'87 760 (B230FT) Injector Test

I am understanding you have determined you have good pressure at the rail. Have you checked for spark? If that is missing, the Hall sensor may have died... without the signal from that, the injectors never fire.

I suspect the 16 ohm reading includes the ballast resistors or is for the non-turbo injectors. My B230FT injectors measure about 2.5 ohms. With just one injector disconnected I read about 5 ohms to ground on one side of the connector and about 7 ohms to ground on the other side.

Mike

On an YM87 2.7 Ohms is correct for blue top injectors (aluminum low resistance quick acting). If you were to measure the resisitance between the injector wire pairs at the control unit you would see ~4 Ohms since the resistance from the resistor pack in the turbo harness would be added in. If you get no flash from the power wire to the injector while cranking then either the computer has died, the harness is bad or there is no spark. If you have fuel pressure at the rail and the fuel pump runs while cranking then you have spark.

Bob

Thanks for the responses.

I have verified there is fuel in the rail. I believe there is spark because starter fluid in the air intake will cause the engine to start for an instant. I think the problem is that the injectors are not getting a pulse. I determined this by plugging a voltmeter into the back of an injector plug and watching for any sign of voltage when I crank the engine. here was none. Does this test make sense?

I have already checked what I could on the ECU using the Chilton information and according to the guidelines the system grounds, air mas meter and coolant temp sensor are okay. The throttle switch test failed at the full throttle position but passed at the idle position. I also checked the air mass meter at the meter itself. There was no mention of a check for injector control on the ECU.

User wrote:

Look for the injector resistor pack, it's on the inner fender near the front of the car. Verify no broken wires and clean the connections. Believe it or not, this part does not use waterproof terminals.

Also look for a black relay with 4 round pins on or near one of the shock towers. This relay supplies power to the injectors.

Thanks again for the help.

I believe I ohmed out the resistor pack a while back and it was okay but I will check it again. Is the black relay you are referring to the radio suppression relay? I encountered some confusion regarding this earlier. I have a black relay on the driver's side near the shock tower but I came to the conclusion after some research this is not a "feature" on the '87 turbos. Do you agree?

If not, the literature I encountered indicated that I should swap this with the electric fan relay but I could not find a second relay. Do you have any idea where I should look for the identical fan relay?

Some the diagrams I have seen include inline fuses for the injection system that are under the hood. I have not seens any references to these in trouble shooting tips so I have avoiding them. Any chance they could be the problem?

Mike F wrote:

YM87 only had the radio suppression (injector) relay under the hood by the PS reservoir bottle. The cooling fan relay was a five pin type in the central electrical panel behind the ashtray.

Bob

Right. And the suppression relay was something they added part way through the year, and as an free update (recall?) to ones (and 85 and 86 model years) that had already been sold. This is why it may not show in all literature and manuals.

This poorly named relay is called (by Volvo) the radio suppression relay. What is does is supply power directly from the battery to components that require pulsing (on-off) power - like the injectors. This isolates this "noise" from the supply to the radio, thus "suppressing" interference.

This is great info. Things are starting to make sense. I only have the relay by the driver side shock tower but it has the correct part number so unless there is another use for that relay I will assume it could be the culprit. Any suggestions on testing or should I just replace it? Any ideas on where I could find one?

Mike F wrote:

That relay sends power to the resistor pack. There's one wire at the resistor pack that is connected to all 4 resistors. The other 4 wires go to the injectors. The other wires at the injectors are grounded by the FI computer, which is what opens the fuel path. Check for power at the resistor pack.

The problem was the wire that inputs the voltage to the resistor pack was broken inside the plastic resistor pack connector. I found it when I went to clip a volt meter to the line to see if anything was coming out of the radio suppression relay. I picked up two spare resistor packs in good shape and a couple relays just in case at a salvage yard for $21. Replaced the resistor pack and used my original relay and it started right up.

Thanks for the all the help.

Mike F wrote: