V8 hot start problem - the definitive thread

[swindon_alan 1,693]

My V8 has developed the infamous hot start problem. Starts fine cold but if the coolant temperature is over 70 degrees then it just won't restart. The CEL stays on but there are no ECM error codes. Weird. The solution is to wait twenty minutes or so for it to cool down. Very frustrating.

I have trawled the forum for solutions and found these two:

I met a chap called Tony at a Club Lotus Wessex shindig last year and we were discussing V8 problems. I mentioned my hot start problem and he smiled. "Yes", he said. "It's the camshaft sensor. I changed mine and it fixed it". Ah ok. The V8's crankshaft sensor is also used on a Ferrari F50 Coupe 4.7 (1995 to 1997). Uh oh. That's going to be expensive then...

For cross reference purposes here we go:

Lotus part number: A918E6010F

BOSCH
0 232 103 006

OE NUMBERS
BOSCH 31 65143 10105 6
BOSCH PG-3-1
FERRARI 150866
GMC 93216451
MAN 51 27120 0013
MTE-THOMSON 7303
ZMZ 25 3847
ZMZ DF-1

LUCAS ELECTRICAL SEB1236 Sensor, camshaft position

Ferrari 456 GT/GTA (1993 - 2004) 5.5 01.1993 - 06.2004 5.5 L 442 h.p. 325 kW F 116 B 00
Ferrari F355 GTS 3.5 07.1994 - 12.2000 3.5 L 380 h.p. 280 kW F 129B/40
Ferrari F50 Coupe (W16_)     1995-1997

STANDARD 17055
FUEL PARTS CS1294
STANDARD CS1294     Sensor, camshaft position
STANDARD EPS534     Sensor, camshaft position
INTERMOTOR - CAMSHAFT POSITION SENSOR - 17055

So anyway, you don't have to pay £180 for these, you can get them from a guy in Latvia for £125:

http://www.ebay.co.uk/itm/BOSCH-Camshaft-Sensor-Fits-FERRARI-456-F355-F50-GAZ-Volga-MAN-Lion-Nl-1972-/141793002797?hash=item210385852d:g:DloAAOSwdvpWEjGa

...which is what I did.

That was an easy swap, at the rear right at the top of the block. Did it work? Nope. Oh well. Interestingly the camshaft sensor is only used at start up to set the ECM crank position, you can disconnect it after the engine has fired up.

What next? Well looking at those threads the crank sensor could be duff. Temperature affected too, there is a possibility that it outputs garbage at low revs. Better try that then. Fortunately these are relatively peanuts, about £20 a pop.

Cross references:

Lotus part number: A910E6939F R /B : A918E6080F

The earlier 910 engine version is obsolete but the V8 one has direct replacements.

A910E6939F    Lotus factory part only. Not released to aftermarket    Sensor, Vehicle Speed (VSS) (MY 88 Delco fuel injection)          

As in used on the Lotus Elise and Exige Series 1s as a L/H rear hub speed sensor:

A918E6080F

SJ sell them for twenty quid. However, if you want to go elsewhere then they are:

GM 10456555
WELLS     SU137
CARQUEST     71-4829
ACDelco     213-148
AIRTEX     5S1665
DELPHI     SS10089
ADVAN-TECH     2H8

Or:

GM 10457661
CARQUEST     71-4860
WELLS     SU1115
MasterPro     2-96055
ORIGINAL ENGINE MANAGEMENT     96055
STANDARD MOTOR     PC7
STANDARD MOTOR PRODUCTS     PC7

Alex V8 kindly fitted my replacement on his lift today Did it fix the problem? NO. ARRRRGGGGGGGGGGGGGGGHHHHHHHH

Getting fed up this afternoon, I revisited the threads. Oh, so one fix was to change both sensors and put a battery negative post to engine block strap on. Ok then, let's whack a jump lead between the battery and the block. And...hot starts are now fine

Which is kinda counter intuitive really. I would have thought that if there was a voltage drop problem (which is what it felt like, low cranking speed, flickering CEL etc.) then a cold start should make more demands on the electrics. Weird. If someone has a rational explanation for this then please feel free to let us all know. Anyway, nice new earth strap ordered.

In the interests of helping anybody else who has the same problem, I now have spare working camshaft and crank sensors. If after trying the jump lead trick you still have hot start pain then I can send you my sensors to swap out and try and isolate the cause. If it is one of those then either send them back or source a replacement. They're sat in a Jiffy bag all ready to go

Phew. So happy!

[Vulcan Grey 251]

Glad it's working now for you.

 

FYI, this could also be leaking secondary injectors on the V8.  

[swindon_alan 1,693]

4 hours ago, Vulcan Grey said:

Glad it's working now for you.

FYI, this could also be leaking secondary injectors on the V8.  

Thanks Travis. Yes, I saw a reference to the injectors in one of those threads and noticed that it did fix someone's problem. Excellent, so we have a defined fault finding path then?

