SoGT related (kinda of) DM files

[Tophatjimmy]

My dad has been having a lot of trouble with his Blazer for awhile, so we made a Datamaster run. I'm posting it up here because his Blazer has the same N/A CPI engine as the SoGT and I figured you guys might be able to help decipher why his truck is acting so weird.

Anyone feel generous enough to take a look for me?

Thanks in advance

 

[jjorgensen52]

Re: SoGT related (kinda of) DM files

Did you use the CPI version of DM? ... just curious. I'll take a look tomorrow, but I'm no expert at reading DM for the CPI's . I have done a lot of manual troubleshooting though :lol: ... what kind of symptoms is the truck experiencing?

 

[Tophatjimmy]

Re: SoGT related (kinda of) DM files

Yes, I used DM version 32xE6 for 1993 L35 engine code W w/4L60E trans.

This is kind of a long story, I'll try and sum it up as best I can:
My dads truck was running really bad and really rich and he kept fouling plugs. He took it to the dealer and they put a new injector in it because one of the injector tubes was cracked and leaking. Since then, his fuel mileage went down 3 mpg. He used to get 19-20 mixed driving, now he regularly gets 16-17 mpg, which he is not happy about.
Last fall it started starting really hard. Takes 3 or 4 tries to get it to start. He told me that if he pumped the gas pedal while it was cranking, it started a little better. Made no sense to me, but it's true. Once it does start, it bucks and misses for a few seconds, then smooths out and throws a code 42.

Hell drive for a few blocks and the light will go out. It does this pretty regularly now. It also will not shift down into passing gear ever.

So we ran Datamaster last night. Since I just started using it, I'm not yet famiiar with all the data and what it SHOULD look like but I did notice a couple of things. During the run, we got 2 codes thrown, but the light never came on. We got code 32 and code 43. We also made a WOT run on the freeway, but his TPS% was only 72.5 and his TPS voltage was 3.32volts. Maybe this is why his tranny won't downshift??? At idle, the TPS% is 0 and the voltage is 0.61.
We checked his throttle cable and with his foot to the floor, the throttle valve is on it's stops, fully 100% open, so it's not a loose TV cable.

I'm thinking bad TPS sensor maybe???

Not sure if this is normal or not, but just after we started it up, sitting in the driveway at idle, the spark advance was ALL over the place, jumping around sometimes 6 - 8 degrees.

Also, his speedometer is off. At what his speedo says is 35, DM said 38. At what his speedo said was 70, DM said 65. Weird....

He thinks maybe the computer is going bad? I dunno.
Bad TPS sensor??

I can send the .uni file anytime.

Thanks

 

[jjorgensen52]

Re: SoGT related (kinda of) DM files

Well, I see a whole host of symptoms here.

First, Codes
32 - EGR failure. This one is going to give either no EGR, or EGR stuck open. That would explain dropping fuel mileage and hard starting (exhaust in the cylinders = no good). You should pull it off and check for carbon build up and see if it's sticking ( should be able to operate the valve by hand, if you can't it's going bad).

42 - EST circuit. Given that and what you said about your timing at idle, I would get the ignition module checked (under the dist. cap, usually autozone or similar can check them). The truck will bypass the ign mod. after it tries to run with it if it has gone bad, and it will smooth it out but you loose your computer timing control and thus the timing reading will be off.

43 - Knock sensor wiring open or shorted. L35's have two knock sensors, one on the back of the passengers head and one on the side of the driver's head. Check those out and see if they're firmly seated, not loose, etc. Also, if the wires are pinched that could be problematic. I know I've knocked my driver's side off changing the CPI injector.

For the 4l60-E, the TPS being off will cause the truck to not downshift. The voltage, IIRC, should be around 4.6v at WOT, so I might try replacing that too. Although I believe there is a spec in the factory manual for the resistance in that sensor, I'll see if I can't find it tomorrow.

As for the speedo being off, luck of the draw. I know mine is wrong, they just wear out over time.

One other hard start thing is fuel pressure. I assume the mechanic would have checked that, but if the truck isn't holding over 50 psi it won't start spraying fuel the way it is supposed to. I had that problem with my GT

 

[Tophatjimmy]

Re: SoGT related (kinda of) DM files

Thanks a ton!

I want to say my dad has replace the ign module, but I'm not sure. I know he took it out and had it tested. He tested it himself and it was bad, so he took it to Napa and it tested good. He may have just put it back in.

The EGR is probably bad. It had thrown codes before, so my dad just has taken it off and cleaned it out. Probably no good now. DM was showing EGR activity during driving though...

I'll have him check the knock sensors. He's been scratching his head over code 42. His manual says "EST showing retard for too long" in the code section. Electronic Spark Timing right? He couldn't find any other reference to EST in the entire manual. Didn't know what it was...

We'll have to get a FP gauge to check the FP. I haven't looked too closely at his engine, but is there a schrader vavle in there we can connect a gauge to?

 

[jjorgensen52]

Re: SoGT related (kinda of) DM files

Yep, EST is electronic spark timing. It is also possible your dist. has migrated out of alingment and you need to reset it. To do that, there is a little tan wire under the carpet right at the front of the passenger's footwell. Disconnect it, fire it up and it will reset the electronic timing, and you can also check the mechanical setting. Ought to be around 8* mechanical advance.

As for the EGR, you can have activity and still have it sticking, as the activity is the computer trying to control it and not the valve responding.

IGN mods are usually not too expensive, so it wouldn't hurt to replace it if even one test said bad.

There is a fuel pressure valve, it is sticking straight up at the back of the manifold (this pic is taken from behind the motor :lol: )

 

[Tophatjimmy]

Re: SoGT related (kinda of) DM files

OK. My dad had replaced the ign module. Took it and the stock one to AutoZone and they both tested good, but still getting code 42?? Anything else that might cause that code?

Unplugged the tan wire and checked the timing 0* on the nose as per the Haynes manual. Plugged the tan wire back in.

EGR valve is less than 2 years old. Used to throw codes all the time so dad had it replaced. Can't take it out and clean it up much because it's electrical solenoids, not a vacuum diaphram.

Knock sensor is an unknown right now. The one behind the motor is gonna take some dedicated time to get to and the connector for the one on the driver's side head was so brittle from the heat, we dared not to take it off.

All in all, still hard starts, still runs like crap, still throws codes. :tdown: :rant:

 

[jjorgensen52]

Re: SoGT related (kinda of) DM files

The EGR valve that actually sticks is the mechanical passage, carbon can build up and restrict it from opening and closing properly (especially if the truck was running rich).

As for the EST, the other part of the circuit that could throw that would be the reluctor in the dist itself, not sure if you can replace that but if the input to the IGN mod was messed up then it would be as well.

As for the hard starts, I would definitely check the fuel pressure for that.

Also, did you try the TPS? I will look that up tomorrow, I can't remember the resistance range for that