The more I read, the less it makes sense!

Hey Fellas, I rebuilt the 350 in my 94' Chevy C2500 about a month ago. It runs great! I do have a low idle issue though. So, I decided to venture into this world and ordered an ALDL cable which should arrive tomorrow. I downloaded WinALDL to my laptop. I'm not yet familiar with anything you guys talk about so I'll just shoot the numbers and hope you know what I'm talking about. My ECU #16205995, BLHH. I believe the "mask" (I think that has something to do with the program) is $0D. Although I have a custom prom the one that came out is a 27C512. My truck has the 12 pin connector OBD1. I just want to see what's going on behind the scenes while driving, and figure out my low idle. My vacuum is where it should be with the cam I installed at 18" at idle in park. My timing is 4* advanced. My fuel pressure is set at 16psi. I have a new IAC valve, and just about every other sensor is new and I've checked them with a multi-meter for voltage from the connector and resistance at the sensor. All good! My idle is fine in park, about 800-900 RPM's (that's IF my Sunpro Tach is reding the HEI correctly), trouble is once it's warmed up, in gear, and I put a load on it with power steering, A/C, etc. it falls to about 200-300 rpm. My battery voltage is low at that point as well, so, I'm wondering if maybe I bump up my alternator amps, (the battery tests good), it will help get the signals back to the ECM or whatever. I AM running an MSD CDI box, Stereo amplifier, and heavy duty headlight harness directly off the battery and that MSD alone needs a constant 5-6 amps to function correctly. Also, should I run something other than WinALDL? Not that I'll be able to understand it! Thanks!

Hi. Welcome to the site.

Not a bad start, at least as far as first posts. The mask ID is a shorthand way to identify the program your computer is using. I believe yours is actually $0E, but don't get too worried are three different ones used in your pcm. WinALDL is free and plenty of people use it, but if your going to go beyond basic diagnostics you should consider TunerPro which does both logging and tuning. Either way, the datastream definition you're using should match the mask or you're liable to get incorrect data.

First question: Is the rebuilt engine a stock replacement with stock cam?

Second question: Why is your timing 4 degrees advanced? Is that spec? Most trucks are 0 with some early ones set at 6 deg? I don't remember any set at 4. Then again I have trouble remembering an anniversary even after 22 years. :mad1:

Third question: Is your engine stalling? If you're concerned about an RPM drop but the engine isn't stalling, and it's a stock replacement, it's probably worth it to learn what idle speed the computer wants to see when the truck's in gear.

Fourth question: Does the PCM recognize that the vehicle is being shifted into gear?

Fifth question: Is the A/C OEM or is it an aftermarket installation?

The PCM only has a couple of methods for correcting for load at idle. Increasing spark advance is the fastest method and increasing IAC is the second fastest method. This signal, if present, indicates the need to rapidly increase timing. The ECM will typically increase spark advance slightly and increase IAC slightly when the selector is shifted out of "P" or "N." It will then begin attempting to achieve a desired idle speed. Loads are accounted for through the manifold pressure sensed by the MAP sensor, and sometimes by additional sensors. For example, if a power steering pressure switch is present that signal triggers a small increase in advance to make up for additional load. If system voltage changes, there are corrections in place which attempt to account for the change. Typically stock applications do not show dramatic rpm changes with a couple of volts difference but modified systems can be subject to larger variations. Ultimately, you'll want to get scanning software working to see what the ecm is doing. Switching to Tunerpro will allow you to share recordings of your data (called logs) so others can view them. Switching before you get comfortable with another software package will probably reduce your stress level.

HTH

Thanks for the valuable info and quick reply! I will answer your questions as accurately as possible. 1. The only thing stock about the engine is the TBI heads. The block is bored .30 over and square decked with flat top pistons. The cam is an Edelbrock #3702. Brian Harris of Harris high performance made my chip for that specific cam profile. It's got a 2000 stall converter, Modified throttle body with pod spacer, custom 3" exhaust with Gibson headers, thermal 02 sensor, I could go on. 2. The timing is advanced at the recommendation of Brian Harris after talking to him about my low idle. Stock is supposed to be set at 0 with the EST system bypassed. I don't really notice a big difference one way or the other though. 3. The engine doesn't stall. When it's warmed up, in gear, and I put a load on it by turning the steering wheel, the RPM drops, my voltage drops, and the lights dim. 4. I'm not sure how to answer this question except that I don't know if the PCM recognizes that it's in gear. 5. The A/C is completely rebuilt with stock ACDelco parts. I'm going to get TunerPro today. Thanks for the suggestion and your help!

The RPM drops and then just stays low? That could indicate the IAC motor isn't moving properly when it's commanded. The PCM just signals it to move but can't tell if it really moved or not.

Tuned by TBIChips.com - just do a search here. Not much positive to be said.

The rpm drops and stays there when in gear, with the brakes applied. My battery voltage drops although the battery reads 12.8 on a multimeter. When I give it gas, there's about a half second lag, then it takes off. The IAC is a brand new ACDelco that I can hear working when the air flow drops as the engine warms up. My TPS checks out as well. Who do you recommend for a custom chip? Thanks!

The chip Brian Harris from TBI Chips screwed me on was set to idle at 525 with 16 degrees timing...didn't work. Well, actually, all six of his pathetic attempts of a "tune" failed. I'd forget the TBI Chips tune and start over fresh with someone on here. He is a con artist. There are several tuners here that could handle this. My truck ran better with the stock chip and 8 degrees of base timing added than anything Brian Harris could do.


BLG

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Originally Posted by BLG355

The chip Brian Harris from TBI Chips screwed me on was set to idle at 525 with 16 degrees timing...didn't work. Well, actually, all six of his pathetic attempts of a "tune" failed. I'd forget the TBI Chips tune and start over fresh with someone on here. He is a con artist. There are several tuners here that could handle this. My truck ran better with the stock chip and 8 degrees of base timing added than anything Brian Harris could do.


BLG

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That sucks! As soon as I figure out how to get tunerpro to work, I'll check it out. Thanks! And, WHO WANTS TO MAKE ME A CHIP, PLEASE?!