Hello there. I am working on this 2000 blazer (sister's), and its having issues.

It runs semi-well at idle, but has no power when the throttle is depressed. I did all the normal check first, It needed new plugs, wires (was original 150k mi) and fuel filter, Cat converter was replaced with a straight pipe long ago and flows good amount of exhaust. Washed throttle body and IAC valve, and checked idle vac 14 inches. so.

engine runs a little rough, but not horrible at idle, like it has for years. but try to step on it causes it to bog down, like a blocked cat or weak fuel system.

I checked fuel pressure, 60 psi and delivery, its a-ok. so I am thinking mebbe a bad sensor or such might be causing the pcm to not advance the engine timing.

Now, I connect my scan tool to the vehicle, and I get nothing. Reading up on Swartlkk's articles, I think I need to swap my BCM out in order to read the pcm, because I have the correct volts on pin 16 of the odb2 connector, pins 4+5 have good grounds, but pin 2 I get 0 volts in a steady flashing pattern. it trys to read something, but falls to zero.

I did the steps of disconnecting the sp201 splice, and connecting only the bcm up and with only the bcm and pcm, but no change. the wiring is intact and not shorted, I even test power and grounds to the bcm. but my scanner wont read it.

The next step is replace BCM. But I have a question. My old scanner, Acctron super 9145, is a few years old, is obd2, and when I connect it tries to "connect" to PCM/VPCM, and it is waiting forever. I know the scanner works on other odb2 vehicles, But I wonder that since I been reading a ton of info about scanners that wont read abs and other such modules, if I am barking up the wrong tree before I order a replacement bcm, Sigh, so I can finally scan the vehicle and see whats wrong?

Thanks for any help.

Dodgeman

 

Okay. Anyone tried swapping a BCM from a different vehicle to see if the scan tool will work? one that isn't flashed to this vehicle?

Dodgeman

 

OK. Update. Vehicle starts, run ok at idle. Increase in throttle causes engine to bog down.

Backprobed TPS sensor. Its ok and in range.
Had a spare ignition module, swapped and no change.
double check fuel pressure. 60 at idle and 70 at mid-throttle. + good flow.

I am leaning towards the PCM not advancing the ignition timing. Going to grab a timing light.

 

OK. bit the bullet and ordered a BCM. Used from a 99 blazer same config or near enough. I am betting the flash in it will work for most if not all the stuff in the truck, and leastwise, it *should* allow me to scan the PCM to see whats wrong, why its losing power above idle.

Ill post my results when it shows up.

I just can't see paying a dealer money to swap a bcm just to troubleshoot the rest of the car.

 

Put different BCM in and still scanner wont access this blazer. Going back to drawing board..

 

Thought that module's had to be programmed after installation?

 

HA! Update. Put used BCM into vehicle. NOTE: I did try to get real close as to year and features of donor vehicle to mine) and got no response. Bummed I forgot I had to go thru the checklist again. Pulled sp201 and jumpered and wham I got communication with the car. Now, I tested further And now my PCM isn't in a talking mood.

Originally I had issue with the car not running above idle, and was trying to pull DTC's. since it wouldn't, I had to replace the bcm. Vehicle has a history of crazy stuff from the BCM, light not working etc...

So I couldn't lose. Now it communicates, but it cant read the pcm. Pin b is not shorted, nor has pos volts. But I can mention it has a blinking zero volts on my DMM.

Since my drivability problem lies with a working and communicating PCM, I am going to get another donor.

Apparently, everything from base timing to simple diagnostics are in the realm of this scan tool. And I don't own a tech 2. which is smart enough to bypass all my steps, but on a budget, I am gonna try to have a functioning PCM in the vehicle before it may hit the dealer for reprogramming.

Keep you all posted.

 

Your Actron 9145 is a good entry level scan tool, but it only reads powertrain DTC's. It will not access the BCM, ABS or TCCM modules. The modules communicate with each other using serial data. A faulty BCM will not affect your ability to retrieve DTC's from the PCM.

Save your money on a timing light. It's an obsolete tool on this vehicle and won't tell you a thing. There are no index marks on the dampener or timing cover. Ignition timing is applied to the ignition module by the PCM and indicated on the scan tool. Provided camshaft retard is set correctly, ignition timing will be correct at the spark plugs. To view camshaft retard, a scan tool capable of accessing camshaft retard is required, your Actron 9145 will not access it.

Fuel pressure.... if you're seeing 70psi, there's a problem with the fuel pressure regulator or a restricted fuel return line. All fuel pressure readings are taken with the engine off. GM does not publish any engine running specs for this engine. Key ON, engine OFF, fuel pump running: pressure must be 60psi to 66psi and must remain above 55psi for at least 10 minutes after the pump shuts off. If it fails either part of this test, it does not tell you what's wrong, only that a problem exists and further diagnosis is necessary to determine the problem. Post your results using this method.

 

Thanks Captain. I'll do a more comprehensive fuel test. Yeah, I was looking for and didn't see timing marks. Ha.

Post my results tomorrow. Figures the 9145 wouldn't scan the BCM. At least its communicating with the scan tool by acknowledging the protocols, and that is what I didn't have before.

Sigh guess Ill look into newer scan tools.

 

Just a suggestion but is the distributor cap & rotor arm in good condition?
Mine started running real rough a couple years ago, especially bogging down at lower speeds. All sorts of thoughts were running through my head about what the problem could have been. All it turned out to be was a worn cap & rotor arm, I also changed out the plugs & wires while I had everything apart. Could not believe the difference in how it ran - and the gas mileage improved too!
You may well have done this but it was just a thought I had when I read your post.