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Failing smog, waay too rich

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Jim Con
Posts: 3
Joined: Tue Jul 10, 2018 10:15 pm
Location: Aurora,co

Failing smog, waay too rich

Post by Jim Con » Tue Jul 10, 2018 10:50 pm

1986 635 auto 99,000 miles NA
Failed smog last year:
CO GPM 106.62 Failed
allowed 20.0

HC GPM 2.45 Passed
allowed 2.5

NOx GPM 1.48 Passed
allowed 4.5

First thing I did was new O2 sensor, then a different one still failing.

So far I have:
1.Replaced wires and distributor cap. Fine
2.Replaced coolant temp sensor, old one ohms out same as new one at different temps. Fine
3.Ohmed out cabin temp sensor.Fine
4.Lubed and checked idle control valve, vibrates at idle, opens and closes fine.
5.Plugged cold start sensor at fuel rail .
6.Have different AFM's, one I use as a base is out of friend's 86 635 ( never been opened ) his 635 runs fine.Have "mapped " one spare to correct voltages by adjusting potentiometer sweep arm to new carbon track and slightly adjusting sweep arm to read lower voltages.This has helped slightly.
7.Plugged in friend's ECU, no change.
8.Smoke test and seafoam treatment doesn't show any leaks.
9.Installed new correct sprk plugs, they go black and fluffy in minutes just like when I clean the old ones.
10.Installed new FPR, no change from old one.
11.Reference sensor and speed sensor ohm out correctly, if I switch them car doesn't start, so they seem to be working.
12.Have contact cleaned every connection found and have wire bushed all ground connections.

Introducing small air leak at manifold ( disco cabin temp sensor hose ) makes it idle higher 1100 and smoother.

TPS is a problem , linear voltage readings and ohm readings go in the wrong direction .
Idle speed is a rough 950 with the TPS connected, give it the gas and the tach will drop to about 700 and then rise to 950.
From my old carb tuning days this means too rich.

Idle speed is a rough 950 with the TPS disconnected, give it the gas and the tach will drop to about 700 and then rise to 950.
Apparently it makes no difference if the TPS is connected or not, this is at all RPMs.
Ohm test TPS disconnected
Idle ohms should be 2.0 actual is 4.2
Floored ohms should be 10 actual is .62

Voltage test
Idle volts should be .7 increasing to about 5.0 when floored with ignition ON and backprobe of connector.
Idle actual is 4.52 decreasing to .9 when floored.

Tests done on 2 different DMM's give same readings.

Really stuck on why I'm running rich.

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Brucey
6 Series Guru
Posts: 9835
Joined: Fri Apr 09, 2004 7:17 am
Location: Cambridge, UK

Re: Failing smog, waay too rich

Post by Brucey » Tue Jul 10, 2018 11:04 pm

TPS has switch contacts that
a) affect operation of ICV and
b) give the ECU a WOT signal

but potentiometer signal is only used by the gearbox ecu; it has nothing to do with the running of the engine.


One thing you have not mentioned is if you have checked the FPR compensation hose; this results in the fuel pressure being kept at 3.0bar (in most systems, 2.5bar in others, check you have the right one) w.r.t. the manifold pressure. If the compensation hose is missing or leaking the result is excessive fuel pressure at idle especially, enough to potentially send the fuelling out of range.

The other thing that could be fouling things up is a tiny blow on the exhaust. Amazingly this can suck air into the exhaust at idle, enough to fool the O2 sensor into thinking you need more fuel....

Another thing that is worth checking is that the CTS is actually connected to the ECU; unplugging it should make a difference, and if it doesn't you may have a break in the circuit. Compare readings at the sensor and via the harness. It isn't at all unusual for US-spec cars to develop a fault here because many of them were fitted with an inline resistor in the wiring harness; this commonly just breaks because it isn't strain-relieved in any way, being a bit of a lash up.

hth

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Jim Con
Posts: 3
Joined: Tue Jul 10, 2018 10:15 pm
Location: Aurora,co

Re: Failing smog, waay too rich

Post by Jim Con » Wed Jul 11, 2018 4:34 pm

Good points Brucey.

Car is shifting fine with or without TPS connected so maybe TPS is OK.

Have changed FPR, original was 3 bar so is new one.
FPR hose does have vacuum, when I squeeze it I don't hear any leaks anywhere.

No inline resistor on CTS.

Just went out and started it, idle went up 200 RPM when I discoed CTS.
Idle roughened when I discoed ICV so I think that's working.
Car speeds up slightly when I disco hose to FPR so I believe that is working by increasing fuel pressure.

Good point on exhaust ,after 18 months of rough running and occasional backfires the exhaust is louder and may need to be replaced.
Would a leak downstream from O2 sensor, maybe 5 ft downstream cause enough trouble to throw off O2 sensor?

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Brucey
6 Series Guru
Posts: 9835
Joined: Fri Apr 09, 2004 7:17 am
Location: Cambridge, UK

Re: Failing smog, waay too rich

Post by Brucey » Wed Jul 11, 2018 6:52 pm

I don't think a leak that far downstream of the O2 sensor would cause that kind of trouble, but it wouldn't take much of a leak upstream to do it. Unfortunately if there is hole anywhere in the exhaust, having someone put their hand over the tailpipes whilst you check for leaks upstream isn't going to work that well.

That the idle speed increases when the FPR compensation hose is disconnected is normal; it allows air to leak into the inlet manifold, bypassing the AFM, as well as increasing the fuel pressure. However it doesn't mean that there definitely isn't a leak into the inlet manifold from that hose or somewhere else.

Some other thoughts...

- have you checked the ATS value? ( the ATS is built into the AFM)
- have you checked to make sure you have a matched set of injection parts ? (FPR, injectors, AFM, ECU)
- have you checked to see that the AFM bypass screw is not wound in fully?
- have you checked the throttle body adjustment? (*)
- have you tried running the engine 'open loop'? (i.e. without the O2 sensor connected)

(*) there should be a 0.5mm (0.020") clearance between the throttle butterfly and the bore at idle. If there is less clearnace than this and the engine doesn't stall when the ICV is unplugged/blocked, this is a pretty good sign that there is an air leak somewhere. Depending on the position of an air leak it may cause rich running on some cylinders only e.g. if the O2 sensor 'sees' mostly gas from the lean-running cylinders for some reason.

hth

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Jim Con
Posts: 3
Joined: Tue Jul 10, 2018 10:15 pm
Location: Aurora,co

Re: Failing smog, waay too rich

Post by Jim Con » Thu Jul 12, 2018 7:03 pm

Will check ATS value
Injectors are rebuilt, all go black equally in minutes.
AFM is from identical car that idles at 750 and runs perfectly.I have not opened it or touched idle screw.
Need to check Throttle body adjustment.
Will check how it runs open loop.

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