I just got Datamaster working on a 1994 Firebird six-speed. When I got the car it had been scanned and I replaced the spark plugs, spark plug wires, vapor cannister purge solenoid, fuel filter.

Here is a Datamaster file from a cold start engine idleing with blips of the throttle. It had a MAF code because I had unplugged the MAF with the engine running a few days ago.

9-16-07 first idle.uni

I cleared the code and we drove the car to town, the road is gravel so we didn't drive too fast.

9-16-07 third trip to town.uni

Everything was fine so we drove the highway to Bismarck.

9-16-07 4 trip to town.uni

The SES light came on so when I picked up my wife again she drove it.

9-16-07 5 trouble code.uni

The code was EGR failure, the SES light came on in cruise going uphill in sixth gear about 60-65 mph.

It did that one more time on the way home the same way kind of lugging it uphill in sixth.

So the only code seems to be the EGR failure but according to the logs the EGR does work, maybe something is sticky.

It seems to run good except around 2000 light throttle, there seems to be a miss. If I had the LM-1 wide band on it I could tell more but I wonder if it is an ignition miss since the car has an untouched opti on it and 69,000 miles. I think the car is completely stock except for a TB coolant bypass, 160 thermostat, gutted cat, and a ram air conversion. I'm pretty sure it has never been tuned.

Is the O2 MV supposed to move around during cruise as much as they do?

I wanted to be able to reset the SIR codes with Datamaster but it doesn't look like it can do it. Is the dealer the only option for that?

Any comments?

 

What in the log tells you the EGR is working? It will show you the EGR duty cycle, but that is just what the PCM is setting the duty cycle at. There is no feedback to tell you the EGR valve is actually working, or that there is EGR flow. To test the EGR system, the PCM cycles the EGR valve, and looks for a slight change in MAP pressure. It can only do the test when the engine is under a very steady load for an extended number of seconds. That's why is runs the test at cruise conditions..... when you aren't fiddling with the throttle. If the vacuum lines are leaking, the valve is not working or the passages in the intake are plugged with carbon, you won't get enough EGR flow. You can even set the code with a very low backpressure exhaust system.

When the PCM is in closed loop, the O2 sensor mV should be swinging rapidly (changing almost 10 times per second) over the full range of 0xx - 9xx mVolts. If it isn't doing that, there's something wrong, or you have exceeded the theshhold of throttle position vs. RPM and the PCM has gone to power enrichment (PE) mode and is no longer using the feedback from the O2 sensors to set the pulse widths.

DataMaster reads the PCM... that's all. SIR, EBCM, etc do not interface with the PCM. You need a premium level scanner to access those systems.

 

I see how the EGR works now. Can you see the MAP change on the datamaster log?

Thanks,
Jesse

 

The EGR valve vacuum canister diaphram leaked bad when I tried to pull a vacuum on it. I can't see how it was opening at all. It was leaking through when closed which was affecting the idle. So I got a new one on order.

Thanks,

Jesse

 

Follow up after a new EGR valve and solenoid were installed;



The manifold pressure follows the EGR, exactly the way it should.

The car runs better too, the EGR was leaking through which affected low RPM and idle performance and at 60-70 MPH cruise it was tripping code 32.

It's getting there.

 

It also idles "leaner" on the datamaster histogram, I'd guess this is because the O2s see more O2 when the EGR is not leaking though.

Should weld a bung in and check it with my LM-1.

Can't wait to see what the working EGR does for gas mileage, it made about 23 @ 80MPH with the non-functional EGR valve.

 

There was an idle problem, missing and sometimes backfiring when you crack the throttle off idle that the new EGR didn't cure. Part of the idle problem was that the MAF housing was cracked.

LT1 MAF crack.


I put a new MAF on and it is much crisper during a rap of the throttle. Datamaster shows more airflow during these throttle blips, the missing and sometimes backfiring is completely gone. It's as it the cracked MAF was measuring airflow as too low resulting in a lean miss.

I got the new MAF on e-Bay is is supposedly a genuine GM MAF but it does not have the AC symbol on the plastic housing and did not come in a GM or AC box.

3.5" LS1 MAF Sensor - BRAND NEW! - 3 1/2" Mass Air Flow

This information might help someone sometime.

 

Somebody is reading this thread, I didn't look at it 200 times.

The car had a road trip yesterday with the new MAF. It runs WAY better.

The new MAF is reading the airflow much higher than the old MAF, so the engine is running richer.

The 3 gear WOT runs 1500-5000 RPM bear this out;

Before new MAF at 5000 WOT;

injector DC 59/60
airflow 140

peak datamaster dyno HP 238

After new MAF at 5000 WOT;

injector DC 97/95
airflow 220

peak datamaster dyno HP 249

The injectors at 97/95 is obviously quite high, there might be a fuel pressure problem. I have put a new fuel filter on the car but didn't want to change the pump if I could help it. I haven't checked the fuel pressure, been wondering where to get good gages to do that.

