[Trevor]

First post-holiday update. Sorry for the delay

Not a problem and as expected due to the festive season. LOL

In all of this I hope that you have a printed copy of the wiring diagram so while actually on the job, you can trace and understand what is involved.

1. Yes, I meant the modulator. The continuity check consisted of opening the modulator and checking that each plug ping (four in total) beeped when touching the solder point on the circuit board.

OK. You tested for faulty solder joints between the pins and the circuit board. Worthwhile as automatic wave soldering often misses connections to substantial components requiring extra heat.

2. I checked both. With everything disconnected as well as attached to the car & bracket.

My question was:-
 You also advise "I tested the ground on the bracket holding both the fuel control module and the fuel resistor". Was/is the metal modulator/resistor assembly still hanging unmounted or is it now bolted in place and solidly connected to ground ?

You advise that the bracket was attached to the car but I repeat, was the bracket solidly connected to ground ? Also refer (3) below.

3. Unlikely as its at the front of the car by the engine while all the fuel components (modulator and resistor) are in the trunk.

My question (3) was:-
 You advise " I have not yet gone under the car to inspect where this part "dropped" from but you just added to my list of items that I can not explain. Could this item be involved in the grounding and have become detached when you removed the modulator/resistor assembly ?

Everything involved here is unlikely, therefore only positive evidence can be considered. I repeat, could this item be involved in the grounding and have become detached when you removed the modulator/resistor assembly ?

Was, or was not, the bracket solidly connected to ground ? Also now refer (2) above and (5) below.

4. I am not sure how to actually perform that check.

My question (4) was:-
 Have you at any time checked the original resistor for a short circuit between its plug connections and its metal case which should become grounded ? I keep pressing for this information for a good reason.

A short circuit constitutes an unwanted circuit and a connection which should not be taking place and as a result comprises a fault condition. Therefore you check the resistor for possible continuity between its normal connections and its outer mounting case. It is important that the plug and therefore all external connections are removed during the test. Check with an ohmmeter set for a high a resistance in order to show any possible connection between either and both plug pins and the case. You are testing for a possible high resistance rather than a low resistance as when checking for faulty continuity.

You are testing for possible continuity or even partial continuity, between the inner resistor element and its case, as this would ground the pump and cause it to run continuously unmodulated at full speed. Even if the short circuit is of high resistance this can change as a result of heat during its operation. It would be preferable to use a proper insulation tester operating at an increased voltage, but in this instance an ohmmeter will suffice.

I also wanted to mention with more testing:
There is continuity between the positive side (as labeled on the plug) on the resistor and the other on the bracket.
There is continuity between the resistor pin and the corresponding modulator pin

I am unable to reconcile your reference to “corresponding” pins when a four pin and a two pin connector is uninvolved, particularly as different pin numbers are connected. However I will presume that with the interconnecting wring tested unplugged, that this is providing correct continuity.

(5) I now present a further important test. Note previous question (2) and refer to the diagram you have posted. Make very sure that when everything is bolted in place but with both plugs disconnected, that there is a solid ground connection to resistor plug pin (1) and also modulator plug pin (2). Test against several body points for good measure. The diagram shows the ground point which must be proven to be reliable.

P.S.

Further possibilities can be taken into account, but only after all the suggested tests have been completed and finalised.

If and when the resistor is removed, the modulator will switch the total current delivered to the pump motor and which then involves a high inrush on start up. It could be that the modulator output transistor is not capable of switching this rather nasty inductive load and therefore could fail, in which event the pump motor would never run at full speed.

One would expect the designers to have taken this possibility into account, but in fact they may have not done so. In which case experimenting by removing the resistor as has been reported, could have damaged all of the alternative modulators being used during testing.

Testing the modulators as individual units is not that difficult for someone with electronic knowledge, but otherwise there is the danger in destroying the driver transistor, particularly as the trigger voltage is unknown and it is likely that the input is simply switched to ground. Furthermore the illustration in the wiring diagram is probably figurative rather than exact.

An obvious crude test test will involve removing both monitor and resistor plugs and the bridging the resistor plug so that the pump motor runs continuously at full speed and then observing the pump and engine response. It is obvious that fuel pressure testing would disclose a lot but is not feasible under the circumstances.

Difficult one to sort and it will surely take until the end of the year, but patience will win the day. LOL