TPS sensor

The Oily Bits S1 Specific Topics
41

Trying using the Espirit V8 software on a laptop; then you can see the idle target, input speed to the ECU, when the ‘stationary idle’ is active, IACV demand and ignition advance. 1.1k is too low, the minimum idle speed should be 1250 rpm.

I changed my lambda sensor…it was a pig, and the threads from the sensor remained in the boss after I ‘persuaded’ it to come out. What was interesting is that the you can see the ECU switch in to closed loop mode, but the long term fuel trims don’t get adjusted. In fact, I couldn’t seen any difference in parameters when it swithces from open loop to closed loop, wonder if that aspect is disabled on the 190 ECUs?

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So I managed to get this out without too much drama yesterday

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New one has gone in and the car does drive smoother for sure, but my issue that is only ever induced at the same 6100rpm still prevails and then I’m back into the limp mode with the 5.5k limiter.

Could the fact that when it occurs it’s always at the same 6100rpm guide us to what the fault might be?

The VSS and TPS work based on the readings the obd…

Very peculiar! :thinking:

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I think the Rev limit only comes in if a missfire is detected. Do you have an error code for one?

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Found this from many years ago. May just be web noise. Con was very well respected in S1 Exige circles.

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Thanks I’ve come across that thread and Collin describes exactly what I am experiencing.

I have no engine light and no code, although maybe I should take the car to a garage with proper equipment as I’m just using a Bluetooth reader.

I’ve checked my speed sensor, it seemed fine, I also see a read out on the obd so the ecu is seeing speed. For £40 maybe I just change it as it’s intermittent.

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It may be worth checking your crank position sensor, sorry if you know this. The ecu detects misfire using the crank sensor which detects the timing teeth the flywheel. The ecu counts the teeth on each Rev until it should detect a missing tooth, which says the flywheel has done one Rev. If it counts an extra of missing tooth, it will cause an error which may put it in limp home mode. The ecu also looks at the timing of the teeth and expects to detect the acceleration of each cylinder firing. If it does not detect the speed up it claims a misfire.

It all depends on his the software is written on what it does!

Crank sensor fault, missing, extra tooth, missed accel, could cause limp home.

TPS fault, not detecting a closed throttle until late (if sticky).

Manifold air pressure fault. May cause a limit as the fuelling can’t be determined.

Temp sensor, I doubt that would set a Rev limit as even if faulty, the ecu would just assume 20C, but, who knows!

Baro pressure fault. Again, I’d expect the ecu to just assume 1 bar.

Vss, does strange things on the S1 Exige, I assume for compliance on emissions tests.

It could be any of the sensors as it depends on the software in the ecu.

Of course, check your plugs, plug leads and coil pack. It could be a genuine misfire which sets limp home but not a fault code. It’s not unusual for ecu code to ignore a few faults before setting an error code. Ecus also clear error codes if they have not seen the error for a while.

47

Can you provide some more details to narrow it down?

  1. Does rev limiting occur under slower acceleration (such as 50% throttle)?
  2. If ‘triggered’, can you get it above the the new limit with smaller throttle openings (for example, >20mph in 1st gear)?
  3. If ‘triggered’, does it reset after ignition off, or is is it due to cooling down?
  4. Have you tried new leads and a coil pack?
  5. Do you have a cat and if so, have you tried a bypass?
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@winthattt and @C8LGY Thanks for the help here guy’s. I drove into work today and conducting some more experimenting.

  1. Does rev limiting occur under slower acceleration (such as 50% throttle)? - Yes sampled in 2nd and 3rd gear today. Whatever level of throttle the 5.5k still comes in, and behaves just like a rev limiter.

  2. If ‘triggered’, can you get it above the the new limit with smaller throttle openings (for example, >20mph in 1st gear)? Nope.

  3. If ‘triggered’, does it reset after ignition off, or is is it due to cooling down? Turning the car off for 10 seconds or so removes the limiter.

  4. Have you tried new leads and a coil pack? No

  5. Do you have a cat and if so, have you tried a bypass? I have a decat fitted. I should say, this issue emerged a month or so after fitting the decat,

Crank sensor fault, missing, extra tooth, missed accel, could cause limp home. - I assume the only way to check if teeth are missing is to split the engine and box or remove the starter motor?

TPS fault, not detecting a closed throttle until late (if sticky). I’d be surprised if it was TPS as the “trigger” for this only ever happens on WOT. Also able to verify TPS on the OBD is working.

