Need help understanding scan data

[QB93Z]

The last time I was at the drag strip I thought my 1993 ZR-1's performance was lower than usual. I had slower ET's and lower top speed.

A scan I ran during one pass showed 1 instance of knock spark retard which I have seen before.

But the scan also showed Injector Duty Cycle of way over 100%.

Thinking that I may have a fuel supply problem, I changed the fuel filter and tested the fuel pumps using the FSM. Both fuel pumps appear to be working properly. I get 49 psi, steady at WOT.

I recorded another scan yesterday after the fuel filter change. Here is a portion of the scan during a hard acceleration to 100 mph:



Am I right in my understanding that INJ DC being high means the computer is making the injector pulse width longer in order to get enough fuel to the cylinder?

Any ideas on where to look next?

Jim

[tpepmeie]

Datamaster does not correctly apply the pulsewidth scalar when the 2ndary's are active. Your real DC is approx half of what is shown.

[Paul Workman]

I compared your data to one of my WOT scans with the 90 Z, and with one from my former LT1 Vette.

What jumps out at me is your injector dwell time on one (right) side, and the O2 readings on that same side:

The PW is nuts on the one (right?) side. However, the O2 reading likewise indicates very rich, so the sensor appears to be working. (The pros here that look at this stuff almost daily...please step in.) So, I would be wanting to eliminate a connection problem between the O2 and the ECM first. I'd like to hear what Jeffvette or some other turners think. (I'm subscribed on this one!)

P.

[tpepmeie]

Originally Posted by Paul Workman

The PW is nuts on the one (right?) side.

P.

No, the PW are fine, 23.59 ms each side. The numbers you are citing (16.9/49.6ms) are also normal.

Todd

[Aurora40]

From what I understand (from Todd), you basically divide the duty cycle/puslewidths in half when the secondaries are operating. Datamaster isn't doing that.

Edit: The only thing sorta off is the MAP pressure? Seems sorta low, especially if the ambient pressure was over 100kPa that day. If you scroll back to when you were at WOT but at a low RPM, what is the pressure there? How much is it dropping as the RPMs rise? I usually see about a 2-3kPa drop or so. More than that, and perhaps your air filter is dirty or your duct is collapsing or something like that?

[QB93Z]

Thanks for the responses.

I understand now about the Injector duty cycle reading, divide by two. I went back to some older scans and the readings were similar to yesterdays, but I never noticed the X2 value before. I guess I was concentrating on other readings.

Bob, I looked at some other WOT data on this scan (long pull from 40 to 70 mph in fifth gear, 1700 to 2800 rpm. MAP flucuates from 99.3 to 100.1 for the 5 seconds duration (avg 99.7). During the 0 to 100 mph run pictured above, the MAP flucuates from about 97.5 to 98.2 KPa ( avg 97.85). Is the difference you are pointing out?

I will check out the duct and the air filter. Thanks.

Jim

[Aurora40]

Hey Jim,

What I meant is, look at the MAP at low RPM at WOT. What is the highest the MAP reading goes up to? That is potentially the atmospheric pressure at that time. It's better if the RPM is really low, but at the dragstrip you probably aren't driving that way.

If the max pressure is that 100.1kPa, and in the snapshot it is 96.7kPa, then you are getting about a 3.5kPa pressure drop. That seems a little bit high, though not a lot. I think I usually have closer to a 2kPa drop as the revs climb. Possibly it gets lower as the RPMs go up from there? That snapshot is at 6,300.

Intake pressure directly affects power. Though here we're talking maybe 2% at the max, which on a 400hp motor would be like 8hp. Certainly that's not nothing but hardly huge. How "off" were your runs?

[XfireZ51]

Benchmark the MAP sensor first before attempting to compare WOT. When datalogging, I first record all sensors with ignition ON but motor OFF. That will give you MAP reading at atmosphere. Its not always 100kPa. MAP will fluctuate at WOT and be at its highest point at torque peak, for instance, 5300-5500rpm for my motor.

[Aurora40]

Why would the MAP be at it's highest point at peak torque?

[flyin ryan]

Peak TQ. is always the most volumetric efficent point.