Introduction aaaand...limp mode

Topics relating to the Lotus Exige S1 (series 1)
hda
Posts: 31
Joined: Thu Sep 30, 2021 1:52 am

Hello everyone, I just recently got an Exige S1...well, recently, it was last summer but just in the past couple of weeks we (we as in the mechanic) have been starting to work on it. I live oversea and spend my summer vacations in Italy: what better car than an Exige S1 with no aircon to drive around Milan's traffic in 38C temperatures? :thumbup:

Since the maintenance was known but old, i proceeded to change radiator, brakes and pads, all fluids, plugs etc.

Today we took it for a drive and after a couple of 8000rpms shifts the engine dies down and now revs only to 5500rpms.

I am looking for this forum's help and to tap into your knowledge to see if you can help (aside from saying "get an Emerald" :D )
  • Speed sensor was replaced - no effect
    crankshaft sensor was replaced - no effect
    wires, relais and fuses behind the seats have been checked - nothing wrong
Next step will see if the wiring from the speed sensor to the ECU is faulty (does anyone have a wiring diagram?)

the diagnosis tool says "speed sensor error" but after trying with 3 different ones we all had the same result: 8000rpms for a couple of gears and then boooooooo limp mode.

Help!?
Do you think the ECU is faulty and if I try with another 170hp one I may solve it?

Cheers,
Andrew
S1 #261
JDS
Posts: 1342
Joined: Sun Aug 10, 2008 7:46 pm

5500 rpm rev limit was usually an ECU engine protection mode.
Most often cased by, in no particular order
Poor connection at coil pack - make sure plug leads are correct to coil connection - GM made 2 sorts, internal and external pole, and the two don't interchange, both coils and plug leads.
Vehicle speed sensor - are you getting a good reading at the ECU, not the dash, as there are 2 and independent of each other.
Crank sensor - have seen a couple of these now, where some aftermarket flywheels only have 1 set of trigger teeth to one side of the sensor. Seems to be no problem on Elise's, but Exige/340R with the EFi ECU, some don't like it. We have got around it by machining the mounting leg on the crank sensor slightly, so that it goes further into the hole in the block. Don't go too far though, as you will knock the tip of the sensor off or bend it on the flywheel!!
What is the fault code? Engine speed or vehicle speed fault?
hda
Posts: 31
Joined: Thu Sep 30, 2021 1:52 am

The coils are a bit old but they look good. Upgrading them is next as that would not hurt.

When you say “ Vehicle speed sensor - are you getting a good reading at the ECU, not the dash, as there are 2 and independent of each other.“

Does it mean that there are 2 sensors? Or that the signal splits to ECU and Dash? Speed at the dash is fine.
S1 #261
JDS
Posts: 1342
Joined: Sun Aug 10, 2008 7:46 pm

2 sensors for speed. Left rear for the dash and right rear for the ECU.
hda
Posts: 31
Joined: Thu Sep 30, 2021 1:52 am

JDS wrote: Thu Jun 16, 2022 6:06 am 2 sensors for speed. Left rear for the dash and right rear for the ECU.
We only tested the right rear to the ecu as the dash was fine
S1 #261
hda
Posts: 31
Joined: Thu Sep 30, 2021 1:52 am

The error code that we get is P0501 “ Speed Sensor vehicle A”
S1 #261
User avatar
deggles
Posts: 220
Joined: Tue Feb 26, 2008 12:22 pm
Location: Leeds

Hi & welcome :) I can't really help beyond what's already posted, but I had a very similar issue with mine, 5500rpm limit and various fault codes. Swapped sensors, checked wiring, nothing. I'm 99% convinced it was an ECU fault as I swapped in a borrowed unit from another car and that worked fine. I'm now running an Emerald!

There are wiring diagrams in the Exige supplement of the service manual (just Google for A111T0327J or PM me and I can send you a PDF) and there's some details on the bulkhead ECU connector pinout over here viewtopic.php?t=19169 if you want to do some continuity testing.

Seen a couple of similar threads recently, I do wonder if these old EFI ECUs are starting to show their age, maybe 20+ year-old electronics inches from a toasty exhaust manifold, it's to be expected!?
hda
Posts: 31
Joined: Thu Sep 30, 2021 1:52 am

The theory that the ECU may be starting to get old might make sense.

BTW this is totally expected- I guess it’s part of the journey .
S1 #261
Evoman
Posts: 156
Joined: Fri Apr 03, 2015 12:00 pm

I occasionally get a stutter at 5500rpm and the car won't rev past this point.

Every time I know what it is.

An air pocket can develop where the HT leads connect to the coil pack. The instructions with the HT leads even describes seating them carefully by lifting the rubber boot at one side as they are located into position to ensure no air pocket is trapped when they are fitted.

I disconnect each HT lead and reseat. Strange phenomenon but it happens. Why I don't know. Does this happen on any other car?!

Good luck ;)
hda
Posts: 31
Joined: Thu Sep 30, 2021 1:52 am

Thanks for the tip.
At this point I have the following options:

1- Leave with the mechanic as he takes it to an "ECU guy" to look into this and pray.
2- Drive as is (limp mode) while in Italy, then drop it off to get a megasquirt installed
3- Order an Emerald (which will take about 10 days all said and done) At this point I would get the pulleys too, maybe get the car ready by mid july (maaaaaaybe)
4- Order a megasquirt - no idea on timing.
S1 #261
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