I have been trouble shooting a problem on my '85 760 Turbo that has left me confused ever since it left me stranded miles from home.

The symptoms are:

1. Idle is low 500-700 RMP and not very stable. Car idles fine after throttle is pressed for a little while then will intermittently idle rough and low again.

2. Car will run for 10-15 minutes, then after shut off will not start again - engine sometime fires but barley ignites fuel and is similar to a car running out of gas. One can smell a gassy smell during this time. Engine might catch and then run with idle problem then cut out.

3. Sparkplugs show a rich running engine

What I have done:

1. Diagnosed Coolant Temp Sensor and it gives the correct reading.
2. Wire Harness has been patched up where required (have original wiring) but testing various engine sensors from the ECU (using volvo manual) says wirng is not an issue.
3. Distributor Cap removed and small black marks on points cleaned off
4. Oxygen Sensor diagnosed for voltage output .5 V is reading so I am assuming it is fine. CO was not tested.
5. Throttle body was cleaned.
6. Timing was checked and seems to be at 12 degrees on idling. When throttle is activated timing jumps to 20-30 degrees and maintains itself - timing change seems smooth but don't have enough experience to tell the difference if it was not smooth.
7. Fuel pumps are running
8. Fuel pressure regulator was replaced.
9. Injectors were diagnosed by sound and are all clicking away.

What I would like to know:

1. How does one test spark strength? How is the Coil diagnosed?
2. How is the distributor / cap diagnosed and when does this need to be replaced?
3. Can the fuel pump relay display intermittent problems that cut will reduce gas flow to the engine then return?
4. Any other tests I should do?


Thanks for any advice you guys my have and for reading this long post!

Set the Basic Idle Speed and Mixture. The procedure is in the 700/900 FAQ. That will cure your low warm idle speed.

If your O2 sensor stays at 0.5 volts after setting the Idle Mixture, it is bad. The O2 sensor voltage should vary from about 0.3 to 0.8 volts if I remember correctly. If it doesn't vary, it is bad. Try revving the engine while watching O2 sensor output.

Re-solder the Fuel Injection Relay. Having repaired about 40 of these relays, (if it is the original FI relay) I'm sure it has cracked solder joints which can strand you.
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john

Thanks John - I'll lool into the fuel relay but I think what I am getting is a rich fuel condition.

The 02 sensor maybe the culprit so I'll check the output while revving and see what happens.

Any idea on when to replace the rotor and cap? How to tell if one is getting enough spark?

Thanks again,

You could also have a bad AMM (Air Mass Meter). I would suspect it before the O2 sensor.

If the rotor and cap need replacing you will notice a miss under high engine load first, and then under moderate engine load.
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john

I have already swapped out the AMM with another good one with no changes to the problem. Pretty sure that is good.

The engine does feel like it misses - like a hesitation that sometimes happens.
There is spark at all cylinders and black plugs showing mixture is rich.

So I'm wondering if spark strength is measurable - maybe I'm not getting full ignition. Don't know if there is some device that measures spark length or something to indicate if the coil is functioning or if the contacts in the distributor are worn.

When I took the cap off there were black marks on the contact points I needed to clean off. Does that mean wear is occurring and the spark is jumping from the rotor to the points and I'm losing spark?

Thanks for all the suggestions. Much appreciated.

Have you removed all of the induction hoses, cleaned them, and inspected them inside and out. A rich condition often indicates an induction leak on a turbo car.
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john