This has got me stumped. I don't know what is causing this. Here we go...

1985 LB9 305 with 70K on it. The engine runs good and idles good. I know I need to do the injectors, they bleed down. I hooked up my father's old OTC scan tool to see what's going on with the sensors, and you can smell the engine running rich. The CTS read 74* with the engine cold and as the car warmed up to operating temperature the scanner reds 22*? This has me stumped, maybe the scanner is messed up?

Also, I metered the pin C10 at operating temperature. It metered as it should at 1.6 volts.

I wonder if I have some ground issues here or something. I know as a weak connection gets hotter, it's resistance goes up.

Just wondering if anybody else has seen this happen before?

 

Also, no codes showing.

 

Need to check the actual sensor resistance values at various temps
Can do it in place by disconnecting the plug and probing the 2 terminals of the CTS

https://www.thirdgen.org/forums/post...095-post3.html

 

It's brand new. I will try tho.

Thanks

 

Do the CTS diagnostics.
http://chevythunder.com/cts_diagnostics.htm
http://chevythunder.com/cts_diagnostic_pg2.htm

Could be a wiring / connection / ground problem as you previously noted

 

The ECM has ground, as does the D13 pin at the ECM.

Gonna test voltage next.

 

We don't need minute by minute updates.
Just do ALL the CTS tests and fixes as required ,if that doesn't solve it report back.

Test the CTS resistance , being new is no surety these days that something actually works

 

Ok, so I start the car this morning and go for a ride. It ran good, with higher voltage on the gauge seeing that I gleaned all the grounds on the ENTIRE engine bay. I removed the paint behind the grounds mounted to the alt bracket, firewall, core support and inner fenders. I also took that stupid star washer out and placed the O rings directly against the steel, which gives more grounding surface area that the points on the star washers.

I hooked up the scanner again, this time I see there's a separate code for scanning TPI. How did I miss this before? The temp gauge was reading 190 ish and the scanner was reading 108. I just put in an adjustable fan switch and don't know what I should go by.

Any ideas?

 

Also, the O2 sensor won't go into closed loop.

 

108 degree C = 227F

Get a IR temp gun or some other means to check what the actual engine temp is so you know which is correct

 

Ok, thanks. I'll grab one and see what this thing is doing.

 

Just took the car on thruway for a bit, bout a 20 min ride there and back. About halfway through the ride the check engine lite came on. I scanned it and it says code 26 and code 54.....ugh!

 

So I googled code 26 and found this.......

1) Cooling fan(s) inoperative

2) Poor driveability due to 100% canister purge.

3) Coolant light "ON" all the time, "OFF" during bulb check.

4) EGR inoperative - Code 32.

5) TCC inoperative

And this for code 54......

1) Faulty fuel pump relay.

2) Faulty connection at ECM.

3) Faulty oil pressure switch.

4) Faulty ECM.

I wonder if I tripped the fan light by installing that new fan controller?

As for the fuel pump, I will check the grounds and the relay socket.

 

Another good reason to chuck the 870 across the street. the egr temp switch is really problematic with tpi and you can only get it from zif corvette. The egr solenoid should ohm around 26 IIRC. I think your could was off and maybe it was a code 25.

http://www.chevythunder.com/Flow%20chart%20index.htm

 

I'm gonna do the 165 swap. There a member here that has the ECM for sale, but I don't know if I should get e new one or the used one?

 

I think new ones are $80 at rockauto.com but that has a core charge as well. With a used one you can get a memcal any 86-89 tpi memcal can be reprogramed to work. I would just stay away from the hypertech tpi maf memcals I. Have had issues with some of them especially ones made for 87 for some reason.

 

What's the part number for the fuel pump/ oil pressure switch? Not the sending unit, thanks.

 

Ok, so I got around to checking the driver's side head grounds. THEY WERE ONLY FINGER TIGHT! I was able to spin them off by hand. I cleaned them all up and tightened them up good. I'm thinking that could've been my issue.

I also looked at the fuel pump relay. It had three wires that had 1/2" of bare wire showing at the connector. I ordered up a new pigtail from Hawk's and a new relay from Advance.


Btw.....how the heck do you get at the MAT sensor? Holy cow! It's buried under that upper
Plenum!

 

I like to use the gm weather pack seal 14089936 acdelco 15-8240 pigtail PT1115, you have to pull the plenum to get to the mat.

 

Is it a 2 prong switch ?

 

Yes it is. I think I've found it from Advance. I'll grab the part number.

 

After doing some more diagnostics on the car, I drove it the other night to a party. Again the light came on. Code showed was for low voltage to fuel pump....AGAIN! I know I'll be installing the 165 ECM thin winter. But should I be worried about the pump?

Btw, the car ran flawlessly the whole time. There was never a sputter or hiccup at all.

 

The Low voltage monitor bye the ecm is done bye voltage feedback at the fp relay. I would check that first the real voltage at B2 (red wire of the ecm) and the connection at the ops.

 

i soldered in a new pigtail on the FP relay and replaced the relay. I will have to do more diagnosis before it gets tucked away for the winter.

 

Would/could a weak alternator cause this code too? I notice as the car warms up the voltage on the gauge drops.

 

A high alternator output causes a code 53, A low voltage there is not a code for the charging system but if it is low the injector vs battery offset causes the engine to run real rich and you could have a code 54 as well.