1. Earth lead (easy fix)
2. Camshaft sensor (not cheap but easy to do)
3. Crankshaft sensor (cheap but more difficult to get to)
4. Secondary fuel injectors (2 x $50-ish and some work)

Any other known fixes to add?

[superdavelotus 124]

That's great news Alan, just a shame you don't live closer to me to have a look at mine. I've tried everything apart from rewiring the O2 sensors, change the fuel pump (although I need someone to test the pressure) or take the plenum off!

So was your problem with earth lead due to it being loose or breaking down?

[swindon_alan 1,693]

36 minutes ago, superdavelotus said:

That's great news Alan, just a shame you don't live closer to me to have a look at mine. I've tried everything apart from rewiring the O2 sensors, change the fuel pump (although I need someone to test the pressure) or take the plenum off!

So was your problem with earth lead due to it being loose or breaking down?

It's a strange one Dave. I haven't checked out the earth leads to see if there is corrosion or whatever. According to the wiring diagram:

The battery negative post is tied first to a chassis ground and then to an engine ground.Assuming this is all chunky braided cables then why on earth it should be temperature affected I have no idea. Unless something is going on with the resistance of corroded metals with heat? I don't understand...

Anyway, if having a direct strap between the battery and block fixes the problem then it can't do any harm. Interestingly it has a much more stable idle now as well.

[superdavelotus 124]

Hi Alan,

So where did you connect the jump lead to exactly? I know I have completely different problem to yours but I am going to rule this out on mine as it's a free and simple job. My problem is O2 voltages dropping and engine stuttering. Not sure if this is a wiring problem or fuelling problem (air leak) and ECU and O2 sensors are actually doing their jobs? 

[swindon_alan 1,693]

13 minutes ago, superdavelotus said:

Hi Alan,

So where did you connect the jump lead to exactly? I know I have completely different problem to yours but I am going to rule this out on mine as it's a free and simple job. My problem is O2 voltages dropping and engine stuttering. Not sure if this is a wiring problem or fuelling problem (air leak) and ECU and O2 sensors are actually doing their jobs? 

One end on the battery negative terminal connector, the other to a shiny bolt head on the back of the block. Doesn't matter where you connect that one.

[swindon_alan 1,693]

1 hour ago, swindon_alan said:

The battery negative post is tied first to a chassis ground and then to an engine ground.Assuming this is all chunky braided cables then why on earth it should be temperature affected I have no idea. Unless something is going on with the resistance of corroded metals with heat? I don't understand...

I'm still rather puzzled and intrigued by this. I'm going to take the jump lead off and measure the battery negative post to block resistance with a multimeter, cold and hot when I have a minute.

I have had a quick dig around on Google but can't find anything on the resistive properties of corroded metals vs temperature. If it is corrosion then cleaning up the earth braid fixing on the block should sort it rather than running another wire in...

[LotuStuart 91]

strange problem....

My initial thought is that hot start problems are connected with fuel vaporisation, so need to do a thought experiment on why an extra earth strap would fix the problem.

Also, a real PITA problem. I stalled mine in heavy traffic last week, and it restarted just fine. But I would not like to have had to pop the engine cover and start connecting my jump leads in that situation....

So, how long a lead did you need to do this? I'd prefer preventative maintenance, and it can be done at the same time as my coolant flush and aircon rad....

 

On 14/03/2016 at 09:22, swindon_alan said:

I'm still rather puzzled and intrigued by this. I'm going to take the jump lead off and measure the battery negative post to block resistance with a multimeter, cold and hot when I have a minute.

I have had a quick dig around on Google but can't find anything on the resistive properties of corroded metals vs temperature. If it is corrosion then cleaning up the earth braid fixing on the block should sort it rather than running another wire in...

also check to see if there is a voltage difference between the block and the battery -ve.

[swindon_alan 1,693]

27 minutes ago, LotuStuart said:

also check to see if there is a voltage difference between the block and the battery -ve.

Good point, will do that too, hot and cold with the engine stopped and also running (ignition on).

I read a post last night on an instance of someone putting their gearbox back on and having the earth strap on the gearbox face rather than the engine side. Caused him all sorts of problems before he went back to his before and after photos. Food for thought...

[Barrykearley 6,856]

Sounds like it could be another problem with your gearbox @swindon_alan - best you swap it with mine 

[swindon_alan 1,693]

2 minutes ago, Barrykearley said:

Sounds like it could be another problem with your gearbox @swindon_alan - best you swap it with mine 

Ooooh, you think so Barry? Well if that's going to fix the problem then definitely! I will hoof it out tonight and drop it over to you

[Vulcan Grey 251]

On 3/14/2016 at 00:58, swindon_alan said:

Thanks Travis. Yes, I saw a reference to the injectors in one of those threads and noticed that it did fix someone's problem. Excellent, so we have a defined fault finding path then?

