240 lh2.4 Custom Exhaust

ljk346

Bought this 1990 240 a year ago, has a home made 3” exhaust and cam (VX3? Is that a cam?). It is an NA car, Lambda light has been on since I got it, smells very fuely, make pops and bangs on decel.

It’s mostly fine unless it’s left for more than a day or two without driving (or if it’s a cold morning), then it takes 5-10 minutes of cranking and backfiring before starting up and misfiring it’s nuts off.

In my limited experience with modified cars I am assuming the larger exhaust diameter is telling the O2 sensor that there is too much air in the exhaust, so the ECU is dumping heaps of fuel into the combustion chamber, making it hard to start when cold.

I’m just wondering if you guys agree with my diagnosis or not, and if I am right what are the solutions available?

Larger MAF to trick the ecu into thinking there’s more air in the intake? Adjustable fuel pressure regulator to limit the fuel to the rail? Chip/flash the ECU to recalibrate the O2 sensor?

Any advice I would appreciate.

ramrod

Good afternoon

Yes the VX3 is a cam from a 940 with B230FB engine, it’s decent, more lift for better airflow at the upper powerband without losing anything from the bottom

As for your problem, what code or codes are stored? Before overthinking things too much, you want to start with the basics. How long since an ignition overhaul? How does it drive when hot? Idle? Fuel consumption? Smoke? Yes a non responsive o2 sensor is possible, but you need to carry out testing before replacement of any component which you do not know for a fact is faulty. A bad o2 is only one of the many other possibilities you may find when testing.

ljk346

ramrod I have ordered an ignition kit from FCP Euro (Skandix Brand) which should cover all bases in terms of faulty parts (coil, leads, rotor cap, rotor, spark plugs)

Drives great when hot, with pops and bangs on deceleration and the fuel smell.

Haven’t checked codes but will reply again when I check them. Idles badly when cold, misfires a lot, sometimes dies. Idles fine hot, no misfires. Normally get 300 - 350km on a tank of 98 octane. No smoke.

ljk346

ramrod

checked the codes today after driving for around 30 minutes getting the engine up to temp

2: 123 & 212

6: 224

Ignition kit arrived today so will be installing that shortly

Major Ledfoot

ljk346 - Does your speedo work? (LH 2.4 relies on a VSS to cut off injection on throttle over-run).

ljk346

Major Ledfoot yes it does work

ramrod

Install the ignition parts then test again.

You’ll know by the condition of the old ones if they’re worn

carnut222

Have you checked the fuel pressure and fuel pressure regulator diaphragm? Is the ECU temp sensor OK? Check resistance values.

ljk346

Ok so it has been a week since I installed the ignition kit from FCP Euro and here is my report. (new coil, spark plugs, coil and distributor leads, distributor rotor and distributor cap).

Day 0 (day the parts were installed)

Lambda light OFF

Starts up great, idles great, everything is good. No pops and bangs even when motor has been brought up to temp.

Day 1-7

Lambda light ON

Still starts up great on cold mornings, occasional misfire on sudden throttle depression at low rpm’s, even after reaching operating temperature.

Checked codes online to find that the Engine Coolant Temperature (ECT) code (signal missing or faulty) had been listed twice as well as an O2 sensor fault (signal missing or incorrect).

Checked the resistance on the ECT and found it was an open loop, no continuity or resistance value. It also has a bit of oil grime on the sensor which wouldn’t help. This is the ECT sensor correct? Under the intake manifold?

Image description

Also these are the spark plugs I took out when doing the ignition kit.

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1 looked rich, 2 and 3 ok, 4 looked oily and rich.

Cylinder 4 (furthest right) may have picked up some of that grime due to me not being able to see the placement well on that cylinder

carnut222

No, that's the knock sensor. The engine coolant temp sensor is about between cylinder 3 and 4 inlet manifold runners and is screwed into the cylinder head. The plug sticks straight out of the sensor, not at a right angle like your knock sensor shown in the pic.

carnut222

Also, check this out - info about LH2.4 ECU coolant temp sensor.

https://www.240turbo.com/volvo240mods.html#LH24tempsensor

ljk346

Update

I ordered the Bosch Brand ECT sensor from a bloke on Ebay and fitted it this week (PN. 0 280 130 032)

Before I installed the sensor I tested it to compare with the sensor that was removed from the car.

Symptoms with the old sensor:

Hard to start on cold mornings
Lamba light on dash
Code 123 (ECT Signal bad), Code 212 (O2 Sensor signal bad), 224 (ECT Signal bad)
Temperature gauge on dash never got onto the scale, showed cold all the time (it moved but never git anywhere near the middle to show operating temperature).

After installing the new sensor:

Hard to start on REALLY cold mornings (5*c or less), 5 cranks or so on a regular cold morning (~ 10*c or more)
Lambda light on dash
Code 123 (ECT signal bad), Code 224 (ECT signal bad)
Temperature on dash gets to about 1/4 of the gauge at operating temperature

Sensor Tests:

Old sensor at room temp [ Open Loop / Too Much Resistance ]

Old sensor in boiling water [ 22,000 - 28,000 ohms, jumped around a lot, never settled ]
New sensor at room temp [ 20,000 ohms ]

New sensor in boiling water [ settled at 750 ohms ]

Referring to Carnut222's handy link: carnut222, looks like the sensor I got was bad or not the right thing, the graph showing temperature and resistance values is a lot different to my new Bosch sensor.