Manifold air pressure fault. May cause a limit as the fuelling can’t be determined. Lots of old rubber hoses and T pieces, does anyone sell a kit?

Temp sensor, I doubt that would set a Rev limit as even if faulty, the ecu would just assume 20C, but, who knows! Temp sensor working as confirmed by OBD

Baro pressure fault. Again, I’d expect the ecu to just assume 1 bar. I can see vacuum pressure on the OBD is this the same thing?

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You miss understand on the crank teeth. The timing wheel is made with a missing tooth to detect a revolution. I’d just check the crank sensor is clean, the connection is good and there is no damage to its tip where it is close to the wheel. It’s most likely fine as the car starts and runs ok.

I did not realise you have decat fitted, I don’t think the oxygen sensor you fitted would have any effect as it never gets a good reading with no cat.

Try new plugs. Worth doing anyway as VHPD engines eats them.

Make sure the ht leads look good, maybe change them and they are the correct ones for the coil pack. They must be the ones which push on tight to the coil connectors, not the ones which look like a bent copper ring. Elise parts sell them, you don’t have to get expensive magnecor ones.

Try a new coil pack, I think they are a Saab GM part, cheap on eBay. I have a spare but I cannot get to it after a major cycling crash.

Try refitting the cat. I think lots of people run them with no cat (which is illegal) but most cars will have a fit if the cat is missing.

Check if the TPS sticks by using your obd reader (engine stopped) and see if the obd reading follow you pressing the pedal. It will be a bit slow as obd id slow.

With obd check engine temp, baro pressure.

I think obd does not show manifold pressure. Yes the map and baro pressure uses that mass of little pipes. Sensors are cheap on eBay, as is the pipe.

I’d start with plugs Ht and refit the cat. It must stink without it!

Just checked and Elise parts have the plugs leads and coil packs. Yours must be 20 years old do with changing? EP will make sure you get all the correct stuff.

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Well if you’ve no cat fitted, that rules that out! I believe the Workshop manual mentions that they run slightly better without - I’ve certainly had no issues with removing the cat.

Based on what you’ve said above, if you can cycle the power and it clears the very specific rev limit of 5.5k - which we know is what it can do if losing speed input - it sounds like the ECU is not liking some input and calling time on the fun. The fact that it seems independent of throttle opening and engine load possibly makes fuel, intake and exhaust restrictions less likely.

I’ve no idea what would make the ECU do that other than speed input, but then again these ECUs are not that well understood. It could also be a crap signal that causes issues at higher frequencies, if it’s not a clean square wave like the ECU is expecting.

However, I’m not sure about that; if it was speed, then you’d expect that increasing road speed (frequency of signal) whilst keep the revs down to stay under the ‘trigger point’ would induce the behaviour? In other words, if you can get it to rev-limit in 2nd gear and that equates to 50mph, then doing 50mph in 5th without issues kinda makes that seem unlikely.

If it was the crank sensor, then I’d have thought the engine wouldn’t run, as it wouldn’t know when to inject fuel and spark.

Sorry that’s not much help - if it were me I’d be using an OBD program to log parameters, and then check them afterwards to see if a spurious signals stand out.

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Toby, might be worth a check of the HT leads connection to the coil pack. I previously had a 5500 rpm limit on mine that turned out to be the HT leads developing an air pocket at the coilpack end. The magnecor leads fitting instructions describe how to fit by carefully lifting the rubber boot on one side as the connection is engaged specifically to avoid air pockets. Worth a try?!

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Hey folks,

Family life has taken the front seat for the last few days but I managed to squirrel a few hours away today.

First up new plugs, leads and coil - no difference!

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However we have a new fault, the car isn’t enjoying any load below 2.25k but after then is fine.

I started replacing vacuum pipes and discovered this.

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I gather one of these devices is the MAP, what’s the other? I don’t believe either were connected…. Does anyone have a diagram of how it should be plumbed in?

EDIT - This thread claims to a Baro sensor, so I assume the inlet doesn’t connect to anything?

Lumpy running/running rich/vaccum pipes ? - The Oily Bits / S1 Specific Topics - Exiges.com

EDIT #2

So I see the factory routings includes the resonator valve actuator thats been removed on my car, and someone has kindly blue marked what they have here

Ok let’s talk vacuum hose’s… - The Oily Bits / S1 Specific Topics - Exiges.com

Does anyone have any conflicting views on how the routing below looks?

image

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We have recently sorted an S1 exige in the workshop.
John sorted those two sensors on it.
I will message him to respond here!!

