‘87 VDP No Start

XJ
1

Hi everyone,

I’m finally getting around to getting my ‘87 VDP started. It ran rough when I bought it a year ago. Put new air filter, spark plugs, HT wires, coil, and rotor in it and it died (LOL). Turned out to be the fuel pump. Now with a new pump and fuel filter installed it will not start.

I’ve followed much of the advice on this forum (thank you!) to try to get it started, especially from this thread:

-Confirmed all steps that CEI is working. I get a crisp blue spark at the plugs.

-I have 36 psi at the fuel rail.

-I do not have a NOID (going to Harbor Freight today), but used my test lamp to confirm power at the injectors. Hmmm, I should have cranked it to see if the test lamp goes off and on. Forgot to do that.

  • Important: I can get the car to run for 5-7 seconds if I undo and tap together the white and black wire on the inlet manifold/water rail like this guy does in the video:

Then it dies. I assume this is the trigger from the coil to the ECU to energize the fuel injectors. My guess is the amplifier is working in one side to fire the coil, but not the injectors? Thoughts?

Other issues, maybe related are:

1). I have to jump the fuel pump relay to get the pump to work (which makes me believe maybe the original one wasn’t bad in the first place).

2). The exterior lights used to work before it died. Now, they do not. Radio, interior lights, windows, etc. work.

3). Fuel Injection Wiring harness is very brittle. I will need to replace the harness. The Thermotine switch cover disintegrated when I touched it and I see cracks in the wires.

Anyway, could this be the ignition switch that’s causing all the symptoms or a short/ground issue somewhere else?

Thank you in advance for your help! I’d like to get her running again!

-Ray

2

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The white/black wire connects the ECU to coil neg, Ray…

This wire is powered with ign turned ‘on’ and in ‘crank’. With ign ‘on’ and disconnect/connect this connection you effectively send one trigger signal to the ECU to open the injectors once. This happens each time you turn ign on - and if there is fuel pressure at the rail, some fuel is injected…

However; dis- and reconnecting may also restore an iffy connection; after your ‘second’ start - the engine showed no signs of stopping…?

The ign amp triggers both the ignition system and the ECU - but on two independent wiring circuits. You may have perfect ignition, but signals are not getting to the ECU to trigger injection…

While cranking; the tacho should react if the ign amp is triggering. The plugs should spark and the injectors should operate - verified either by listening or the NOID at an injector flickering…

So the injectors should click when manipulating the white/black, confirming triggering and intact connections - but not much else…

Frank
xj6 85 Sov Europe (UK/NZ)
**

3

The ignition works as the engine runs, and the injectors inject. You can hear them clicking every other (third) time you make contact with that signal wire. Assumptions thus far are correct.
I would jump the fuel pump (at the relay on the bulkhead) and see if that makes it work. You did and it doesn’t help? Strange. It should cure the problem… My assumption would have been lack of fuel pump action: after it is powered briefly during cranking, it won’t keep running as it should and the engine dies.
When you have the ignition on and push the flap of the air flow meter in, does the pump run? There is a contact inside that might have broken. But with the sidelights and such, it can very well be the ignition switch. I don’t know the federal setup, but you‘d have to look into the S52 wiring diagram (pdfs via Google).
Rule out the amplifier for now, seems good, I bet on fuel pressure and something electrical.

Good luck, David

4

UPDATE 1/6/2019

Thank you Frank and David for the input. I’ve gone back through everything and confirmed the following:

  • measured fuel pump relay, main relay, and diode and all are functioning according to specs

  • measured the distributor reluctor and it’s within tolerance

  • fuel pump engages as it should when I slightly push in the MAF flap

  • Power is at the injectors and both brown/slate wires at the injector resistors

  • ECU has power at pin 10 and good grounds

  • ECU has power at pin 1 from the coil (Hmm, i should measure while cranking to see if it drops)

  • NOID confirmed no signal to injectors during cranking. The only way I could get the NOID to light was by cycling through the single wire along the water rail until the ECU got to that injector.

I replaced the HEI module and condenser inside the amplifier. At this point I think the ECU is working because when I “trick it” with the single wire, it fires an injector. That’s the only way I can get the car to run and it only runs for about 3 seconds. I think somewhere the signal to the ECU is failing. Even though it’s a new coil, I think that might be the culprit.

Thoughts regarding my logic? Any other suggestions?

Thank you,
Ray

5

Just swapped out the coil. No difference. I’m going to take the ECU to my Jag mechanic tomorrow. He was working on a few Series IIIs last week when I picked up my XJS. I’ll see if he’ll swap it out and see if it works in another XJ6. That way I can eliminate or verify the ECU as the culprit.

6

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The ign amplifier runs both shows, ignition and injection by ‘make/break’ of coil neg. The coil (ignition) and the ECU (injection) are independent of each other - both run by the ign amp by the coil neg connection…

The NOID can be used between coil neg and ground, between the ‘water rail’ connection and ground - and indeed at #1 connection at the ECU connector to ground. The reaction is the same; fully lit with ign ‘on’ and flickering while cranking - to be verified all along the white/black ECU connection; to eventually see where/if it is lost…

Unfortunately, for electronic reasons, the ‘coil/ground’ NOID application is not foolproof. It is therefor necessary to verify spark quality as well - using a spare spark plug. With proper sparking; the ing amp is likely working as it should - and the ECU is more tolerant to a quirky ign amp.

Be aware that using the NOID at the coil and at the injectors will not interfere with engine starting and running. You can keep them in place to monitor if the signal disappear. This is important to verify if the problem is loss of signal - or something else. The NOIDs can be used with everything connected up - just tapping to ground from the connectors…

Conventional use of NOID; across a disconnected injector plug - no light with ign ‘on’ and flickering during cranking.

Your logic is fair enough, but all injectors should fire simultaneously when triggered. The coil is immaterial for triggering the injectors - but of course rather important for spark quality…

Incidentally; as ign is turned ‘on’ the injector NOID should flash once. But in any case; the fuel rail must have pressure to inject fuel when the injectors opens…

It’s an odd situation - and one must ensure that one is barking up the right tree…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)
**

7

The injectors click all at once.
If the engine runs for a short time when you click the injectors a few times I’d suggest fuel pressure or leanness in general as next thing.

David