I'm at my wits end.

Earl · Post by **Earl** » 13 Mar 2008, 12:48

I have an 88 740 GLE with only 145,000 miles that ran like a dream up till a month or so back . We had just made over a 3000 mile trip and the car was perfect .

A few weeks after the trip the wife calls one day saying the car will not crank .Fuel pump was bad so I replaced both fuel pumps and filters . A week later the car won't crank again....this time someone tells me the ECU has gone bad , so 400 bucks and 30 minutes later the car is running again .

A few weeks later the car quits running again ! I go back through everything and see that I'm getting fuel up to the injectors..I have the wife spin it over then and see that the injectors are not opening . So just today I run to the closest Volvo dealership and buy a relay, the Radio Suppressor Relay that operates the injectors . Lo and behold the things will still not open .

So I had the wife spin it over again and I checked with my little light to see if any current was coming up thro the wires that plug into the injectors...I get no current from either side .

Any suggestions besides setting the thing on fire ? I'm bout tapped out so am on a limited budget .

Post by **billofdurham** » 13 Mar 2008, 13:54

One of the first, and possibly cheapest, things to check is the engine coolant sensor. If it is giving out a wrong value the ECU will compensate accordingly.

Had you noticed a low or high reading on the temp gauge before the trouble?

Bill.

Earl · Post by **Earl** » 13 Mar 2008, 14:33

Temp was always normal Bill , never had a problem with it .

Post by **jonesg** » 13 Mar 2008, 19:04

The ground wires on the intake manifold are a bit notorious for losing good contact, although I don't know that would prevent the injectors from getting voltage. I'd probably look at that radio relay again, its plug and wiring.

I'd pull the codes , see whats going on.
It should indicate if theres a missing signal someplace.

Earl · Post by **Earl** » 14 Mar 2008, 08:12

Ground wires all check out fine , got them all nice and clean with good contact.

I'll see if I can find someone with the "tool" to check the codes . In the meantime I'm thinking of pulling the wires from the suppressor relay to the injectors and seeing if I can find a short or the likes , or does this seem like a likely cause ?

Post by **billofdurham** » 14 Mar 2008, 13:11

I'd probably look at that radio relay again, its plug and wiring.

That seems the next step as this is the one item that will definitely stop the injectors.

I'll see if I can find someone with the "tool" to check the codes

If there is such a thing i think it will be dealer only as the '88 model is not fitted with a self diagnostic unit.

Bill.

Earl · Post by **Earl** » 14 Mar 2008, 14:40

I've pulled wires . jiggled wires , and tapped wires all around the new radio relay and still the injectors will not open .

I'm not much when it comes to the electronics of an engine so I sure do hate to go to pulling wires out from everywhere.....but it looks like tomorrow I'll be marking some wires and where they go with masking tape and have a go .

Still not getting juice to the injectors . Should the relay make some sort of clicking sound when the key is turned ? I ask because it isn't....

Btw , the advice has been appreciated .

Post by **jonesg** » 14 Mar 2008, 14:47

No OBD is a bummer, arrgh

put a multimeter on the omjector relay plug , position it so you can see the needle and crank the engine over, does it get any power to it?
If it does you can try jumpering it to remove it from the circuit.

Try checking voltage in and voltage out, it could very well cause a voltage drop internally.

Earl · Post by **Earl** » 20 Mar 2008, 10:12

jonesg wrote: If it does you can try jumpering it to remove it from the circuit.

Not to sound stupid , but how would I do this ?

Also , the four wires that plug into the Radio Suppressor Relay , only the red wire has any current , and thats with key off , key on and also turning the engine over . The other three wire have no current at any time . Normal ?

Post by **billofdurham** » 20 Mar 2008, 13:25

The red wire will be 'hot' all the time as it runs direct from the battery to terminal 4 of the radio suppressor relay.

The other wires should be:

Blue/yellow to terminal 2. This goes off to the fuel pump relay.

Green/red to terminal 3. This connects to a green coming from the air control valve and then to the injectors.

Black to terminal 1. This goes to ground (earth).

The Green/red is the other side of the switch in the relay and should go hot when the ignition is switched on. The blue/yellow should also go hot when the ignition is switched on but it gets its power from the fuel pump relay.

Should the relay make some sort of clicking sound when the key is turned ?

There should be a click when the relay is first activated but it should not click continuously.

Make sure that the wires are connected to the correct terminals on the suppression relay. If it still does not work it could be that you have a bad relay. Even new relays can be faulty, especially if they have been roughly handled.

Bill.