Faint oil tell tale lamp/light at idle after starter motor change on GT3

[Red]

I've just changed out the starter motor on my 97 GT3, which involved raising the rear a little, removing the boot floor. Pig of a job because the inner bolt was not budging and it had a longer than standard starter in there.

Job is all done. Reconnect the battery. Car starts. Lovely.

But....the oil pressure light is on! But the gauge has pressure.

I checked the oil levels. Lowered the car down and let it settle in case days being raised had drained a sensor or oil. Tried again, and same problem.

The light only comes on below 1600 rpm and the gauge reads as having pressure, it's running Castrol EDGE SUPERCAR 10W-60, which I believe was what our gracious @Sparky filled it with when he got it back on the road, so I don't think it's oil related. It's also faint. When the key is in position 1 it's about twice as bright and in line with the other lights.

It hadn't done this at all before the starter change. I've checked all the fuses in the front and by the battery in case I blew one. I think I connected everything back up, but there is a connector just below the expansion tank that goes nowhere.

I've got an MOT on Monday, and I'm wondering if it's OK to drive.

Any ideas what this light, faintly, and only below 1600 rpm means?

Edited April 10 by Red
Added photo of mysterious connector

[Chillidoggy]

There’s something in the service notes about the oil pressure warning lamp. I have a feeling it only operates above a certain rpm, to stop owners getting windy about low pressure. Probably a relay in there. So, have a look at your service notes first.

Oh, and replace that hose clip that’s about to fail due rusting through. Easier to do it in the garage than at the side of the road at 2am in the pissing rain.

[Red]

Yeah, there is an engine speed relay to "prevent unnecessary concern", which seems to be working as it goes out if I rev it over 1600rpm. Why is it on under 1600rpm though? 

[Chillidoggy]

Connect a mechanical gauge up to determine the oil pressure across the range. If it’s within tolerances, then perhaps the low oil pressure switch is faulty.

[LotuStuart]

On 11/04/2024 at 10:17, Red said:

Yeah, there is an engine speed relay to "prevent unnecessary concern", which seems to be working as it goes out if I rev it over 1600rpm. Why is it on under 1600rpm though? 

If it was working, this would be the other way round-that the light would NOT come on below 2000rpm.

Sounds like that relay/control unit has a bad connection or is broken.

[Chillidoggy]

What colour are the wires that go to the mystery Delco connector?

[Red]

Mystery solved. I said the oil light was a feint glow, well under the right lighting circumstances I saw that the battery light was also kinda glowing. As it's just an outline light it was only really visible with cupped hands.

As it was now even more likely to be a charging issue, and seemingly a small one as it was starting fine and went out with a bit of revs, I decided to go for the MOT the next day. My working theory was that the alternator was fading and not charging enough for the circuit to be happy at idle.

I took it for a nice long run before the MOT to get the CATs warm and had no issues. Once warmed up the lights even went away at idle. 

The car breezed the MOT with only minor tom-foolery to get the emissions in line. And the MOT guy even turned the car around to save me doing it. And stalled it. And couldn't get it started. And the rear hatch latch didn't want to open! This was going downhill very fast. I managed to get the hatch open and jumped a start off a little jump pack, and nearly took off without paying. After paying the short drive home was anything but smooth. I had oil pressure but it was not happy unless it had some revs. I kept going towards home diagnosing, panicking and reducing the distance to walk home simultaneously.

In the road that leads to my road I was passing a line of parked cars, (sorry, lurching past a line of parked cars) when I spotted I now had no oil pressure, so an immediate stop was made once I had room to stop. Some more panicking, this time on the phone to a mechanically savvy friend, and I ended up walking home and using the daily to ferry the battery back and forth to top it up with electrons. After that it was fine to get home.

A couple of days later with the tools out and sat in the boot once more I found the issue. I hadn't connected a cable to the starter! I know what I did. I disconnected 2 groups of cables, and reconnected 2 cables, not seeing the other one wrapped in black and tucked under the starter. I'm amazed the Esprit does so well for running without an alternator. Maybe it uses the power wire for warning circuitry. I doubt someone else will be stupid enough to end up here searching for the same issue, but if you are, say hello.

[Chillidoggy]

If you leave the alternator excitation wire off, I can confirm with 100% certainty that an Esprit will run from Margate almost to Brand Hatch before it farts around and dies by the side of the motorway.

[Bibs]

Lotus Festival, 2016?

[Chillidoggy]

2 hours ago, Bibs said:

Lotus Festival, 2016?

Give the man a coconut!

Rescued by Sparky and Chris Internets, using a fag-packet sized battery booster.

[Kevin Wheeler]

The wire to the battery disconected from the alternator somewhere on the A303 from Yeovilton. I made it to Andover before I called the AA. In that time, the Tachometer stopped. The clock stopped. Apparently, I was doing 20 gallons to the mile at the rate my fuel guage was dropping. The Voltmeter was in the red (as you would expect). And I had no oil pressure. But, the engine ran for miles and miles. Eventually hiccupping enough for me to stop at a friendy Starbucks.

Watching the gauges, I thought that it was an electrical problem (rather than oil pressure). Which it proved to be looking at the alternator. If only I had had a crimping tool and a connector, I need not have called the AA. But how oftern do you need those in the car?