1997 Chevy k1500

[Obs89]

My truck runs horrible at idle and has slight hesitation when u try to gas it. It stumbles. But once I either unplug the Maf, or ground the yellow signal wire it runs fine. My maf read 5-7 grams at idle. I have a new egr valve I also have a new temp sensor. I tried a new maf didn’t change anything. My spider injection is good. Also my tps read 0% at idle and will move when I accelerate so I believe that’s right. It came up with a code p0102 code but it seems that all the wires have ground, 12v and 5v

 

[Obs89]

Also my mad read 2.5 grams w key on but truck not running

 

[Schurkey]

What readings do you get from the MAF when the truck is driving down the road?


Fairly certain that when you unplug the MAF, the computer reverts to speed-density programming; it'll run pretty good that way. So I'm thinking there's still a problem with the "new" MAF, or perhaps with the wire harness between MAF and computer.

 

[Obs89]

I am not sure what the reading is while driving. But I did a smoke test and found out I have a vacuum leaks pretty decent. Where the spider injector plug is in upper intake the seal went out. So I am gonna replace that. And see. Some times my MAF would read high at idle until I touched the signal wire with a test light from ground. On MAF plug. Then it would read and run fine and then through the p0102 code and when I clear it it read wrong and runs bad so I believe it’s the vacuum leak throwing me in loops. But I am going to replace seal and reset computer and see what happens. I also checked the wiring it is good.

 

[Obs89]

It could be a bad MAF. After I replace the seal and reset computer and I still have problems I will switch maf and see how it does. Also my computer is reading o2 sensors and I don’t have any plugged in. Idk if that’s the safety setting or what. But what is my tps and iac suppose to read at idle I believe that’s off aswell. I’m not gonna be able to get it perfect due the moter being built but I would like it to be close as possple

 

[Schurkey]

my computer is reading o2 sensors and I don’t have any plugged in.

Holy crap, THAT has to be corrected.

 

[Road Trip]

Also my computer is reading o2 sensors and I don’t have any plugged in.

Hello Obs89,

Don't know how familiar you are with the stock '97 EFI setup, but in
simple terms it is set up to run in 2 modes:

* The 1st is "Open Loop", where the computer comes up with the
proper ignition advance & fueling based off of what's in the software
tables, indexed after the computer reads how far you've pushed on the
gas pedal, the vacuum(absolute pressure) inside the intake, etc.

So yes, in a healthy engine bay, the computer can & does run the engine
without any input from the O2 sensors. And depending upon how cold it
is and how long it takes the engine to get up to normal operating temps, this
happens for the first ~90 seconds > 5 minutes.

****

BUT, once the computer senses that the engine is up to temp AND the
O2 sensors are toggling high & low, we go into closed-loop operation
and the real benefits of an EFI-managed SBC come into play. (Benefits
defined as max efficiency & driveabillity with minimum possible emissions.)

This is why you are getting feedback to fix the missing O2 sensors asap.
IF you are living where you are no longer subject to emissions-testing,
then you still need to at least replace the front (2) O2 sensors so that the rest
of the system can then be successfully troubleshot/sorted out.

And if you need to pass emissions then you will need all (4) O2 sensors
operational. (The rear sensors are there to monitor catalytic converter
health.)

To recap, yes these engines will run with missing O2 sensors. They
just won't run as well as they should. Consider adding in those O2
sensors, and then use this setup to learn what it takes to dial in
the computer system to your powerplant. (I'm inferring that you
are planning on an improved engine?)

What you will learn in the process will pay big dividends down the road.
There's no feeling quite like driving a sharp running truck that *you*
sorted out. It's the feeling of being in control of your GMT400 destiny. :0)

By the way, welcome to the forum. I look forward to what you discover.

 

[Obs89]

Hello Obs89,

Don't know how familiar you are with the stock '97 EFI setup, but in
simple terms it is set up to run in 2 modes:

* The 1st is "Open Loop", where the computer comes up with the
proper ignition advance & fueling based off of what's in the software
tables, indexed after the computer reads how far you've pushed on the
gas pedal, the vacuum(absolute pressure) inside the intake, etc.

So yes, in a healthy engine bay, the computer can & does run the engine
without any input from the O2 sensors. And depending upon how cold it
is and how long it takes the engine to get up to normal operating temps, this
happens for the first ~90 seconds > 5 minutes.

****

BUT, once the computer senses that the engine is up to temp AND the
O2 sensors are toggling high & low, we go into closed-loop operation
and the real benefits of an EFI-managed SBC come into play. (Benefits
defined as max efficiency & driveabillity with minimum possible emissions.)

This is why you are getting feedback to fix the missing O2 sensors asap.
IF you are living where you are no longer subject to emissions-testing,
then you still need to at least replace the front (2) O2 sensors so that the rest
of the system can then be successfully troubleshot/sorted out.

And if you need to pass emissions then you will need all (4) O2 sensors
operational. (The rear sensors are there to monitor catalytic converter
health.)

To recap, yes these engines will run with missing O2 sensors. They
just won't run as well as they should. Consider adding in those O2
sensors, and then use this setup to learn what it takes to dial in
the computer system to your powerplant. (I'm inferring that you
are planning on an improved engine?)

What you will learn in the process will pay big dividends down the road.
There's no feeling quite like driving a sharp running truck that *you*
sorted out. It's the feeling of being in control of your GMT400 destiny. :0)

By the way, welcome to the forum. I look forward to what you discover.

Thank you very much and I have read that. and thank you for taking ur time out of the day to respond. It reads o2 sensors when there’s none in the truck so what ur saying is the computer is trying to say they are there?. I’m not sure if the guy before me had programmed the truck to run with out the o2 sensors.i have a 411 computer to do the swap with, just haven’t had the time and want it run right before I do so. This problem came out of no where and is seeming to be a vacuum leak after I smoke tested it. And currently waiting for gaskets to arrive so once they do I will update every one and see if that fixes it. But it just confused me on how is the computer reading o2 sensors when there isn’t any. Even when I have MAF plugged in I get no check engine light , but two codes pop up saying 02 sensors failed or not reading. So basically what I’m gathering from you is that the computer is in a safety mode and the computer is telling itself that there is 02s. Sorry if I confused anyone I am still learning and only at the age of 18 and not familiar with the 97 computer and electoric system. I’m used to my 89 cut all the computers out and put a carbed z-28 355 out of a 69 camero that had been buit from friend who does racing.

 

[Obs89]

Holy crap, THAT has to be corrected.

Any suggestions on how. I have a spare black box I can try. Just to see how it does but I also have a 411 computer like stated above.

 

[Schurkey]

How many O2 sensors is your truck supposed to have? My '97 has four--two before the catalysts, and two after. Other applications might only need 2 or 3 O2 sensors.

Old O2 sensors are not to be trusted.

Buy the right sensors for your truck, install them where they're supposed to be, and make sure the wiring to the computer is good. Don't buy cheap-junk sensors. Get decent ones--ACDelco or NTK are my first choices.