1. Earth lead (easy fix)
2. Camshaft sensor (not cheap but easy to do)
3. Crankshaft sensor (cheap but more difficult to get to)
4. Secondary fuel injectors (2 x $50-ish and some work)

Any other known fixes to add?

I think you should also add charcoal canister issues to the list.  If you can vent the fuel filler cap(s) and get the engine to start, then it is excess fuel vapor being purged into the manifold via the charcoal canister.

[swindon_alan 1,693]

Excellent, so we have a defined fault finding path then.

1. Earth lead (easy fix)
2. Charcoal canister - all US + ROW '01 on -  if you can vent the fuel filler cap(s) and get the engine to start, then it is excess fuel vapor being purged into the manifold via the charcoal canister (easy to diagnose)
3. Camshaft sensor (not cheap but easy to do)
4. Crankshaft sensor (cheap but more difficult to get to)
5. Secondary fuel injectors (2 x $50-ish and some work)

Any other known fixes to add?

[Vulcan Grey 251]

The o-rings on the secondary injectors are known to leak into the manifold, since they are galley fed injectors rather than the normal rail fed.  This often happens immediately after someone has disassembled the manifold and re-assembled it, since the o-rings get smashed or cut.

 

[swindon_alan 1,693]

Excellent, so we have a defined fault finding path then.

1. Earth lead (easy fix)
2. Charcoal canister - all US + ROW '01 on -  if you can vent the fuel filler cap(s) and get the engine to start, then it is excess fuel vapor being purged into the manifold via the charcoal canister (easy to diagnose)
3. Camshaft sensor (not cheap but easy to do)
4. Crankshaft sensor (cheap but more difficult to get to)
5. Secondary fuel injectors - the o-rings on the secondary injectors are known to leak into the manifold, since they are galley fed injectors rather than the normal rail fed.  This often happens immediately after someone has disassembled the manifold and re-assembled it, since the o-rings get smashed or cut (cheap but some work)
6. Secondary fuel injectors failed and leaking (2 x $50-ish and some work)

Any other known fixes to add?

[swindon_alan 1,693]

On 14/03/2016 at 09:22, swindon_alan said:

I'm still rather puzzled and intrigued by this. I'm going to take the jump lead off and measure the battery negative post to block resistance with a multimeter, cold and hot when I have a minute.

I have had a quick dig around on Google but can't find anything on the resistive properties of corroded metals vs temperature. If it is corrosion then cleaning up the earth braid fixing on the block should sort it rather than running another wire in...

Experiment done and completely no difference in battery negative terminal to block resistance, voltage, hot or cold, with or without jump lead. To prove the point I took the jump lead off with the engine hot and no, it wouldn't start. Put it back on and it fires up fine.

I really don't understand!!!!

[Vulcan Grey 251]

your meter won't be able to tell the difference with a good connection or bad connection, both look about the same until you crank some serious amps through the conductor.  THe braided straps that Lotus uses can suffer from corrosion between all the little strands, increasing contact resistance, which will change intermittently.   IF you cleaned up all the ground wires, strip the corrosion, and then use a dielectric grease on the wires and connections, it should work just as well as the jump lead.

[Barrykearley 6,856]

Don't bother trying to understand it Alan - the braided straps shagged - just replace it !!

[swindon_alan 1,693]

2 hours ago, Vulcan Grey said:

your meter won't be able to tell the difference with a good connection or bad connection, both look about the same until you crank some serious amps through the conductor.  THe braided straps that Lotus uses can suffer from corrosion between all the little strands, increasing contact resistance, which will change intermittently.   IF you cleaned up all the ground wires, strip the corrosion, and then use a dielectric grease on the wires and connections, it should work just as well as the jump lead.

I get this. Completely. If the earth braid is corroded then obviously it will affect maximum current flow. However, why there is a difference between starting cold and not starting hot is not explained.

My thinking is counter-intuitive. A cold engine should take more amps to crank, hence a bigger voltage drop on the battery and potentially too low for the ECM to work. A hot engine should take less amps to crank and a smaller voltage drop hence less effect on the ECM. It's the other way around!

@Barrykearley yeah, yeah, I hear you and I will replace the bloody things anyway. Unfortunately I am a physicist by education and I hate mysteries!

[LotuStuart 91]

Maybe it's something to do with the battery having less charge after it's been running?

thinking laterally....

[Barrykearley 6,856]

My money's on the strap being fubar'd

[LotuStuart 91]

But the question is, why the problem when hot?

[Barrykearley 6,856]

A wise man once said

"Don't look for problems - look for solutions"

im off to find more cider..

 

[silverfrost 1,387]

4 hours ago, Barrykearley said:

A wise man once said

"Don't look for problems - look for solutions"

im off to find more cider..

 

A wiser man once said   Dont give me problems, give me solutions.