Misfires and much more

[Maestrours]

Do you want me to drive the car a certain way and post a Vida report ?

[Maestrours]

Front O2 sensor seems to be indicating a perfect running engine. The rear tells another story. One of these two is likely wrong. Which?

Is it possible that both are right because cat is dead ?

[rrres]

I had issues with my fuel pump but it is solved, i think fuel pressure is ok.

...Ecm 261a long term fuel trim, too high...

I would test the fuel pressure again. It sounds to me like fuel delivery is not correct, causing the computer to add/trim more fuel at the injectors. The installed external check valve might be a culprit. I've read many posts by JRL promoting the miracle of the check valve, but there were a couple of posts where people had problems after the installation of the external check valve. There are other seals within the fuel pump assembly that can allow the fuel pressure to bleed down.

PS. a quick catalytic converter test is to use an IR thermometer. Point the thermometer as close as possible to the cat's inlet and measure temp. Do the same at the outlet. If the temps are about the same, then the cat is possibly damaged. A good working cat would have the outlet temperature much higher.

[Maestrours]

I had issues with my fuel pump but it is solved, i think fuel pressure is ok.

...Ecm 261a long term fuel trim, too high...

I would test the fuel pressure again. It sounds to me like fuel delivery is not correct, causing the computer to add/trim more fuel at the injectors. The installed external check valve might be a culprit. I've read many posts by JRL promoting the miracle of the check valve, but there were a couple of posts where people had problems after the installation of the external check valve. There are other seals within the fuel pump assembly that can allow the fuel pressure to bleed down.

PS. a quick catalytic converter test is to use an IR thermometer. Point the thermometer as close as possible to the cat's inlet and measure temp. Do the same at the outlet. If the temps are about the same, then the cat is possibly damaged. A good working cat would have the outlet temperature much higher.

Hi, thank you for this very informative answer. I'm receiving a fuel pressure tester this week so i'll have an answer about this point. I was thinking too that the external check valve might be a problem.

I'll figure out if I can have an IR Thermometer, good idea!

[Maestrours]

Hi,
Waiting to test fuel pressure, user @Jimmy57 said this in another topic:

"The rear sensor will go to its rich and lean extremes when there is load change on engine. <0.1 v when you let off throttle and >.75 v when you get into throttle or pull hills or other high load situations. When you are at steady load the rear sensor should be between 0.65 to 0.75 V. Idle is not important, you need to see what it does on level ground at steady throttle."

Here are my rear sensor data around 70mph at cruise control, then throttle of, then WOT:

Screenshot_20231119_214829_org.prowl.torque.jpg (139.39 KiB) Viewed 456 times

Rear sensor seems ok. If pressure ok I guess cat converter is dead ? I get P4801 code only in traffic jam, never under this screenshot conditions (highways, road with no traffic)
Problem is, in' my 00 xc i cannot find any replacement cat (8603014).

[scot850]

Are you allowed to use aftermarket catalytic converters in France? Here we cannot legally buy used catalytic converters from junkyards so they scrap and make money on them. We can buy and fit aftermarket units as we have no emissions testing here which can drive the preference to OE only.

Neil.

[Maestrours]

Are you allowed to use aftermarket catalytic converters in France? Here we cannot legally buy used catalytic converters from junkyards so they scrap and make money on them. We can buy and fit aftermarket units as we have no emissions testing here which can drive the preference to OE only.

Neil.

Only the emission testing really counts here. So if I mount aftermarket exhaust it is supposed to have a good cat conv. in it.

[wizechatmgr]

Front O2 sensor seems to be indicating a perfect running engine. The rear tells another story. One of these two is likely wrong. Which?

Is it possible that both are right because cat is dead ?

Perhaps. Follow that other poster's idea for checking the cat, seems like an interesting way of checking it. A lot cheaper and easier than a FLIR camera.

[Maestrours]

I had issues with my fuel pump but it is solved, i think fuel pressure is ok.

...Ecm 261a long term fuel trim, too high...

I would test the fuel pressure again. It sounds to me like fuel delivery is not correct, causing the computer to add/trim more fuel at the injectors. The installed external check valve might be a culprit. I've read many posts by JRL promoting the miracle of the check valve, but there were a couple of posts where people had problems after the installation of the external check valve. There are other seals within the fuel pump assembly that can allow the fuel pressure to bleed down.

Hi,
So I tested fuel pressure today. It is very stable, always around 52psi, at idle, at WOT, at 4500rpm...
Ecm 4801 is still coming back each time I delete it. So I guess it is the cat converter. I do not find any replacement piece.