Hi all,

Some of you may have followed my thread "her majesty the XJ8 is not starting". Thanks to great support and tips on this forum, I was able to restore compression and get her started again. That was a great releif. I had a bunch of codes show up pretty muc immediately. I was kind of expecting that. But after driving her for a good few miles now, she's still driving rough and 4 codes remaining: those of my HO2 sensors (P0031, P0037, P0051 and P0057). She starts fine, idles fine. But stutters a lot on acceleration, and feels like she seriously lost power.

Any thoughts here? I am assuming events are related, but who knows.

Of course, I am now reaching the deadline to get her inspected to get new tag. Always something ;-)

Cheers

 

Did you look up the codes using this site; they seem to give a good explanation of error codes and solutions.

http://www.permoveo.ltd.uk/tabid/122...r/Default.aspx

It seems strange that all 4 sensors have failed at the same time. I would suspect the fuse, (if any), the relay, water in a connection.

This is from the GMC forums, but has some good info on checking sensor functions

Catalyst System Efficiency Below Threshold (Bank 2) - GMC Forums

 

I would erase the codes, and do the "hard reset". Start from scratch, and let her throw the new codes (if any).

 

Thank you both. Danielsand, I had reset the codes with my reader but they pretty much came right back on. As to the "hard reset", is that disconnecting the battery and touching + / - wires together?

Do any of you think that the oil burned in the cylinders after my 'cinlinder wash' issue had the "contaminated" exhaust emission to clog the sensors in some fashion and therefore sending wrong info to ECM?

I switched around the relay this AM, and checked the fuse again. No change.

She's still running rough, doesn't like accelerations. Starts and idles fine.

Cheers

 

"Running rough" and "idling fine" is mutually exclusive. If she idles fine, I would check the fuel delivery system (all of it), and pull the plugs (again!) and inspect them. After that, I would force her to a drive, and get her up to operating temp under load (maybe with a back up vehicle behind, in case she decides to quit).

I don't think there is any damage there. Something is clogged, and/or oil got into something that doesn't like the oil. Running it with some clean gas (and a good injector cleaner), might just be a ticket.

 

Thanks again for all the valuable input. The clean gas and additive was the first thing done earlier in the week and made no difference unfortunately. Fuel delivery does seem to be the issue though. I think. Discovered today a loud suction noise at the throttle body, when accelerating. I was able to stall it a few times. The rpm slows before to pickup suddenly, while suction noise is heard.
All seems well sealed all around the intake, and thoughts then were not enough gas injected at time of acceleration. Electronic? Do the sensors send wrong message to ECM for fuel delivery? Or are the sensors telling me my engine is running on a bad mixture? At a loss at the moment !?!

Thx

 

Hi blue

Does your code reader show things like Fuel Trim and the voltage/current of the O2 sensors?

If it does post some values and if possible at different rpm and loads, if the O2 voltage (at least it is voltage on my 98) doesn't oscillate between 200 and 800mV either the sensors or its supply is suspect.
If it does, check your fuel trims, are they crazy positive or negative?
Usually the answer is buried in there somewhere.

Cheers

Lincoln

 

Lincoln, no I don't have such reader. Any suggestion of a reader that takes care of that? Curious to what the answer becomes depending on the result(s) ? What would (bad) reading(s) mean in this case?

Cheers

 

Sorry - I re-read your note and perhaps you answered me already. What I mean is what would I be in for, fora fix? New sensors? New fuel pump?

 

It's kind of a question which part is giving bad readings.

I use a PLX Kiwi and an I phone, but there are much cheaper versions out there.

I'd argue if your O2 sensors are oscillating as they should, then they are not broken or coated with oil.
But without seeing some values it's hard to know.

I wish I could tell you, change X Y or Z and you'll be fine, but it's not that easy.

Do you know anyone with a code reader that gets fuel trims?

 

Actually reading the diagnostics help in fredd60's first link, I think the first thing to do is to verify 12V at the heated O2 sensor in front of the Cat.
The failure code says this is not drawing enough current, meaning one of 2 things
1) no voltage
2) infinite resistance (ie broken O2 sensor)

Lincoln

 

Well.... the V8 is back to (expected) performance! I am not entirely sure of what brought me to this point, but it's somewhere between last night driving back home and feeling kind of a "backfire" in the exhaust (after stepping on it) and this morning cleaning the MAF sensor with some CRC cleaner AND sealing (with additional gook) the air intake seal at the top of the throttle. Driving in to the office this morning, she gave me the best power since I ownerd her (1st anniversary)!! Now, I still have my HO2 codes come up (check engine light). Erased them twice already but come right back up.

Cheers

 

Glad to report I found my HO2 codes trouble.... just the fuse!! Well, need to add some explanation as this was the obvious first part that was checked... when I checked and tested all fuses, I noticed from the diagram I had some position were "unused". So ok, unused so who cares, and in some instance a fuse was there, sometimes not. I had removed all the "unused" slots. When I eventually got the engine running again (see thread), I thought "better get all those supposedly unused slots fuses back, never know". When I kept getting the HO2 codes come up, I was thinking that my problem was not there. Well sure enough, it was. In a last swing before ordering new HO2 sensors last night, I went ahead and test all fuses again... BINGO - one was bad. Position 11 in the engine management fuse box. Diagram says "unused". Replaced with a good fuse, codes went away !!!! Guess it was used after all. So seems like I need to toss my diagram or find out about possible updates made to my model in 2001.... Time to go to take the NC State inspection ;-)