How do I OM out the sensors for a 1997 5.7 vortec.

[oniontheoreo]

So my 97 5.7 vortec has had a backfire problem for about 2 - 3 months now and it's driving me insane. It has a cylinder 2 misfire right now but when it doesn't misfire, it runs as smooth as glass. I've replaced my fuel pump, coil and the icm next to the coil, the full distributor along with plugs and wires, both intake gaskets (however I might has messed up on the lower) replace the injectors with the better ones. Also I used acdelco where I could, some of the engine sensors or duralast. I also have video of what my o2 sensor are doing and 2videos of the misfires, one is the first start up after I put the new fuel pump in and the second one is after the engine had ran for a bit. Side note as well I do believe I have lifter tick as well but idk if that would effect that. Please help I don't wanna drive my backup **** box anymore

 

[TonyM]

What sensors do you want to ohm out? The O2?

 

[Erik the Awful]

Ohming sensors is a suboptimal strategy and can lead you to replacing stuff unnecessarily. The fact that you're trying to ohm sensors to troubleshoot a single cylinder misfire tells me that you're already chasing your tail. Your sensors affect multiple cylinders.

Pull your plug and read it. If it's lean, you likely have a bad poppet on the fuel spider. If it's wet with fuel you have an ignition problem - not likely since you've already replaced everything and the problem didn't change. If it's wet with oil you have a mechanical problem, like bad valve seals.

Most importantly, get your hands on a scan tool that can read data stream. That will show you if a sensor is bad without fiddling about trying to get ohm readings.

Do the diagnosis. If you don't know a next step, ask and we'll give advice.

 

[Schurkey]

^^^ What he said.

In the time it takes to "ohm out" two sensors, you could have connected a scan tool and verified ALL of them, and without rising wire harness damage by poking sharp probes past the sealing grommets. The mental image I want you to have is "Alien abductions" and "Rect_al Probing".

Then, with the scan tool connected, you could verify the computer outputs to the IAC, the EGR, the electronic spark advance, look at the fuel trims, verify misfire counts, and so much more.

"Ohming out" sensors does not verify the wire harness between the sensor and the computer. The sensor can be perfectly good, but maybe the computer doesn't get the sensor signal due to a faulty harness.

Trying to fix a computer-controlled vehicle without being able to communicate with the computer is two steps away from hopeless.

You NEED a scan tool to do this efficiently.

What is your fuel pressure at prime and under load? How old is the fuel filter?

Vortecs are notorious for failed distributor caps. Cheap caps seem especially prone to failure.

Are the spark plug wires routed EXACTLY as shown in the service manual? No broken looms, no tyraps holding a bundle of wires together?

HOW, exactly, might you have "messed up" on the lower intake gaskets?

 

[oniontheoreo]

I have a scan tool and it's how I know I have a misfire on cylinder 2 + the count, I just really need to know how to ohm out the map, maf, and o2 sensors. I also have data for those sensors. The distributor is brand new and the rotor is a duralast one because it's a bit more insulated the the accel and others. On the lower intake gasket where you use like a gasket maker, it was my first time doing it so idk how I did. The whole spider, fuel pump and filter are new. Also me being stupid forgot to say it has a code for ignition control circuit voltage high. That's the other sensor I would like to ohm out, not the actual icm but the "secondary" icm unit next to the coil. Have a video of what the o2 sensor are doing. And how would I know if one of those sensors are bad when scaned by a tool

Ohming sensors is a suboptimal strategy and can lead you to replacing stuff unnecessarily. The fact that you're trying to ohm sensors to troubleshoot a single cylinder misfire tells me that you're already chasing your tail. Your sensors affect multiple cylinders.

Pull your plug and read it. If it's lean, you likely have a bad poppet on the fuel spider. If it's wet with fuel you have an ignition problem - not likely since you've already replaced everything and the problem didn't change. If it's wet with oil you have a mechanical problem, like bad valve seals.

Most importantly, get your hands on a scan tool that can read data stream. That will show you if a sensor is bad without fiddling about trying to get ohm readings.

Do the diagnosis. If you don't know a next step, ask and we'll give advice.

 

[Schurkey]

I just really need to know how to ohm out the map, maf, and o2 sensors. I also have data for those sensors.

What would you learn from "ohming out" the sensors that you wouldn't learn--easier and better--from the scan tool?

I don't know of a procedure for ohm-testing a MAF. Never done it. Far as I know, they work on an AC frequency, not resistance. Similarly, I've never put an ohmmeter across a MAP or O2 sensor. I'd have to check the service manual to see if there's an applicable resistance check. A voltage check with a multimeter is possible, but again, you're getting the same data via the scan tool, faster and easier.

The distributor is brand new and the rotor is a duralast one because it's a bit more insulated the the accel and others.

My concern is that a "new" distributor is almost certainly a Communist-Chinese unit, with a cheap distributor cap.

On the lower intake gasket where you use like a gasket maker, it was my first time doing it so idk how I did.

Are you talking about the "China Wall" at the front and rear of the block, or are you using RTV to stick the gasket to the cylinder head?

