Struggling to start hot after rebuild

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thejaydogg
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Struggling to start hot after rebuild

Post by thejaydogg »

So I've recently had my engine rebuilt at RR. Had the housings refurbished and ported, RRP MK2 coils fitted and a full service completed as well. I have covered the 750 miles for the run-in and had no starting problems whatsoever at that point. At 750 miles I had an oil and filter change done by my local mechanic (oil and filter supplied by myself) and have been upping the revs slightly since.

Last Tuesday I was driving home from work and stopped off at Tesco to fill up the tank with Momentum 99 before heading inside to pick a few things up. About half an hour later I came back and went to start the car. The starter motor was spinning but the engine wasn't firing. After a few seconds I stopped and gave it another 10 seconds before trying to start again - this time it started as normal.

Since then it has happened twice more, under the same circumstances (hot engine sat for between 30 minutes-1 hour) however on both of these occasions the engine cranked to about 400-500rpm and required me to press on the accelerator a couple of times to get enough revs to sit at 1000rpm unaided. I've had a look at the OBD readings and it's throwing me no codes.

Any ideas?
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Re: Struggling to start hot after rebuild

Post by boosted »

Maybe help a 20 brake stomp?


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Re: Struggling to start hot after rebuild

Post by warpc0il »

It's not normally this extreme but it's not uncommon for many cars (not just 8s) with complex Powertrain Management Systems, to get confused under these sort of conditions.

Basically the air trapped within the intake is still quite hot from the heatsoak within the engine bay.
The PCM detects this and chooses a fuelling map appropriate to hot Intake Air Temperature.
However, as soon as the engine starts to spin on the starter that air is eaten by the engine and much cooler air is taken in from the outside, so now the map is wrong.

The result is usually a reluctance to start followed by quite rough running, sometimes even stalling, until the PCM works out what's happening.

The symptoms you describe sort of fit this model, especially as it started fine the second attempt, by which time all the trapped hot air would have been cleared.

The "hot start issues" related to low compression would be after only a 5 minute stop, rather than the 30-60 minute.
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thejaydogg (Sat Jul 20, 2019 5:25 pm)
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Re: Struggling to start hot after rebuild

Post by thejaydogg »

warpc0il wrote:
Sat Jul 20, 2019 3:36 pm
The symptoms you describe sort of fit this model, especially as it started fine the second attempt, by which time all the trapped hot air would have been cleared.

The "hot start issues" related to low compression would be after only a 5 minute stop, rather than the 30-60 minute.
That's reassuring to read. Would you say it's worth resetting the ECU for the fuel trims as boosted suggested above?
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Re: Struggling to start hot after rebuild

Post by ChrisHolmes »

You need to report this situation to Rotary Revs and seek their advice also. The above advice is all very relevant and correct but as RR warrant the engine they should always be your first port of call if you have any concerns.
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13Black (Sat Jul 20, 2019 5:18 pm) • thejaydogg (Sat Jul 20, 2019 5:24 pm) • Dr. FrankenRex (Mon Jul 22, 2019 8:52 am)
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Re: Struggling to start hot after rebuild

Post by warpc0il »

If I'm correct then resetting won't make any difference.

You should be checking with RR anyway
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Re: Struggling to start hot after rebuild

Post by SeeJay »

You have an R3 - the '20 pedal stomp' method for resetting the ECU doesn't work. You have to disconnect the battery for at least one minute.
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Re: Struggling to start hot after rebuild

Post by thejaydogg »

SeeJay wrote:
Sat Jul 20, 2019 6:24 pm
You have an R3 - the '20 pedal stomp' method for resetting the ECU doesn't work. You have to disconnect the battery for at least one minute.
I know that :thumright: I’ll ring RR on Monday to see what they think before trying anything off my own back.

Just took it on a drive to get the temps up. Will have a go at starting in 30-45 mins and video the results.
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Re: Struggling to start hot after rebuild

Post by boosted »

Learn something new everyday. Didnt know 20 brake stomp didnt work on r3.. think i did 1 on the wifes old r3 mind lol.

