All,
My 1998 S70 has just recently thrown a P0172B code, with a pending P0301B code, and from what I can tell while driving it, I notice nothing out of the ordinary.
The car was purchased in 2016 with around 125k to 130k on the clock. It is now reading 155k. I’ll have to check my records to verify for sure.
I’ve only visually checked all of the vacuum lines to date, nothing else. Before I get into what I plan to do, does anyone know how many drive cycles are needed to set the CEL once I’ve cleared it, if in fact I have not fixed the problem?
What I plan to check is as follow(s), hopefully least expensive to more expensive:
- Smoke the system to check for vacuum leaks, fix as required, (replaced the PCV system in 2016, so it should be good),
- Spray brake cleaner on the fuel injectors while the car is idling to see if I have a leak there, replace o-rings as necessary.
- Inspect the spark plugs, though I don’t think this is the problem as they were replaced after I purchased the car.
- Inspect and clean MAF with CRC MAF cleaner. Car does not stumble at idle, so I think I might be able to rule this out as a possible bad MAF, though I will clean it.
- Test current ECT and compare with new ECT, replace if bad. So a question here, how do I know if it’s bad? What resistance value or range should it have?
- Check for faulty Thermostat, flush system while it open because it’s time to flush it, and replace the thermostat if it’s bad. I don’t suspect this to be bad as its only 2 years old, but one never knows.
- Check fuel pressure, if in spec move on, if not, replace regulator with new one. What PSIs should I be seeing if the current regulator is operating correctly?
- Finally inspect, and test the O2 sensors, replace if bad. How do I go about testing these to determine if they are bad?
So does this sound like a good plan of attack? Have I left anything out that I should be looking at?
Thanks in advance,
Matt

Thought I had it with the bad ECTS, but NO!

I've replaced the O2 sensor, and no joy!

I've replaced the MAF, only joy there is that the P0300, P030X are now gone.

So I'm down to the following:
- Fuel pressure at the rail,
- Fuel pressure regulator,
- Fuel Dampener,
- Fuel pump,
- anything else that I might be missing????

A question I need an answer to is what can I safely pump the pressure regulator to so that if it is ok, that I don't damage it in the process of diagnosing the problem.


Thanks as always,

Matt

I have never figured out how to 'smoke' the intake manifold, as some of the valves are open and the air will leak out through the exhaust.

Check the hidden vacuum elbow next to cyl #1. The hardest to replace and see.

If the front O2 sensor is over 125K, then it is time to proactively change it anyway. Not terribly difficult, if you have a good 7/8 socket made for the sensor. The rear sensor usually lasts a very long time.

The ECT sensor can be checked with a multimeter. Unplug it and check the Ohms at various temperatures. Cold = 7300, hot = 300.

Your MAF should still be good, as should your fuel pressure.

Go ahead and check the spark plugs, clean them. If they are copper plugs, keep them, anything else, get new plugs.
--
Keeping it running is better than buying new

KlausC,

You stated as follow(s): "Check the hidden vacuum elbow next to cyl #1. The hardest to replace and see." I did check this and it is fine, and it should be as its part of the PCV system which was replaced in 2016, so as I stated it should be fine and is. This was proven out in the smoke test and brake cleaner sprayed on said elbow.

So here is what I've done tonight.

- smoked the system and found nothing,

- sprayed brake cleaner on all the injectors and vacuum elbows, nothing.

- measured resistance on new ECT and found the following:
Cool = 1800 Ohms, Hot (boiling water) = 170 Ohms, so this is what I need to compare the current one to, and these values make sense, engine cold, high resistance tells the ECU to dump lots of fuel into the engine, low resistance tells the ECU that the engine is now hot, therefore cut back on the fuel.

And the winner tonight is.... the current ECT Sensor that is in the car as I type.

So I finally checked the resistance on the one in the car. The cold reading was 0 Ohms, dead short, so this tells the ECU, hey the engine is hot, cut the fuel mixture back. So I started the car and let it warm up and then measured again. The hot reading was infinite Ohms, or completely open, therefore this reading is telling the ECU, hey the engine is cold, dump as much fuel into the engine to warm it up so we can reach closed loop mode.

Because of this, the O2 sensor(s) detect more fuel than air in the mixture and set the CEL.

So maybe tomorrow night, maybe Thursday night I'm going to flush the coolant system as its been 2 years since I did it last, and I like to flush both the brakes and the coolant system every 2 years if at all possible so that things continue to run smoothly.

I'll reset the CEL after I'm done, and drive it for a couple of days to see how things are doing.

As far as the O2 sensor goes, I'll put that on my list and hit it at the next oil change.

As always, thank you.

Matt
--
1989 - 245, 1990 - 245, 1991 - 245, and 1993 - 245

Good work! Check those plugs... They may be dirty from running rich.
--
Keeping it running is better than buying new