redbandit98

hey guys, i had a big long explanation but i will save you from having to read it. I realize this is a tuning section. I am a lowly shade tree mechanic with a simple question. If its out of line please delete it and accept my apology. Can the ESC board on the memcal be tested by someone who burns chips etc? I have a 1995 suburban that's giving me hell with a code 43.(I know, a truck not a third gen but you guys tune and work on them way more than the guys on those forums) I've ohmed the new and old sensor, both checked about same. Ive got 5 volts at the sensor. I'm getting the code 43 about 15 seconds after startup. Sadly, I have no software for data-logging. I have some scan tool stuff (auto-engineuity) buts its all ob2. Again, I know this isn't the help section of the trouble code forum, or even the right forum to ask it on, but you guys tune a lot on these older systems and I would really appreciate any help.
Matt

RBob

iTrader: (1)

Sounds like the wrong knock sensor. They should measure around 3,900 ohms (3.9K ohm). If 100,000 ohms (100K ohm), it is the wrong sensor.

Can also do another test: key-on, engine-off, remove the wire from the knock sensor and measure the voltage between the connector and the engine block.

As you found before it should be 5 volts. Now jumper between the connector and knock sensor and measure the voltage again. It should now be 2.5 volts (+-1 volt). That is the test that is failing and why code 43 is being tossed.

Moving to DFI & ECM...

RBob.

redbandit98

That's another source of mystery. I have read that it should be 3900 and it should be 100k. I spent about two hours trying to find a definitive answer and I came up with both answers. I kept coming up with the early model tbi and tpi all used 100k sensors, while the later model (lt1, CPI trucks etc,) used the 3900 ohm. Are you absolutely positive they are supposed to be 3900 or so? Im not questioning your knowledge by ANY means, I just keep hitting a wall when trying to get an exact answer. I appreciate the info and the extra test procedure . I will do some testing and report back.

RBob

iTrader: (1)

The '91 through '95 TBI trucks used three different types of ECMs/PCMs. It is dependent upon the year, type of EGR, and type of transmission.

The trucks with manual transmissions and a standard EGR used the old style C3 ECMs. These also used an external ESC filter, along with a 100K ohm knock sensor. To test the ESC system there is the run-away knock detection. Then usually a forced knock test (advances SA until the engine knocks and the ECM sees it).

When an E automatic or a linear EGR was used, then a PCM is used to control things. These have a MEMCAL with the ESC filter integrated into it. In this case there is a test of the sensor and wiring to it. This is where the ECM measures the voltage on the sensor wire as it enters the ECM.

If a 100K knock sensor is used, the test fails. These PCMs used the 3.9K knock filter.

All '88 - '92 f-body TBI vehicles used the 100K knock sensor.

All '85 - '89 f-body TPI vehicles used the 100K knock sensor.

All '90 - '92 f-body TPI & MPFI vehicles used the 3.9K knock sensor.

Of course the odd one of the bunch is the '89 TTA with the SFI system. It used the 100K knock sensor as it used a C3 ECM and an external filter.

RBob.

redbandit98

hey I REALLY appreciate that information. I'm guessing someone changed the knock sensor before me trying to fix the code as well. I will try to go to the parts house and ask for a 91 Fbody knock sensor and I will take my meter with me to verify it. Just for kicks the PCM is a 16196395, I also took some pics of the memcal and knock filter numbers incase I had to try and source one. Again, many thanks
Matt

redbandit98

thought I would report back and say that it did fix my problem. I would have never got the right part at the store. I usually look online first to see if there are any circumstances they will ask for so I'm not caught off guard. Looking online it said there were two sensors, one for I think a 16 bolt and one for a 17 bolt trans. I counted the bolts and went to the store. I told them 16 and thats what they gave me. Turns out I needed the other one, even though I had the 16 bolt trans. I'm guessing the 17 is a 4l80 instead of the 60E? Either way I asked for one from a 91 fbody and it was the same sensor for the 17 bolt trans. What a fiasco. Thanks again for the help. I would have pulled whats left of my hair out trying to find it.

RBob

iTrader: (1)

Good that you got the correct knock sensor. The strange part is, is that either E trans uses the same resistance knock sensor.

It only changes in resistance when a stick trans is involved. There have been times posted here where the person has taken a DVM/MultiMeter to the auto supply store to verify the sensor resistance.

Anyway, good to go....

RBob.

redbandit98

throw me in that crowd too. After the first go round, I took my meter with me.