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Re: Struggling to start hot after rebuild

Post by Nickp47 »

Is that definitely true re R3? When I first got mine I cleaned the MAF as it was running poorly but it did not start running properly smoothly again until I did a 20 stomp (or thought I did one!)
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Re: Struggling to start hot after rebuild

Post by ChrisHolmes »

Maybe it does work but the later firmware, or whatever, does not cause the oil gauge needle to rise and fall
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Re: Struggling to start hot after rebuild

Post by thejaydogg »

Update: started on the button after around 40 minutes of sitting on the drive. I'd like it to not happen again obviously but I'll guess I'll keep videoing my start-ups (just in case) as a video would be a lot easier to show the symptoms than trying to type it out or describe it over the phone.
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Re: Struggling to start hot after rebuild

Post by SeeJay »

Nickp47 wrote:
Sat Jul 20, 2019 6:59 pm
Is that definitely true re R3?
Yes it is ;)

boosted wrote:
Sat Jul 20, 2019 6:48 pm
think i did 1 on the wifes old r3 mind lol.
..maybe,but you didn't 'reset' anything ;)
ChrisHolmes wrote:
Sat Jul 20, 2019 7:15 pm
Maybe it does work but the later firmware, or whatever, does not cause the oil gauge needle to rise and fall
It doesn't work,and the R3 has no oil pressure gauge..which wasn't really a gauge on the S1,anyway
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Re: Struggling to start hot after rebuild

Post by warpc0il »

Even S1s, either built with the later PCM firmware or updated by the dealers, don't sweep the oil gauge needle. That doesn't mean that they don't reset with the 20 stomp process - as they all do.

However, the full reset is a combination of the battery disconnection and the 20-stomp (1 stomp on R3's)
See https://www.rx8ownersclub.co.uk/forum/v ... 25&t=34703
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Re: Struggling to start hot after rebuild

Post by 350matt »

could be the crank / eccentric shaft sensor is on the way out
measure its resistance as it should be between 980 to 1250 ohm
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Re: Struggling to start hot after rebuild

Post by Dr. FrankenRex »

I'm fairly certain it does reset the limited bits that the 20 stomp does on the R3, it just can't show you it has because of the lack of oil gauge. Ultimately the 20 stomp does jaff all to 99.999% of cars, so I don't see why people keep perpetuating it as a save all ECU reset.

If you want to reset the fuel trims (as said, not sure this would help in this scenario either way) then you need to disconnect the battery. It doesn't even need to be for very long, just a short 10-20 seconds should do the trick.

Either way, as people above have said you should be chatting to RR as they built the engine (quite recently at that) so they will be able to assist.
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Re: Struggling to start hot after rebuild

Post by Juey »

Just a thought that it may be running a richer fuel map during run in......

Do RR make it run a different fuel map whilst running in a new rebuild? ...and then take it back to normal at the 1000 mile service point??

^^this is a guess, I've no idea if they would or not^^
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Re: Struggling to start hot after rebuild

Post by ChrisHolmes »

Juey wrote:
Mon Jul 22, 2019 11:06 am
Just a thought that it may be running a richer fuel map during run in......

Do RR make it run a different fuel map whilst running in a new rebuild? ...and then take it back to normal at the 1000 mile service point??

^^this is a guess, I've no idea if they would or not^^
I have never heard if anyone running a richer mixture during running in either a piston or rotary engine. Using a running in oil with fewer friction reducing additives yes but that applies mainly to older engines where running in was vital to have the piton rings and cylinder bores "bed in" but modern cylinder wall finishes have effectively removed the need for long running in periods.
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Re: Struggling to start hot after rebuild

Post by Alan.h »

if this has only happened since oil change. i would be checking the spark plug leads are on properly, when i change the oil on mine oil always runs down the block where the plugs are, so i obviously wipe it off with a rag, who is to say she garage that changed your have not done the same and dislodged a plug lead while cleaning any spillage off
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Re: Struggling to start hot after rebuild

Post by AndyBrad »

20 brake stomp works on my r3.

oil filter is under the car so not much chance of it running down.

id contact them and get a compression test.