It's a pulsation dampener. Same idea is used in big compressor packages for moving natural gas down pipelines, it smooths out the pulses from the pistons. There is nothing inside it, the expansion allows any pulses to die out and smooths the signal to the ECU

It's a Ford part, I have seen them in the junkyard on 80's Mustangs. I'm sure other Fords have them too.

 

No updates because, until today, the problem has not occurred again. My jiggle test of under hood wires revealed nothing and, FWIW, removing the vacuum damper thingy didn't make any difference.

Today it stalled several times but the previous condition of accelerating hard and then releasing the throttle was not part of the picture. It simply stalled while motoring along. Click into "N", restart, continue motoring.

However two new clues have developed.

Several times when starting the engine the speedo needle has swung around wildly and the trip computer goes nuts ....both signs of voltage drop. I have an idea where the problem might be.

More in a day or two

Cheers
DD

 

That sounds like a bad ground to me.

 

Does this mean that the other gauges Tacho etc do not swing wildly? Because don't all the gauges run from the same fuse, I know in the XJS they do. The only thing common to the Speedo and TC other than 12V is the VSS.

To me this sounds more like a noise issue, a spike on the VSS maybe. If this is the case then it could possibly be ignition noise induced into the white wire or even the 12 volts causing the ECU to stop injecting fuel. Thinking out loud here........

 

Entirely plausible. if that's the case I'll be disappointed because I was rather intent on pre-emptively correctly any grounding problems during the conversion process.

But....

I'm not so sure about voltage supply. In the back of my mind I have a nagging suspicion about the stack-up of B+ wires on the RH firewall junction post. I'm thinking it was something I was unhappy with and was gonna go back and take another look at....but forgot.

I'll know more in a day or two.

Cheers
DD

 

Correct.

But past experience has proven to me that when an electric speedo go wonkers when the starting the engine it's a lack of voltage.

Cheers
DD

 

I hoping for something less esoteric

Cheers
DD

 

Less esoteric? For one of our wizards, Doug Dwyer?

Hi Doug. I thought the trigger input for the ECU (Lucas EFI) was derived from CP sensor . . . also for tacho, which you reported in post #1 fell instantly to zero despite engine spinning down as it stalled out. As you know, these sensors have been known occasionally to act weird, totally fail or even disintegrate. Is it possible that a rapid change in engine vibration on decel is being transferred to sensor, thus upsetting the ECU trigger required for both fuel and tacho simultaneously to maintain, and indicate, the required idle state.

Perhaps the speedo thing is a red herring, or at least a misleadingly disconnected issue. Anyway mate, at your breakneck speeds, an accurate speedo is a thing of redundant information . . . LOL.

Cheers,

Ken

 

No crankshaft position sensor on a Lucas car. It gets the trigger for the ECU from the ignition module.

Speedo gets it's signal from the transducer on the transmission for distance info, and a signal from the ECU for fuel.

 

Doug
Have you swapped in another amplifier to see if it made any difference?
Greg

 

No, haven't swapped the amp...or the coil. It might come down to that, but we'll see.

The amp has a new AC Delco module already, and the coil is new...both done during the conversion... so they're further down on my list of possible culprits.

Cheers and thanks

Doug

 

Doug
FWIW I had about 2 years of intermittent funny starting issues, did various things which certainly improved but did not entirely eliminate them. Including new module in the amp etc etc. New amp fixed them.
Greg

 

Well.......

I found two suspicious things.

The main ground (battery to RH fender well) was slightly loose and the nut on the RH "+" post was slightly loose. By 'slightly' I mean it took a half-turn to tighten 'em up. However, prior to tightening them I gave 'em a wiggle test with the engine running and nothing bad happened. I'm not very confident that I've fixed anything.

Feeling a bit ashamed that these two critical nuts were not fully tightened. When I installed the main fuel injection harness really I goofed up. The harness branches off in several directions and I had the harness oriented incorrectly. All the branches were pointed in the wrong direction. Unfortunately I discovered this way too late, after I had already buttoned up the interior---seat, carpets, console, etc. To re-orient the harness properly I'd have to take everything apart again to remove all the harness anchors so the harness can be flopped over 180º. I'm here to to ya....that ain't happenin' ! Anyhow, I had to undo the wiring at the junction post and surrounding areas several times to make everything work. Obviously I forgot to properly tighten everything last time. Grrrr.

Drove 83 miles so far today without so much as a hiccup. I'd be tickled, of course, if whatever is faulty would simply fail outright and completely.

Cheers
DD

 

I had a car that I pulled out of winter storage and when I put the battery in it I didn't have the right wrench to tighten up the terminals. So I just pushed it on and it started and ran fine. I meant to tighten up the terminal when I got home, but forgot.

On the next major road trip I stopped for gas and the car wouldn't restart. Tried all sorts of things until I noticed the battery terminal was loose. I checked the trip computer and it was showing about 12 km less than I should have recorded, as it's a route I've driven many times and always fill up at the same station. Seemed like the terminal would bounce off the battery over bumps and than make contact again and the trip computer won't record that bit of distance until it got power again.

So it's possible the loose connections are causing you grief.

 

There is a good chance this will fix the problem.

Bad connections on high power terminals can cause all sorts of weird faults. As the current draw goes up the resistance in the bad connection causes a voltage drop and suddenly there is not enough voltage to drive the ignition.

 

+1 . . . and as that connection resistance, in the face of major current draw, causes a rising voltage drop across connection, it generates HEAT . . . perhaps starting problem or compounding same until all cools down. Not unique to Jags, but I don't want to remember that learning episode quite some years ago. BTW, I do remember I verified with pack of frozen peas when wife Chris' back was turned!

I hope the fix is permanent Doug . . . and thanks Daim for correcting my bad on a CP sensor.

Cheers,

Ken

 

Haven't had a chance to drive the car much or update this thread of late. For various reasons I've been driving my work truck a lot these days.

Anyhow.....

The problem remains.

I spent a few more hours today digging. I might've find the problem but....heh heh...I've said that before. Cutting to the chase.....

I removed and opened up the amplifier and found one of the wires...the solid white one.... to the ignition module almost fell off when I touched it. The connector was just barely touching the post on the module. Sliding it onto the post revealed a sloppy fit. Not snug at all. I soldered a new connector onto the wire although a gentle squeeze with pliers would've probably restored the old one to a snug fit again.

I should know in a day or two if I hit paydirt. Hope springs eternal.

Cheers
DD

 

I bet that is it, Doug, and good for you for finding it. FWIW, if what has happened to me is any guide, it is an amp-related fault 9 times out of 10 when these funny symptoms appear.

 

Update:

A full week; no conking out. I'm cautiously optimistic

Cheers
DD

 

Well bloody done.

Another CHEAP repair to a very simple engine.