The LTerm Counts and STerm counts dropped quite a bit, the datamaster histogram shows some pretty red cells in the cruise areas and green in the higher RPM WOT pull area. I don't know what this means - yet. Gotta apply my brain to this - or a bung to the exhaust pipe for my LM-1. (I can't believe I forgot that when I had the y pipe off.)

I could post the before/after MAF files if any are interested in looking at them.

 

The injector duty cycle calculated in DataMaster appears to be too high... the calculation method appears to be correct, but the results don't make any sense. No way an engine running at stock HP would max out a stock injector.

Most auto parts stores will carry a "fuel pressure test gauge" for about $40. It has the correct -4AN fitting to attach to the Schrader valve, a pin in the fitting to open the valve core, a long rubber hose to the gauge, and a little pushbutton bleeder valve to release the fuel pressure. To use it at WOT, you need to tape it to the windshield.

The alternative would be an AutoMeter electronic fuel pressure gauge for the dash.... always handy to have, but a bit pricier at close to $200. I have one mounted in the center A/C vents, along with a nitrous pressure gauge and an oil pressure gauge. You have to use an electronic gauge if its inside the passenger compartment. Based on personal experience, the high pressure isolators that allow you to mount a mechanical gauge inside are simply not reliable.

I don't understand why you feel the higher (more accurate) air flow value is causing your engine to run richer. If "indicated" air flow increased, the the long term corrections should have dropped, meaning the A/F ratio is still being controlled at stoichiometric in closed loop.

 

Are you the author of this page?

http://members.aol.com/InjuneerZZ/Sc....htm#step%2019

If so it is the best information I have found so far but it will take some time for it to sink in.

I'm totally new to fuel injection tuning, that might be a surprise with me owning an engine dyno and all, but all I have done is carb tuning. I haven't even owned a fuel injected vehicle until the last couple years, and this Firebird is the first one I've run any kind of scanning software on. So I'm floundering a bit here.

It's pretty dumb for me not to be running LM-1 logs on these changes since I have an LM-1/auxbox setup I use with my engine dyno. The LM-1 is something I do have experience with and do know how to use, plus the information from it is awesome. Hmmm, I'll bet I could log fuel pressure with the Innovate auxbox. Hey!!

Can't log with the LM-1 and datamaster at the same time though unless I get both laptops in the car, heh. That will be fun, running two laptops while driving, ha ha, just kidding.

The reason I think the engine is running richer is that the missing/backfiring is gone. The missing/backfiring was mild, and very similar to a carburator accelerator pump shot that is too small. In addition, in cruise, the car had a slight shuddering, exactly like carb jets that are a little lean, this totally dissapeared with the new MAF. The car is noticably smoother in cruise now, even my wife commented on that fact. So I'm pretty sure the running a/f ratio changed somehow, it seems to me the increase in the injector pulsewith indicates that. I don't know yet how to reconcile this with the STerm counts, and the LTerm counts, I don't understand what they mean. It sure seems to me that the airflow @ 140 with the cracked MAF would make the engine run leaner than it would with the airflow @ 220 with the new MAF.

One thing that might be notable is the EGR and especially the new MAF are pretty big changes, I did not reset the PCM by killing its power. That and the fact these changes have taken place in the last 200 miles or so might mean the PCM hasn't learned enough yet. Maybe I should reset the PCM, I don't know.

Here are the before/after new MAF datamaster files;

10-2-07 4 trip to town after egr fix.uni 314K

10-9-07 2 trip to town after MAF.uni 247K

The only change was the new MAF.

 

The second one won't open.

 

I think it will now.

 

On Oct. 27 we ran the car with both the LM-1 and Datamaster logging. Had some problems with the LM-1 the RPM input is very sensitive and didn't log a clean signal, and the vacuum channel went flat during the hiway runs. This means there isn't a good reference to what the engine was doing as RPM and vacuum are very good clues as to engine load. Next time I will get the vacuum signal from the fuel pressure regulator. I could configure the LM-1 auxbox to log TPS. I'll get it all working for next time. The fuel pressure log worked very well when I finally got the channel setup figured out.

The A/F ratio pretty much ran 14.5- 14.6 except during fuel enrichment mode, it ran about 12 then.

Idle fuel pressure 33
Idle fuel pressure with vacuum hose off regulator 43.5

Cruise fuel pressure 33-35
WOT fuel pressure around 42

I wanted to see if any injectors were leaking so I logged fuel pressure when the engine was shut off.

Fuel pressure at idle before shutdown 34
Fuel pressure at engine shutdown 26
Fuel pressure 1.5 seconds later 29
Fuel pressure 23 minutes later 40

I planned to post LM-1 logs but with the vacuum and RPM messed up they would be too confusing.

We took the car on a 600 mile trip this weekend, on the main hiway leg it made 24.7 MPG, this is with an overnight stop, quite a few road changes involving maximum performance takeoffs. The worst it has ever made is about 19 MPG, that would be short trips of 100 miles including about 15-20 miles of town driving.