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54

Thanks Dave - just edited my
Previous post in case you didn’t see with what would appear to be a sensible route.

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If you don’t have the resonance valve fitted, it’s a little easier. If you have/had AC it’s a bit more complicated - AC cars have 2 reservoirs, non AC just 1. Have a look above the brake master cylinder to see if there are more of the solenoid valves there, if there are, then your car has/used to have AC, or just the switch/vent layout in the cabin.
To run the engine happily, all you need is the top blue vac lines going across the throttle bodies, via the T pieces - one end goes to the fuel pressure reg and the other to the MAP sensor. Lose the T piece that goes to the vac reservoir to begin with. Make sure the rubber hoses are a good fit with no leaks, as 20+ year old rubber and plastic in an engine bay makes unhappy bedfellows. MAKE ABSOLUTLEY SURE that you connect to the MAP sensor, not the Baro sensor. The ECU can’t work out that they’re the wrong way round, and tries to run the engine in a very strange way! I’ve never seen a workshop fill with black smoke and soot quite so quickly when these are reversed.
Everything else vac pipe wise can be left alone as it’s not connected to the vacuum system at the moment. A better way going forward is to loop short lengths of hose between the valves, as it stops moisture getting into them.
Electrically wise, the charging and solenoid valves need to be connected. The MAP and Baro sensor need to be connected. The MAP and Baro sensors look the same, but aren’t and can be plugged in the wrong way around if you try hard enough. Annoyingly, you can fit the bracket the wrong way around and the connectors still reach.
I’ll get some pictures of a car in the workshop tomorrow and try to post them here, but the bracket with the 2 sensors on should be attached to the roll cage back stay with a couple of jubilee clips. Very high tech! You can just about see one mounting jubilee clip and either Baro/MAP electrical sensor connector in your picture, just by the fuel pipe going into the fuel filter.
Can you take a picture of each sensor? Showing the part number and the connector plug receiver? There are number of different types of those sensors, all with a different mBar range, and there should be a locking tab inside the connector, to try to stop you from plugging them in the wrong way around.

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56

Great reply! Interested to know why you think the solenoids should be connected electrically though, as they are supposed to be discarded if upgrading to 190 spec. Ingress protection?

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Thanks Folks, so lots of good progression…

The load below 2.5k is resolved, I’m fairly sure I knocked the vacuum line out of MAP sensor, the car is driving absolutely great now, pick up is ace!

I’m now back to the same issue in that I’m going into limp mode, so a summary of whats been looked at already.

  • Wheels speed sensor and wiring looks fine, I ran a data log of my OBD dongle today and at no point does the ECU see a random spike or drop etc
  • Plugs, leads, coil all brand new
  • Engine temp read out fine
  • vac lines all changes
  • MAP works as its now plugged in!
  • O2 sensor has been replaced.
  • TPS confirmed as working via the OBD dongle.

What would be the logic of refitting the cat?

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Ingress protection, yes as one. The last time I looked was a lot of years ago, the 340R ‘actually make 340bhp/ton’ kit stated to remove them as they were a bit desperate to hit the number. I can’t remember which way the Exige kit went. P1501 is ‘Resonator valve is not closing’
Can you look at the engine speed when the fault first occurs at 6100?
Have you had a look at the back of the flywheel? If you take the starter motor bolts out - disconnect battery first - then there’s a black plate under the nuts that can be removed to check the flywheel. As I’ve said before, there are some flywheels out there that are a bit light on the trigger. Also have a look at the crank sensor, as have seen a couple that are bent, which does odd things!

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Thanks JDS I’ll see if I can get a log of speed next time it happens.

Flywheel has not been inspected yet, but I just took the CPS out, looks okay, but filthy so cleaned up and back in…hopefully get a chance for a drive on Monday, we will see.

Strangely it has 3yrs on it, shelf life? lol

Before

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After

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3years?

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:nerd_face:it’s VRS, variable reluctance sensor. That’s what it is.

Just looked grubby to me but dirt does not stop the magnetic field. If it was damaged or covered in magnetic bits I would be concerned. Try it though.

JDS is giving good advice. As he says, my car has resonator error codes (they have been removed), but I do not get the Rev limit.

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