Just burned my first couple of proms tonight.
Had to increase the maf high diag error threshold from 45 to 55 to stop a code 33 issue. Looks like it worked!! Haven't actually driven the car yet. Just finished the brakes.

While car was up on stands, I decided to start the eng and shift to drive. Wanted to see if the ecm would register vehicle speed correctly since I'm still using the 82 CFI speed buffer with a L98 eng/ecm. Good news is, it looks like it is reading the speed correctly.

With brakes released and tranny in drive, the wheel speed went to ~50 mph and eng rpm went to 1450 RPM all by itself. I shifted to neutral and let wheels coast down. When the wheels stopped, the eng rpm dropped back down to 900 RPM. Is this normal for a 87 L98??

 

Interesting having to run the diag up like that, many engine mods?.

Running with the wheels with no load may kind of confuse matters since the TPS is so low for a given speed. If the speedo reads about right that's all I'd count on being good info when in gear like that.

That really can be dangerous having the drivetrain spinning at 50 MPH. You'd be amazed at the energy stored in the wheels tires driveshaft if something were to go wrong.

 

Just got back from my first test drive. Car will maintain 40 MPH without me touching the gas. Shift to neutral and slow to a stop. As soon as the car completely stops, the idle drops from 1400 to 900.
Got a code 43 after eng temp reached abt 205 degs while in traffic.(outside temp is 95) Car was real jerky while trying to get going. Pulled over and reset the ECM. Fired it back up and got a code 33. I thought I had gotten rid of that when I increased the maf high diag error threshold from 45 to 55. When I slowed down to enter the neighborhood, the code 43 re-appeared (eng temp was coming back up and reached abt 205). Thinking maybe the ign module is unhappy abt being hot.

Before the codes appeared, in closed loop, BLM were 140 to 150.
Thinking abt decreasing the single and double fire inj sizes from 24 to 23, and also adjusting the maf high diag error threshold to 60.

What do ya think?

Including sig this time so you can see the mods.

 

Code 43 is a knock detection system problem. You may have enough mods to require some major changes in your cal. Up the max MAF malf even more (and maybe time to detect), and look into what the code does to set malf 43.

RBob.

 

I could be wrong, depending on the degree of modifications you've made to your car, but having to raise the MAF diagnostic threshold beyond 55 doesn't sound right to me. Have you checked (or changed) your MAF power and burn-off relays?

I have an 88 Vette with a ZZ4. I did some porting on the TPI plenum and base, bypassed the coolant out of the TB, removed the air pump, put on a free-flowing dual exhaust system and added a higher stall converter. I got intermittent code 33 for a while--but not on the stock PROM. The car had a junk ADS chip in it at the time. I went back to the factory calibration for a while before I started burning my own PROMs and the code 33 went away. On my first few chips I raised the MAF high diagnostic to 53 just for good measure. Since then I've gone back to 45 with no problems.

You might double-check, and/or fiddle-with your TPS and min. idle air adjustments, especially if you're having trouble with the car not wanting to idle-down.

Jason

 

After all the mods, (did all the mods in my sig at the same time) I had to increase the min idle adj quite a bit to keep it running with the IAC closed.
TPS is at .56 volts. From an old post, I saw that pushing the TPS sensor fwd and up while tightening can help code 33 errros. Theory was that the geometry is better like that.

Both MAF pwr and burn-off relays are new. I've checked and double checked wiring..

Gonna try changing the FI size to 23 from 24 and increase the MAF diag from 55 to 60. We'll see what happens..

 

Went for another drive late last night. MAF code 33 came back. Up'ed the threshold to 70, but still got the code 33. Unchecked the MAF diag flag and the code 33 stopped. I can at least get into closed loop now, but only if I'm going 55+.
The code 43 didn't re-appear.

When I let off the gas at abt 60 or so, the inj pulse width goes to 0.0. As car continues to slow down, right at 45 MPH (1000 RPM), the inj PW goes to 2.2 ms and the car jerks. Car will continue to slow a bit more, then level off and cruise at abt 40 MPH without me touching the gas, TPS is reading the same as it normally does at idle (.56V).
If I try to maintain a steady 45 MPH, PW will switch back and forth from 2.2 to 0, and car starts surging.
If trying to maintain any speed below abt 40MPH, I have to ride the brakes.

If I shift into netural from any speed (even 1-2 MPH) the rpms stay at 1400, untill the car comes to a complete stop. Then it drops back to abt 950.

I've looked at my $32 bin in GMECMEdit and Winbin but I can't figure out what **** to turn.

Any suggestions?

 

What .bin file are you working from? And what all have you changed on it besides injector constant and MAF diag?

