Is it normal for a new engine to stall when it is first started?

[prisoner7]

I’m building 420SV (Ford, Mazda, LSD). I've run the engine for about an hour. When I start the engine, it immediately stalls. I have to rev the motor to about 1,110 RPM for about 5 to 10 minutes. After this time, the engine will idle smoothy at about 800 to 900 RPM. 

Is this normal?

And if it is normal, how many more hour(s) of run time does the engine need to run before this situation goes away?

Your thoughts are appreciated. Thanks.

[Jonathan Kay]

It turns, fires normally, and then stops?

And it has always done this?

Does it being cold or hot make any difference?

What's the battery voltage at rest, minimum while cranking, and at 3,000 rpm?

Is the fuel new?

Jonathan

[ScottR400D]

I think you’ll find the answer is yes.  Shouldn’t be like that but they very often are. 

[prisoner7]

Jonathan - brand new car. Fuel = 1/3 and fresh within the month. Battery is strong, not a voltage problem. This is from a cold start. Outside temperature around 10 degrees celsius .

Scott - does this problem go away?

[ScottR400D]

Not until the car’s set up properly often. Been like that for years.  My ‘15 car was like that till I had RBTBs fitted and mapping done. 

[simon_h]

There’s no idle circuit on the standard set up as there would be on a normal car so it might need a bit of throttle to keep it going until it’s warm enough to run on the air available at the set idle stop position. 

[Ainsley]

Mine didn't stall, but it varied its idle speed quite a bit.  I ran it up to temp to check for leaks and that the fan came on.  Adjusted the idle so it didn't stall.

Then on a shake down run its idle wavered about a bit, like it was hunting for the correct setting.  Then it went to Caterham for its PCB and they said its normal behaviour.  Once I've had it back and put some more proper miles on it I will see if it settles down. 

If not I will send it off for throttle bodies and remap earlier than planned, which will sort that out.

[ScottR400D]

If it gets set up properly by someone who knows what they’re doing and cares it will be fine. Just hoping it will get better doesn’t work. 

I'm not sure I’ve ever read so many posts going over things we’ve discussed so many times over so many years. 

You clearly haven’t spotted the elephant in the room yet…….

[prisoner7]

53 minutes ago, ScottR400D said:

If it gets set up properly by someone who knows what they’re doing and cares it will be fine. Just hoping it will get better doesn’t work. 

I'm not sure I’ve ever read so many posts going over things we’ve discussed so many times over so many years. 

You clearly haven’t spotted the elephant in the room yet…….

Scott - I did search for information about this before I posted this question. Unfortunately for me, I'm in the US and won't have access to CC's PBC. Thank you - all of you, for your inputs.

[ScottR400D]

9 minutes ago, prisoner7 said:

Scott - I did search for information about this before I posted this question. Unfortunately for me, I'm in the US and won't have access to CC's PBC. Thank you - all of you, for your inputs.

I wasn’t replying to you actually. I think all you need to know is that they’re not always well set up from the factory, CC will just make excuses but they can be fixed. I’m afraid in the USA you’ll have even less support than we get. The PBC wouldn’t help as shown above. 

[Ainsley]

What does an idle circuit do then ?

Is this something that adjusts the mixture to adapt to altitude / cold air / cold engine etc and tweaks accordingly.  So if the Caterham does not have one I can understand why you need to tweak it with your foot till its all at operating temp.

Or is the issue caused by it being mapped to pass emissions ?

[aerobod - near CYYC]

With the manufacturing tolerances in each engine, the idle will never be very good without careful adjustment for each engine without an idle control system. This means that the engine would need to be run at the factory in the car with the same fuel pump and air intake. Obviously with a self-build model this is not possible. An adjustment in the throttle blade position of 0.05mm makes a significant difference to the idle. The engine map at idle really needs to be specifically set up for the car, which isn’t going to be possible with a standard engine map in a locked ECU on an engine that isn’t running in it’s final fitted configuration.

When fully warmed up some basic idle control is provided by closed loop Lambda control, but with the narrow band sensor used, hunting should be expected if the mixture in the map is not close to the needed amount. Throttle stop adjustment may work on some engines, but the tolerances overall may be too much to get it close enough without an ECU remap.

[Ainsley]

Ah, that makes sense.

 

[MattB]

Caterham tweaked the idle on my 420 as part of the first service (the one where they get you to pay for them to check if they built the car properly …).

MattB

[AlastairA]

Had a similar issue with my build, in that on a cold start the engine would hunt around 900rpm. I used an MBE985 cable and the Easimap software to set the TPS a little more accurately. This resulted in a slightly higher idle speed but stopped the hunting. I later had a chat with the technician who performed the PBC and he confirmed that (a) this is a frequent issue (b) that adjusting the TPS was the usual fix and (c) it was now set correctly.

Edited April 29 by AlastairA

[StevehS3]

I recently setup my Sigma which was a case of using Easymap to accurately setup the TPS and throttle stop. Slight adjustments allowed it to idle cold and hot without hunting or needing to touch the throttle when cold to avoid stalling. When hot I aimed for zero Idle Air Prop Term Degrees to maintain the target RPM. 
I thought I read that the Duratec TPS wasn’t adjustable ie doesn’t have a slotted fixing to allow rotation. Based on my findings, there  isn’t much scope for getting it just right without being able to tweak the TPS position. 

[AlastairA]

3 minutes ago, StevehS3 said:

I thought I read that the Duratec TPS wasn’t adjustable ie doesn’t have a slotted fixing to allow rotation.

That's correct, but there is some slop in the mounting and you can bias it in one direction or the other. The rest of the setup has to come from the idle speed grub screw.

[ducatidentist]

Mine has just hit 1000 miles and yes it will still stall from cold soon after starting unless I feather the throttle, is fine once warmed up.

Will probably get it remapped professionally by Northampton Motorsport as they are close once out of warranty 

[aerobod - near CYYC]

Half a degree rotation of the TPS correlates to about 0.02V, about the amount of adjustment needed to even out the idle somewhat. That is only about 0.2mm of slack in the clamping hole. In adjusting the throttle stop screw, 30 degrees or so of rotation is the likely amount of adjustment that would be needed to change the air flow by an appropriate amount.

[prisoner7]

3 hours ago, AlastairA said:

Had a similar issue with my build, in that on a cold start the engine would hunt around 900rpm. I used an MBE985 cable and the Easimap software to set the TPS a little more accurately. This resulted in a slightly higher idle speed but stopped the hunting. I later had a chat with the technician who performed the PBC and he confirmed that (a) this is a frequent issue (b) that adjusting the TPS was the usual fix and (c) it was now set correctly.

I obviously need more tools. 

More to do, more to learn, this makes sense.

[Beagler]

Mine used to stall and sometimes took a few goes to get started and idled about 13-1400 rpm. Since having throttle bodies, lightened flywheel fitted and rolling road it now starts first press and idles straight away at 1000rpm. A little expensive but engine is transformed and goes like stink.

[Golf Juliet Tango]

On 29/04/2024 at 07:26, simon_h said:

There’s no idle circuit on the standard set up as there would be on a normal car so it might need a bit of throttle to keep it going until it’s warm enough to run on the air available at the set idle stop position. 

Agreed. And with a Crossflow it needs a minute to really settle down.