Running poorly/misfiring, code 33

**JeepsAndGuns** · 07-18-2023

I can pick up a vac gauge and hook it up this weekend.

However, any idea why I can not get any map sensor reading on the datastream?
I have bench tested many ecu's in the past and used a hand operated vac pump on the map sensor and saw it on the datastream.
I am just confused as to why I am not seeing it now.
It is acting like either a broke wire between the sensor and the ecu, or it is not getting power. However I have tested both and they both appear to be good.

**NomakeWan** · 07-18-2023

Well first I'd do a sanity check. While the car is running and you're connected to the ECM and datalogging, unplug the MAP sensor.

What happens?

**JeepsAndGuns** · 07-19-2023

It will not stay running on its own right now. I have to keep it running by feathering the throttle. If I let off, it stalls within a second or two. Not enough time to get to the sensor and unplug it.

**steveo** · 07-19-2023

probably the map sensor is faulting and being overridden with a default value try resetting the ecm

**JeepsAndGuns** · 07-21-2023

That was one of the early things I did with no change.
I also tried another spare ecm I had with no change.

When I pick up a vac gauge this weekend, I'm gonna try and get some back probes and test the map sensor pins with the sensor plugged in.

**steveo** · 07-21-2023

doesn't take much to verify the wiring is good too, just backprobe the pins to the ECM

**JeepsAndGuns** · 07-24-2023

Well the parts store did not have a vac gauge or back probes.
However I feel like the issue is electrical and not mechanical, seeing as how it was intermittent at first. I may end up ordering a vac gauge online just to have one.

I did raid my wife's sewing kit for a needle and used that as a back probe.
I ended up not having anywhere near as much time this weekend as I thought I was going to have.
With the sensor plugged up and the ignition on (engine not running), I have 5v at the power wire, and have 4.88v on the sensor out. The voltage drops as I apply vac to the sensor.
I then go to the ecu and check the pin there. I have the same voltage readings (ignition on, engine off).
So it would appear it is making it to the ecu. However I did not have the laptop hooked up.
I took loose the distributor and gave it about one degree of a turn just to see what would happen.
I got it to fire off and run. Still ran like crap and missfired like crazy, but after about 30-60 seconds, I got it to idle on its own (still running poorly).
While it was running, I was feeling around the wiring and just looking things over and it suddenly stumbled badly and died.

I am starting to think I have a bad wire, that is somehow testing good, but for some reason is not getting the signal to the ecu. Or is showing good when I test it, but is not when the engine is running (for some reason)

I have some spare pigtails and terminals for the weatherpack connector for the map sensor, but I do not have any spare pins or pigtails for the ecu connectors. I do not really want to cut the wire close to the ecu to run a new wire, only to find it is that that wire. I need to find some pins and make a temporary new wire from the map signal to the ecu and test it.