded" heads with upgraded springs, it could be collapsing the hydraulic lifters. I doubt programing would cause this. It sounds a bit like "valve float".

If it's mechanical, sounds to me to be electrical (i.e. Opti, plug, and/or wires) or fuel flow problems. Have you checked your fuel system for clogged fuel filter, worn pump, etc? Your O2 readings can shed some light on this, especially if she's leaning out. I know at high rpm's, I'm putting out a small amount of black smoke, telling me she's running rich. But, I prefer to be on the safe side than have a few extra ponies running lean. Your making gobs of torque but your horsepower is a bit low. I pulled 280 hp and 310 ft-lbs with a similar set up. I was making about 260 RWHP at 4200 rpm as well, but continued to build, peaking at 5500 rpm.

Your fuel filter and the intake tract is not clogged, right?

[WICKED LT1]

Re: Miles?

Originally posted by Al 96 Ram Air T/A
How many miles you got on your engine? It could be mechanical as well. Weak springs or collapsing lifters will do the same thing. If you have a lot of mileage on your heads, this is not uncommon. Or, if you have "upgraded" heads with upgraded springs, it could be collapsing the hydraulic lifters. I doubt programing would cause this. It sounds a bit like "valve float".

If it's mechanical, sounds to me to be electrical (i.e. Opti, plug, and/or wires) or fuel flow problems. Have you checked your fuel system for clogged fuel filter, worn pump, etc? Your O2 readings can shed some light on this, especially if she's leaning out. I know at high rpm's, I'm putting out a small amount of black smoke, telling me she's running rich. But, I prefer to be on the safe side than have a few extra ponies running lean. Your making gobs of torque but your horsepower is a bit low. I pulled 280 hp and 310 ft-lbs with a similar set up. I was making about 260 RWHP at 4200 rpm as well, but continued to build, peaking at 5500 rpm.


There are 64K on the car right now. I am just starting to chase this, and a few easy things are on the list first. I am going to replace all the plugs, wires, and other misc ignition and run a scan and a fuel pressure test as well. If I can manage I might try a leakdown, but it's a real PITA on these cars. I am going to go on faith that the opti is ok for now, because it runs and idles like a dream on the street, so I have to go with the easy stuff first. This is one of those things that only becomes evident on a dyno, or the track and I'm not unhappy with the results. At least I have a real good set of leads to chase. Both the dyno guy and myself expected about 285hp or so if the motor would have kept pulling. The graph is like a straight beeline for 300 until it hits that dip, so those numbers look right. Thanks


-Paul
Your fuel filter and the intake tract is not clogged, right?

[markd79ta]

Re: Miles?

Originally posted by Al 96 Ram Air T/A
How many miles you got on your engine? It could be mechanical as well. Weak springs or collapsing lifters will do the same thing. If you have a lot of mileage on your heads, this is not uncommon. Or, if you have "upgraded" heads with upgraded springs, it could be collapsing the hydraulic lifters. I doubt programing would cause this. It sounds a bit like "valve float".

When I read your post, this was my first thought. It sounds like you are getting some valve float. I would check your fuel pressure to see if you are getting any drop off, as well as looking at ignition, but don't rule out the valve springs. Has the motor been revved at 6,000 or higher a lot?

[WICKED LT1]

Some testing results and q's

Well, thanks to Fred for the outstanding 4th gen scanner doc, that let me to a TTS Datamaster, and to Andrew over at AKM who is a godsend w/ the cables!!!

That said, it appears that my power falloff is a direct result of knock retard. At approx the same rpm over multiple runs I get about 10deg of knock retard that saps the power right out. My O2's are both somewhere around 950mv when this happens so I have ot believe that I;ve got a lean condition that is causing some spark knock.

What I wonder about is that the PCM seems to be very liberal with the advance curve, and it is giving about 41deg advance when it gets to this point. Man, that seems high for a GM sb. Can anyone tell me if this is right?

So, for a small list of questions,

Max spark advance?
Max knock retard?
Is it normal to get a little knock retard on lt1s w/ similar mods?

And lastly, does anyone have an idea on how to tell if the PCM tune was altered? Easier that buying another PCM? Maybe an .lt1 file to compare or something.

I am going to put a Fuel Pressure gauge on it later on to verify that it should not be running out of fuel. Thanks

-Paul

[Joe 1320]

Re: Some testing results and q's

Originally posted by WICKED LT1

That said, it appears that my power falloff is a direct result of knock retard. At approx the same rpm over multiple runs I get about 10deg of knock retard that saps the power right out. My O2's are both somewhere around 950mv when this happens so I have ot believe that I;ve got a lean condition that is causing some spark knock.



-Paul

Nope..... 950mv is rich. You are experiencing knock from over rich and most likely some sort of ignition failure. I've seen a condition like this that was related to the coil driver module. When the coil couldn't keep up with the rpms and load/ I was seeing 10º of knock yet the 02s were rich. In my particular case, the coil driver module connector was making intermittant contact. I had to message the pins in the connector to get a tight fit, problem solved. Not sure if that is the exact problem, but you are definately running rich.

[Al 96 Ram Air T/A]

Injectors

Now that you know your rich, it could even be an injector problem. Poor atomization or a stuck injector could cause excess fuel to leak into the cylinders causing poor combustion/rich condition.

[JL8Jeff]

On my old 93 Z28 Indy Pace Car, I was seeing O2 readings in the high 900's and low 1000's under WOT with a Powerdyne supercharger and SLP computer chip. No lack of power and no falloff at the top end. But I was also only seeing 2 degrees of knock retard under boost on a very humid 95 degree day. I think I saw at least 38 degrees of advance, but my memory is getting shaky so I can't say that's 100% correct. You may be getting some rocker arm noise that is causing the knock sensor to pull the timing. You may want to try the LT4 knock module to see if that cures your issues. One of the guys in our club was seeing 12-16 degrees of retard on his 95 and I don't think they ever figured out what the problem was. I'll ask him tonight if he shows up at our meeting.

[WICKED LT1]

Re: Re: Some testing results and q's

Originally posted by Joe 1320
Nope..... 950mv is rich. You are experiencing knock from over rich and most likely some sort of ignition failure. I've seen a condition like this that was related to the coil driver module. When the coil couldn't keep up with the rpms and load/ I was seeing 10º of knock yet the 02s were rich. In my particular case, the coil driver module connector was making intermittant contact. I had to message the pins in the connector to get a tight fit, problem solved. Not sure if that is the exact problem, but you are definately running rich.

Thanks Joe. It has been so long since I have done some of this stuff, that I'm finding that I'm a little rusty. I am going to toss some plugs and wires at it, and then check on the opti cables and such. I do notice some black smoke when I throttle it real hard, but I have never seen that make something knock like this. I am with you on the ignition bit though, I think that is certainly step 2 right after the FP test. Thanks man.


-Paul