Timing belt Volvo 740 200k miles.

[Retired MVS Contributor]

When was the last time that the distributor cap, rotor and plug wires were replaced? A bad plug wire can cause a misfire at the RPM that you mentioned.

+1 on lummert's post...If the wires are old, I would replace them...Check the inside of the distributor cap for hairline cracks, moisture and carbon tracking and the rotor for burning at the center post where it contacts the cap...

Glad you got your money back...A lot of automotive supply houses will not refund on electrical parts because it is easy to damage them if you mess up while installing...

The fuel injection relay is located on the pull-out tray behind the ash tray...It is the tall relay on the extreme left in the second row...The overdrive relay is in the same row and is on the extreme right...The covers on the relays can be popped off by gently prying them loose from the tabs on the sides of the base...

With the fault returning for the speed sensor, you need to check the wiring from the control unit to the sensor...Replacement is the best option, but you have already done that...However, I would not assume that the sensor is OK and I would replace with OEM...If that sensor is bad, it could cause the symptoms you are getting in highway cruise, and if it were totally wiped, the car would not run at all...

If you want to get into testing it, you will need to access the control unit...(ECU)...It is above the drivers knees behind the upper knee well panel...Disconnect the connector and connect your ohm meter between pins 10 and 23...It should read (dependng on temperature) somewhere between 200 and 300 ohms...

Jerry

[dunamis]

thanks lummert and jerrymcc,

I'll try my hand at testing the ECU. You know, i replaced this with used unit already and issue did not resolve.

I went to junk yard and tried a used distributor unit as well, but that did not fix issue. I have thought of replacing the entire distributor system will a new one but the unit is over $300. :{

But, regarding the distributor: I replaced the cap(new), rotor(new), and spark plug wires(all new also) last week and issue still persists. BTW the vehicle will turn off, just shut down, intermittently at high speeds, usually above 40 mph. Don't know if this is related.

[lummert]

One more suggestion. Do you have access to a good power stage (ignition module)? It is easy to swap the power stage, but I wouldn't go out and buy a new one just to test this theory.

[dunamis]

thanks lummert,

Question, if the ignition module is faulty will the vehicle still start and a t least run still? Or, would it completely not run at all?Thanks.

[Retired MVS Contributor]

Any electrical part can fail completely, or, become intermittent...Intermittent operation is the most frustrating, it is difficult to find...

The power stage that lummert mentioned is not used on the Rex 1 (Bendix) system which I believe you have...If you have the Bosch system, the power stage lummert mentioned is inside of the left front fender and definitely is a possible culprit...The air cleaner has to be removed to access it...In the Bosch system there will be a standard round ignition coil over on the firewall near the right hood hinge...

If you have the Bendix system, the combination ignition coil/power unit is a large, black, finned unit mounted mid engine near the left fender and has the high voltage ignition cable coming out of it and going to the distributor...

Another thing you might try...There are two identical relays mounted on the coolant reservoir bracket...One is for the auxilliary electric fan in front of the radiator, and the other is the radio interference relay...The radio interference relay isolates the fuel injection system from the rest of the vehicle's wiring so that strong broadcast radio signals in the area will not knock out the fuel injection system...Since they are identical, you can switch them as a test...Maybe you can just switch the cable connectors without removing the relays...

Jerry

[91volvo740]

Hey, I just joined the forum today, researching my own problems. Regarding your intermittent over drive, I had the same problem and it was resolved by replacing the overdrive relay, located with all the other relays, behind the ash tray. Might want to give that a try once you get the car going.

[dunamis]

thanks 91volvo740, i did isolate the over drive issue to the relay and took care of that issue there.

thanks jerrymcc, I will try your suggestion and switch the relays. I will run to the junk yard and pull a 'power stage', too expensive to buy at this point.

***Questions:

1. is the distributor of a Bendix system vehicle interchangeable with the Bosch system?
2. can i disconnect the main vehicle computer to try a used main computer for this vehicle? a 'consultant at a volvo dealer said that if i disconnect the main computer, it will need to be reprogrammed again and only the dealer can dot it.

[lummert]

1: Make sure that the distributor comes from the correct year. A distributor for a car with LH 2.2 will not be the same as for LH 2.4. The same distributor is used on these cars:
89-92 740 B230F
90-92 740 B230FT
90 760 B230FT
91-95 940 B230F & B230FT

2: Sounds like someone doesn't know what they're talking about, if I'm not mistaken.

[dunamis]

thanks lummert,

can you elaborate on this info:

"A distributor for a car with LH 2.2 will not be the same as for LH 2.4. The same distributor is used on these cars:
89-92 740 B230F
90-92 740 B230FT
90 760 B230FT"

How do i check if my vehicle or distributor is an LH 2.2 or LH 2.4?

[lummert]

LH 2.2 uses a hall sensor in the distributor and has a plug to connect to the wiring harness, LH 2.4 uses an impulse sensor that reads the flywheel speed and doesn't have this plug.