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LH2.4 runs rich when engine get warmer

DennisvdB

DennisvdB

New member
Joined
Mar 13, 2011
Location
The Netherlands
I have a problem with my LH2.4 equipped '76 Volvo. It's now running a 3" MAF, a set of brown tops (cleaned and matched) and a 16T. When I start the car and let it idle, the A/F is around 13,5, briefly after that it starts to lean out (16,5 to 17). When the car reaches 60C Celsius, it goes back to A/F 13,5 and stays there. When the coolant temperature gauge reads 70C Celsius, the A/F starts to drop to around 12,5. From there until 80C Celsius the A/F has dropped to 10.0.
Aka full rich on idle.

The car has a new Bosch 3-wire 02 sensor, wired correctly. New plugs, wires and running wasted spark. New crank position sensor. Changed out the coolant temperature sensor (Bosch was in, bought a new Bosch), still the same result. Changed out the brown tops a few times with another set I have, still the same. Unplugged the 3" MAF, car stalled immediately so that's a good thing. The ECU-chip is original for now to try and find the damn problem. EZK chip is up to spec. ECU number ends with 984. Intake does not have a cold start injector.

What could be the solution to this problem?
 
Dennis,

How did it run with the stock MAF? Swap back the stock MAF and watch as the vehicle warms up. Are the fuel ratios the same?

Back probe the ECM at the coolant sensor and watch the voltage and coolant temp as the car warms up. Does the voltage at the ECM correspond to the coolant temp?
NOTE: you can find the voltage pin chart in the Volvo 2.4LH manual.

In my experience, Volvo grounds tend to get high resistance over time either by corroded cable and or dirty ground points). Make sure the grounds to the MAF and the ECM are clean (no excessive voltage drop) and secured.

While you are cleaning those grounds, make sure the main battery ground is also clean and does not have excessive voltage drop.

The same goes for the positive cable, make sure that you do not have more than .200V drop on any section of your positive cable.

The LH2.4 system is very voltage and ground sensitive because the ECM voltage at the coolant sensor is measured in millivolts. (as the coolant sensor warms up the voltage should increase)
 
Sbabbs, forgot to mention, it's a 012.

89740GLT: I'll try and get hold of a stock MAF since I don't have one.

I measured the volts of the coolant sensor as the car heated up, this corresponded with the correct values stated here:

http://www.swedishbricks.net/700900FAQ/EngineSensors1.html#Diagnosing ECT Failures

Grounds are as clean as can be, here's a picture of the engine a few weeks/months ago in build up.

dsc0023ai.jpg
 
Dennis,


I would really try the stock 016 mass air first. My wifes 940T has brown tops and a 016 mass air with a 15G and runs well with in the parameters that allow it to pass strict California smog.

If the mass air does not solve the problem;

Gonna throw out some ideas as a memory jogger.

Are all the basics set? ie Throttle switch setting, throttle plate set, fuel pressure, pcv system not sucking in any oil, iac working correctly, blow off valve not leaking, no stray jumper wires in the ECU or ICU, vacuum booster leaking, thermostat not stuck, engine ground strap installed, ground wire not installed over paint, charcoal can vents working correctly, charcoal can not loaded with fuel, radio suppression relay connections clean, no aftermarket wiring tagged into the stock sensor wires...

Are there any exhaust leaks?

Are there any Vacuum leaks?

Are both of the stock chips fully set in the socket?

I am going to keep thinking on this one and see if we can't come up with the fix.

That set up should be up and running because it is WAY too nice to be giving this kind of trouble.:nod:
 
Stock maf did not fix the problem, when on operating temperature the A/F is still 10. I'll try stock injectors and a different ECU...
 
engine temp sensor still OK?
thermostat working OK?
FPR working OK?
HighZ/LowZ injectors? using any ballast resistors?
 
Engine temp sensor is new as stated before. Thermostat working ok, as well as FPR. Lowz injectors with ballast resistors.

89740GLT, thanks for the tips.

Tried the 016 stock MAF, still the same (running rich when hot). Today I changed the 2 ground wires that are attached on the intake, to a solid ground on a different location that's absolutely working, because everything else connected to it works. Surprisingly, it did not run rich anymore on idle with the 016 MAF. Changed back to the 012 3" MAF, and at 85 degrees Celsius on idle the car has a steady 12,7 A/F now!
 
Yeah, it goes up and down, you're correct. It is 12,7 but chip is standard for now to try and find the problem. And ECU has some learning to do.
 
It should find 14.7 real soon or your injectors do not have the right size... Have you replaced the amm map in the chip?

Btw... Lh can be a real bitch when dealing with bad grounds...
 
Dennis,

You found a ground issue on your intake manifold. Good. Now we are getting somewhere.

Trace the rest of the grounds. You can also test the grounds by clipping a jumper wire to the negative cable and go around the engine touching the other ground points and noting how the engine runs.

I performed this test on my 740 and located a bad ECM and MAF ground. These two grounds are very important. If the ground is not clean the signals will be skewed and will cause the engine to run rich.

When I improved the ground with a jumper wire the engine idle would immediately smooth out. My voltage drop on those ground points went from .237V to .086V. (Yes that makes a difference)

The moral of my story, clean the ground for the Mass Air Meter and the ECM. (you already found a bad ground on your intake manifold)

I agree with Maddog. Keep the system as stock as possible for diagnostic purposes. Once the stock operation is restored should you attempt to add performance items.

Your idle still seems a little rich at 12.7 but better than 10. Make double sure that you do not have any vacuum leaks or that the carbon canister is not adding any extra fuel (pinching hoses and watching the A/F ratio helps here).

Check the exhaust for small exhaust leaks. Small leaks fool the O2 sensor.
* If you have a custom exhaust on your engine, make sure none of the welds closest to the O2 sensor are leaking. (I have had this happen to me)

:cool:
 
Dennis,

(ECM) Engine Control Module. - the module that controls the fuel. Usually located at the right kick panel.

I think Bosch calls it the ECU (Engine Control Unit)

Keep us posted.
 
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