98 Tahoe - Cylinder 6 misfire - fuel or ignition problem?

[HoeLV]

Thanks @east302 , I'll look into those and see what applies.

@exp500 I will have to borrow a fuel pressure test kit again. Speaking of 02 sensors, I was watching all 4 (bank 1&2, sensors 1&2) and the first 3 looked to be normal. Bank 2, sensor 2 was basically flat lined. Conveniently its the same one I replaced in December (I believe with a bosch branded replacement). I'm wondering if I should put a delphi or Delco in.

 

[exp500]

I believe Denso was OEM for O2. I've had good service from them as replacements.

 

[east302]

What voltage is that downstream sensor sitting at?

It should be pretty steady and not oscillate like the upstream, but if it’s fixed below 26 mV it should trip a low voltage code P0157. Try swapping it with the other downstream sensor and see what it does.

For comparison, here is my son’s 98 after a cracked head (Bank 1) flooded the exhaust and locked the engine. Bank 1 downstream sensor implies that the catalyst isn’t doing anything productive. Bank 2 is steady. Whether it’s “too” steady is unknown to me, but it is a new converter, doesn’t trip a code and responded the same way after replacing the bank 2 downstream sensor. I think it’s ok.

Either way, the cause of any catalyst inefficiency would be the first thing to remedy.






To me, your issues started with 5 and 6 misfires that appear to have been resolved after the ignition work. Following the MPFI replacement, you got a #2 misfire that doesn’t look to be ignition or fuel pump related.

It’s easy to spend someone else’s time and money but that injector assembly seems a reasonable culprit. If it can be warrantied out, I’d swap it. Better yet, get one made by Delco (which was a reboxed Delphi last I saw a couple years ago) if that Standard brand wasn’t a Delphi to begin with.

 

[HoeLV]

What voltage is that downstream sensor sitting at?

It should be pretty steady and not oscillate like the upstream, but if it’s fixed below 26 mV it should trip a low voltage code P0157. Try swapping it with the other downstream sensor and see what it does.

For comparison, here is my son’s 98 after a cracked head (Bank 1) flooded the exhaust and locked the engine. Bank 1 downstream sensor implies that the catalyst isn’t doing anything productive. Bank 2 is steady. Whether it’s “too” steady is unknown to me, but it is a new converter, doesn’t trip a code and responded the same way after replacing the bank 2 downstream sensor. I think it’s ok.

Either way, the cause of any catalyst inefficiency would be the first thing to remedy.


To me, your issues started with 5 and 6 misfires that appear to have been resolved after the ignition work. Following the MPFI replacement, you got a #2 misfire that doesn’t look to be ignition or fuel pump related.

It’s easy to spend someone else’s time and money but that injector assembly seems a reasonable culprit. If it can be warrantied out, I’d swap it. Better yet, get one made by Delco (which was a reboxed Delphi last I saw a couple years ago) if that Standard brand wasn’t a Delphi to begin with.

It wasn't below, Bank 1 and 2 02 sensors both looked to be similar in readings while I was driving.

I'll have to go back to look at FT.

My plan is to remove the spider injection and take it back to be replaced by warranty. It has a "limited lifetime warranty" for whatever thats worth at O'Reilly's. Unfortunately it is the Standard Motor Products unit and not the Delphi. Hopefully unit 2 resolves the issue.

While doing that replacement, I am going to do the lower intake manifold gasket.

How much more work is it to do the valve cover gaskets? Should I look into doing that as well?

 

[east302]

You have to pull one cover to get the intake out (usually passenger) but driver side comes off just as easy once the a/c bracket is slid back - which you have to do anyways for the intake to clear.

That Felpro kit that I posted comes with both valve cover gaskets.

 

[HoeLV]

I forgot to come update this thread after swapping the spyder injection under warranty.

So, I ended up replacing the unit under warranty, surprisingly with no pushback from O'Reilly's. I took the first one out and brought it in. They pulled up the purchase record and grabbed the new one off the shelf. The biggest thing was they wanted the box it came in, which of course I didn't have, so I gave them the new one. While doing that swap, also did the lower intake gaskets which was definitely a good idea. While it was torn apart, ended up replacing the thermostat, PCV valve, radiator hoses and coolant flush.

What a difference. The misfire is gone, runs smooth as can be, better mileage, etc.

Then about 2 weeks later, I was sitting idling in the parking lot for a few mins and out of nowhere the truck shuts off. I try to restart it and nope. It would try and try to crank over but it wouldn't. After a couple hours of trying to figure it out, was able to determine the ignition coil module was done. Got that replaced and then a couple days later was having issues with keep a charge on the battery. It would output 14 amps and occasionally I would catch it down at 13 amps. Then would have a few mornings with a dead battery. Being 2.5 years old, went ahead and replaced it. Started a 200 mile road trip and 75 miles in, I see the voltage had dropped to 11.7. I was able to get to the next town and checked to see what was going on and the cable from alternator to battery and completely melted through. I am guessing it started to get weak and getting hot enough to melt through, explaining the poor charging and random dead battery.

Finally, after that it has been running good. Until last week got CEL and the P0430. I ran some cat cleaner through and replaced the bank 2 downstream O2 sensor and reset the code. It stayed off until yesterday and came back on. I have a feeling it will be time for a new catalytic converter soon.

Thanks again for all the help.

 

[east302]

I was wondering if you ever got that sorted out. Thanks for the update…sounds like it’s keeping you busy