'93 W124, 3.2 liter M104 - CE light, found 2 codes

[suginami]

I got the dreaded check engine light again today.

1993 W124, 3.2 liter M104 engine, about 138,000 miles.

I checked the LED display and got a #4 code and a #26 code.

#4 seems to be Air Injection Inoperative.
#26 is upshift delay switch-over valve open or shorted.

I was plagued with the #26 code until I changed the valve and cleaned out the vacuum line. I can't believe the valve could already have gone bad or the line could've plugged up again. The part can't be 6 months old.

Is #4 as obvious as it seems? Does it mean that the Air injection pump that runs for 45 seconds on cold start-up has broken?

Thanks in advance.

[suginami]

Anybody?

[suginami]

Feel free to jump in with some advice.

I cleared the codes and we'll see if they come on again.

FWIW, on cold start-up this morning, the air pump did come on and ran for about a minute and a half before shutting off. It's makes a lot of noise, but it always has.

I hope it's not the darned air pump, because Phil at PartsShop sells it for $967.51. I don't even want to know what the dealer charges.

Does anyone think perhaps the hot, hot weather confused the system and the pump didn't engage just once or twice?

I have this weird luck that the only parts that break on my car all cost about $1,000.

[MikeTangas]

Paul, check the vacuum line to the upshift delay valve, make sure it's connected, it might have slipped off.

If the pump is making noise, it could be on it's way out, but since they only run a short time it should continue to function for a while. It also has a vacuum line that has vacuum only when the engine is cold (through a thermo switch).

You just had the head worked on, is it possible some vacuum lines were errantlt routed or otherwise misconnected?

[Arthur Dalton]

AIR system :
There are 4 components to check on the system:
1-Pump w/clutch:
You know this is electrically OK cuz it comes on. [clutch engagement]
2-Switch Over Valve:
This is an electrically energized valve that allows engine intake vac to reach the AIR shut off valve. You know this is recieving an electical signal cuz it is wired in parallel with the pump clutch
[ which has power , so same for valve].
This SOV is located under the front cover at front of engine. It has a clear plastic vac. feed line from the intake. Check this for breaks, as they are common cuz the plastic hose dries up and cracks from eng. heat.
3- AIR shut off valve:
This valve is a gate between the pump output line and the eng. head. It is energized by the small vac. line coming from the SOV.
So, if you have vac at this line from the SOV when the pump comes on, the valve is suppose to open to let the pumped air continue on to the eng.
4- Check valve:
This is the last valve between the shut off valve and the engine. It is there to prevent pressure from engine going back to the system. This is a one way valve and is self operating according to pressure.
One should be able to blow through it in one direction only.

Any of these can cause a fault code if they are not operating.
[ clogged/no vac/bad valves/etc.
I doubt you have an electrical failure as the pump is coming on.
Could also be bad pump.
As one can see [ and I listed these components in order of air flow], the pump comes on---blows air to shut off valve[ which is opened by vac line from SOV]- ---air goes through shut off valve and the pressure forces check valve open --- air reaches engine to heat exhaust/lower emmissions.
Thats the general operation and will give you an idea of what to check.
Once you see it , this will become a lot less complicated than it sounds reading it...
My first check would be all vac lines , second would be to see if
you have vac at shut off valve when pump comes on [ a vac gauge is nice here]

PS Note*
For anyone reading this far, it is noted that the plastic vac line mentioned above is also the feed for the EGR SOV stacked together with the AIR SOV under the front cover .. so EGR faults can also be this same plastic line...

[suginami]

Thank you very much Mike and Arthur.

This gives me some things to check.

It's almost 9:00 p.m. here in the West Coast, and I just got done washing the car in preparation for the GTG at the part in Newport Beach tomorrow.