If this is the "China Wall", all you need is enough RTV to be squeezed between the manifold and the block--so that there's no voids from one side to the other.

The whole spider, fuel pump and filter are new.

Excellent. What is the fuel pressure?

Also me being stupid forgot to say it has a code for ignition control circuit voltage high. That's the other sensor I would like to ohm out, not the actual icm but the "secondary" icm unit next to the coil.

There is no "secondary" ignition module. The unit by the coil is the only ignition module. You wouldn't test an ignition module with an ohmmeter anyway.

Download the service manual set procedure for your vehicle from the links in the "sticky" section of the Engine forum. Follow the service manual diagnostic procedure for that "ignition control circuit high" trouble code.

Have a video of what the o2 sensor are doing. And how would I know if one of those sensors are bad when scaned by a tool

Generally, they have low cross-counts; and maybe they don't switch across the full voltage range. You might also see trouble codes for the O2 heater circuit, too.

When it comes to O2 sensors, I learned the hard way that sometimes replacing them is easier than properly diagnosing them; especially if they have more than 50K miles on 'em.

It's one of those deals where it's possible to prove they're bad, but truly difficult to prove they're good.

 

[oniontheoreo]

56-7 psi Key on
52 psi running
58 psi after idle
I know that's a little on the low side but is a brand new pump, so my gaude might be off. The distributor is an accel one not chinesium, the only reason is got a duralst rotor is cuz I broke it and need a quick replacement. And those china walls just seem sketchy to do but I didn't know if I placed enough along the wall compared to the spots where it meets the heads. I also have a Haynes manual, do they have the procedure in it? I'd assume but idk for sure. And I ask for the maf and 02 sensors is because it feels like it's a closed loop for those 2 (again idk) and as far as I know that's a way to test them. I also have a video of the misfire counts

 

[Schurkey]

Accel 59132? I bet it is Chinese, and Amazon has multiple reviews saying the cap or the rotor failed almost immediately.
www.amazon.com/ACCEL-PERFORMANCE-DISTRIBUTOR/dp/B07GFVMNN8/ref=sr_1_9?crid=NSTLIMVR5Q0

If you don't have an oil leak, the sealant on the China Walls is fine.

Your Haynes manual will make great emergency toilet paper. Download the REAL service manual set for your '97 from the links in the Sticky section. You can look up proper test procedures for each sensor in the REAL "Genuine GM" service manual.

 

[Erik the Awful]

And those china walls just seem sketchy to do but I didn't know if I placed enough along the wall compared to the spots where it meets the heads. I also have a Haynes manual, do they have the procedure in it? I'd assume but idk for sure.

It won't cause your misfire.

And I ask for the maf and 02 sensors is because it feels like it's a closed loop for those 2 (again idk) and as far as I know that's a way to test them.

You cannot check the condition of the MAF nor O2 sensors by ohming them. The MAF sensor operates by passing current through a conductor that's exposed to the air stream. If it takes more voltage to keep the current up, the computer knows there is more air flowing. In a static environment the resistance in the conductor is constant. O2 sensors use a chemical process to generate their own voltage that the computer reads. You have no way of checking the running condition of these sensors by ohming them. At best you can tell if there's something seriously broken in the sensor.

Buy this cap and rotor set to eliminate it as a possibility.

More Information for UNITED MOTOR PRODUCTS DCR820X

 

[AuroraGirl]

What would you learn from "ohming out" the sensors that you wouldn't learn--easier and better--from the scan tool?

I don't know of a procedure for ohm-testing a MAF. Never done it. Far as I know, they work on an AC frequency, not resistance. Similarly, I've never put an ohmmeter across a MAP or O2 sensor. I'd have to check the service manual to see if there's an applicable resistance check. A voltage check with a multimeter is possible, but again, you're getting the same data via the scan tool, faster and easier.



My concern is that a "new" distributor is almost certainly a Communist-Chinese unit, with a cheap distributor cap.


Are you talking about the "China Wall" at the front and rear of the block, or are you using RTV to stick the gasket to the cylinder head?

If this is the "China Wall", all you need is enough RTV to be squeezed between the manifold and the block--so that there's no voids from one side to the other.


Excellent. What is the fuel pressure?


There is no "secondary" ignition module. The unit by the coil is the only ignition module. You wouldn't test an ignition module with an ohmmeter anyway.

Download the service manual set procedure for your vehicle from the links in the "sticky" section of the Engine forum. Follow the service manual diagnostic procedure for that "ignition control circuit high" trouble code.


Generally, they have low cross-counts; and maybe they don't switch across the full voltage range. You might also see trouble codes for the O2 heater circuit, too.

When it comes to O2 sensors, I learned the hard way that sometimes replacing them is easier than properly diagnosing them; especially if they have more than 50K miles on 'em.

It's one of those deals where it's possible to prove they're bad, but truly difficult to prove they're good.

ive found good original O2 sensors can become slow and while they work, i improved my idle significantly on my park avenue with a new o2 from denso.

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