Got the new eng fired up last night. See sig for mods.

When eng is goosed, it revs up ok, but then dies unless I catch it.

When I tried to set the min idle (IAC driven closed and then disconnected), eng started surging badly when RPM was lowered to abt 900 RPM. After abt 4 surges, it dies.

Had a couple of vac leaks, but I'm pretty sure I have them all fixed.. (Sprayed B12 all over the intake. Tried propane too. No more leaks found)

Could still check for an internal vac leak I suppose.

EGR valve was tested and wasn't leaking before installation.

I adjusted fuel press slowly from 40 to 50 psi while eng was surging. It had no effect.

Getting a code 33. MAF high; if I remember right. Not sure what causes that error.

Using my ancient OTC MOnitor 2000 I get the following:

BLMs are 140.
INTs are 128.
Haven't got into closed loop yet.
(Can't drive it till brakes are working)

O2 voltage stays between .45 and .54 volts, and does not seem very active, although cross counts are anywhere from 5 to 25.

Didn't get a MAF reading from my scanner with eng running, but with key on, eng off, it is 015. Not sure if that's normal or not.

TPS is set to .54 volts at idle.

Batt voltage is 14.5 volts.

Water temp is 185*.

Manifold vacuum, at a steady 1000 RPM idle, is 18" and steady.

The cam (211*-219* at .050 lift, 112*LS) should idle close to a stock cam I would think.

My "custom EPROM" is a basically a stock L98 bin.
(I just cut back on the max ign advance, changed the single and double inj size to 24, and un-checked the VATS option.)

Any ideas??

I know I'll need to tweak the prom, but seems like the idle should be better than what I'm seeing now.

 

I've been helping John with his MAF problems. That seems to be a key issue here. I have a set of schematics for the vehicle and for the ECM. The MAF sensor supplies it's signal on the Dark Green wire connected to pin B12 of the ECM. The signal return is fed on a Black/White wire connected to pin A11.

From the ECM schematic, I can see that the signal line is pulled high by a 1Kohm resistor. We installed a 1K ohm resistor accross the B and C pins of the MAF and verified that we got 2.5volts drop - half of 5v. That indicates that the wiring to the ECM is good and that a 1K ohm resistor is in fact pulling the pin high. In addition, John was able to affect the reading on his scan tool which indicates that the A/D circuit is working like it should.

This leads us to believe that the MAF should be pulling the signal line low - probably with a FET or bipolar transistor. However, when the MAF is in circuit it shows 5volts accross pins B & C and does not vary with engine speed. The obvious conclusion is that the MAF is bad. However, the third MAF is installed now and the same problem persists.

Is there any chance that this is the wrong MAF for the car? What else should be considered? Currently chasing grounds to make sure that 5volts is really 5volts and not some phantom reading from a bad ground.

-dnult

 

In ref to the last post. My name is John and dnult is a buddy that helping me with this nightmare..

 

I'm having the same problem with my car. It's got a ZZ4 cam (which is smaller than yours) and it surges quite a bit and will eventually die. I've also got a code 33. I figured it was all just because it hadn't been tuned and has 24# inectors. If you figure out the problem, please let me know!

 

I adjusted the "MAF high diag error threshold" from 45 to 55.
Seems to be working so far. Doesn't give the code 33 anymore. I yet to drive the car though. That comes tomorrow..

Gave up trying to figure why the 5 volts on the MAF sensor output doesn't pull down. My scanner shows the MAF flow to be changing with throttle movement. Guess it's working after all.

 

the fact that you're not going into closed loop and that your o2 crosscounts aren't going anywhere is what I'm fixated on. Your crosscount number should just keep going up and up, and when it gets to 255, start over. The number should be constantly going and at a pretty rapid rate. if your crosscounts aren't changing, you may be too rich or too lean for it to cross over, or the oxygen sensor is lazy. a BLM of 140 says that you're looking pretty lean right now. None of that crap should prevent you from going into closed loop though. I think you may have more than one issue going on here, but right now I'm wondering if a lazy oxygen sensor isn't part of the problem.

 

From my understanding, you ARE in closed loop. If you were in open loop, you would not be able to get the scanner to pick up any readings (like BLM's, INT, etc..). I'm using diacom plus and with the o2 sensor unplugged (this puts ecm back into open loop), I dont get any readings. Is your VSS sensor hooked up and working? Try resetting your IAC and raising your base timing from 6* to 8*. Then adjust limits of your IAC to take control of idle speed quicker and shorten the rpm range of IAC control. This should help out the surging problem. Let me know if this helps.

 

My scanner (an ancient OTC Monitor 2000) lets me see the BLMs and INTs in open loop but I think they are meaningless untill I achieve closed loop.
Went for my first test drive today and car did go into closed loop.
BLMs are 140 to 150. Thinking abt adjusting the inj constant from 24 to 23.

I was hoping the idle would staighten itself out as the ECM ran in closed loop for a while. The code 33 was preventing closed loop before. Also I had open exhaust from the back of the cat. Have full exhaust now.

VSS is working good.

Not real sure abt the timing since I'm using a L98 timing cover and a 400 crank and damper.

How do I adjust the limits of my IAC?
I've tried to set the min idle but eng doesn't want to run below abt 700 rpm.

O2 sensor activity increased a lot when car went into closed loop. Sensor may be OK.