I'm helping a friend with his 1986 Volvo 240 Turbo, B230FT with the EZ117K. It will not idle and has no power, if we keep pumping the throttle, we can get it to run - barely. The history was he was driving along just fine when it suddenly developed this problem, he was barely able to drive it home at 30 MPH wide open throttle.

I Checked the following: Fuel: I put a gauge in a Tee in the fuel rail and energised the fuel pump relay by jumping 87/2 to 30. The rail regulates at 43 psi and varies when running up to 50 psi. I performed a volumn test, I ran the regulator output hose into a graduated container and had > 1.1 liter in 30 sec.

Exhaust: We checked for exhaust back pressure in case the catalytic converter was blocked, there is an exhaust plug just after the turbo and could not measure any backpressure - could there be a plug in the exhause upstream from the turbo?

ECM: thermal sensor measured at LH jetronic (LHJ) unit pin 2 to gnd. = 1.86kOhms at 70 deg. F, Mass Air Flow (MAF) Sensor at MAF pin 1 to 5 = 13 Volts with key on, Pin 2 to 3 = 3.7 Ohms, Pin 2 to 3 running = 2.1Volts to 2.6 Volts. Measured MAF at LHJ unit pin 6 to pin 7 = 3.7 Ohms, MAF @ LHJ unit pin 6 to pin 7 = 1.13Volts to 2.5 Volts, pin 6 to 14 = 1.52Volts, and pin 6 to 14 = 283 Ohms, Lambde Sensor at LHJ unit pin 20 to pin 25 with oscilloscope = .50Volts engine running, Throttle position switch at LHJ unit pin 3 to gnd. 0Volts to 5Volts pedal depressed.

Ignition: Coil terminals 1 to 15 = 0.70 Ohms, Terminals 1 and HT term.= 7.27 kOhms, Timing = 10 to 20 deg. BTDC when running, Oscilloscope measurements: Ignition Control Module pin 17 = 12 Volt pulse to gnd 6.5mSec low, 14mSec. , Ignition Control Module pin 24 = 5 Volts Peak to Peak low for 11.5mSec, high for 25 mSec., Ignition Control Module pin 16 = 5 Volt Peak to Peak low for 19.5 mSec, high for 8.5 mSec., Power Stage Module pin 1 = a typical ignition primary waveform 1.6mSec. 0 Volts, 0.8 mSec 12 Volts, coil fires spark discharges 0.5mSec, coil dwells for 4.4mSec then repeats, LHJ unit pin 13 = 13 Volts Peak To Peak 3.5 mSec low, 37 mSec High. I get a solid spark out of the coil, it will jump 3/4" and looks blue. We check for intake leaks everywhere, no obvious visual vacuum leaks. I am stumped! What failures - if any - can occur in the turbo to cause this symptom, I'm new to turbos.

Could the turbo bypass valve be stuck closed or the waste gate be stuck and cause enough boost at low rpm to engage the overpressure switch?


I really want to help this guy out, any ideas???

 

None of the induction hoses have any holes in them do they?
Try unplugging the mass flow sensor and see if the car idles.It won't run good over idle but should good if it is bad.

Have you tried cleaning the idle motor and made sure it is not hung up?

Make sure the timing belt didn't jump a tooth or two.

 

Thanks for your reply. I checked the timing with a timing light, it was between 10 and 20 Deg. BTDC. If the timing belt skipped a tooth, would the timing change?

As for the idle air valve, it was my impression if the throttle was opened, the air from the idle valve would be dwarfted by the throttle valve. If it was the idle air valve, wouldn't it just run bad at idle and be fine at open throttle?

I will check the air mass flow sensor as you indicated tonight when I get home from work. Again, I thank you for your input, I put 5 hours in so far with all the o'scope measurements and I'm frustrated.

Is there any turbo failure like the waste gate or bypass malfunction that can produce these symptoms? I have a digital sampling scope and it needs to be specifically set up to look for missing pulses which it was not. Is it possible there is a turbo malfunction causing too much boost at idle or off idle to trigger the over-boost sensor? This would shut down the fuel pump relay and the ijectors won't fire - this would not show up on the fuel pressure gauge as it will stay pressurized for awhile.

 

If it jumps time I don't think it will show up with the light.

You can put vaccum on the waste gate valve and check for proper operation.Does the car have a boost guage?

Im gonna see if I can think of anything else.

 

Got it! It was the Air Mass Flow Sensor - disconnected it and it would idle. Went to a local Volvo service shop locally, "VOLPAR", and purchased a used sensor for $190.00 and the car is fixed!

Is there any way to electrically determine the Air Mass Flow Sensor condition?

It was my understanding the distributor was driven by the camshaft, if the camshaft skipped a tooth on the timing belt, wouldn't it show up on the timing light?

I love learning from these experiences, I will remember this exercise for awhile.

Thanks for you assistance, it is gratifying to finally resolve this and we didn't replace multiple expensive components shot-gunning the problem.

 

Im glad you got it fixed.Most people don't use a timing light on these cars.The dist. should be run off the counter balance shaft on that car.Unless the engine was changed out and the dist. is in the back of the head.Then it might not show up as well.

Also depending on which balancer you have they will also spin and give the wrong timing readings.