 

I'm using the ABWT.bin cause it's what the original L98 had in it when I bought the car.

I've changed the inj single and double fire sizes to 24.

I've unchecked the MAF high err flag, so I won't throw a code and restrict me to open loop. MAF seems to be working fine looking at the g/sec display on my scanner.

Changed the inj PW correction for batt voltage @ 12.8volts from 915 to 1007usecs. Trying to enrichen the idle mixture here. Hard to tell if it worked since car won't stay in closed loop very long at idle.

 

By the way, what is "maf high diag error threshold"? Just so a newbie can understand what he's reading... How are the variables related to MAF flow??? Related to voltage, or by CFM?

 

A code 33 is set when the MAF is showing over 45 g/sec AND TPS is below 17% AND RPMs are below 2000.
Don't quote me on these numbers, but you get the idea.
I'm well within all these parameters, but I still get a code 33 a few seconds after start-up (and ECM reset).
I had raised the MAF g/sec err threshold to help prevent the code. That helped a little, then it came back. I have since disabled the code 33 by unchecking the flag. Now I can get into closed loop, at least at highway speed.

 

^^^(EDIT) He beat me to this while I was double-checking my numbers, but I'll leave it anyway!

I think I can expain the "maf high diag error threshold".

There are certain criteria that, if met, will set MAF error codes 33 (high) or 34 (low). For instance, on all the .bins I've messed with, code 33 (MAF high) will set if the ECM sees greater than 45 gm/sec flow for more than one second:

1)When engine is first started

-OR-

2) While the TPS is reporting throttle is less than 25% and RPM is less than 2000.

That 45gm/sec value is the "maf high diag error threshold"

Basically the ECM thinks that the MAF sensor is reporting more flow than it should for the current operating conditions. There are lots of things that can throw this off, however. The ECM calculates airflow based upon the signal from the MAF sensor and the MAF tables in the .bin file. So, if the MAF tables are messed with, the flow seen by the ECM can be changed even though actual flow may NOT have changed.

I better stop there before I get over my head.

Jason

 

Needanother1: The thought is by increasing the threshold, the fault will be supressed. This motor has been stroked from 350 to 383.

ZZ28ZZ: What does a 350 TPI motor normally run for MAF? The CID increase is 9.4%. I wouldn't think the Err#33 threshold should be increased much past 50gm/s if the theory holds true. I may have got lost in the threads though.

I know you said you fixed the MAF but then read that you still got a code 33 and had to disable it. That jerk you felt was probably that new motor man-handling your car.

-dnult

 

I'm thinking a 350 would probably consume abt 10-15 g/sec at idle, but that's just a guess. I'm still running the 55 g/sec threshold value cause I simply haven't gotten around to changing it back to 45. After the MAF elec conn pin tweaking and cleaning, the code 33 has disappeared.

I was able to get the min idle down to abt 600-700 after fixing the maf, but the car still wants to idle at 1400 when shifted to neutral and still moving. From a standstill, when car is shifted from neutral to drive, it wants to take off. Shift back to neutral and RPM surge up to 1400, then slowly come back down to abt 900.

Immediately after adjusting the min idle, it acted like a normal car and I thought the issue was resolved; but at the next stop sign the issue returned and hasn't left yet.

 

Is the Park/Neutral switch circuit Ok? Is brake switch wired up - probably is if the TCC is working normally. Any chance your bin has the power steering circuit enabled and the line is floating? Just a few non-engine related thoughts.

-dnult

 

My scanner has a indicator on the front that illuminates when park or neutral is selected. The indicator is working fine.

Now that you mention it, I did notice the TCC indicator stayed illuminated when I hit the brakes the other day. I thought at the time it was just a delay in my scanner reacting and didn't look at it again. I've been doing all my testing on the highways around my house so the TCC pretty much stays engaged all the time. I'll be sure to check that tonight..

Is there something in the code that would increase the IAC counts if TPS was indicating idle and the vehicle speed sensor sensed motion?

I'm looking at the schematic now, but I don't see any connections on the ECM that would tell it if the brakes were being applied.

Don't remember seeing anything in my bin abt power steering.
I did notice on the 82 elec schematic there was a switch that sensed P/S press and controlled the A/C compressor clutch (it only applied to the 4-cyl eng).

BTW, for anyone following along, I fixed the MAF code 33 issue by tweaking and cleaning the pins at the MAF sensor.

 

Did you ever find the cause of your problem? My GTA does the same thing.
I have not done any engine mods and I have checked all the things you checked.

 

This isn't an IAC throttle follower issue (based on VSS)?