car starts right up when cold, but has hard time starting when hot

[DLockwood]

Mine has done this for many years. Every time I start the car, even from cold now, I wait for the fuel pump to prime and light on dash to go out before cranking. Starts straight away every time, hot or cold.

Problem was I waited for the lights and priming finished before attempting to start, not just key in and crank…also tried the re prime again and the hot issue is still there. It’s almost like hot air temperature is affecting something electrical to hinder the starting process and after a bit of cranking I would say 4-6 seconds it finally started and ran fine, it’s really odd.

 

[DLockwood]

Problem was I waited for the lights and priming finished before attempting to start, not just key in and crank…also tried the re prime again and the hot issue is still there. It’s almost like hot air temperature is affecting something electrical to hinder the starting process and after a bit of cranking I would say 4-6 seconds it finally started and ran fine, it’s really odd.

Also not sure if it’s the hot cabin temperature or hot engine bay temperature that’s the main issue….old cars…. Here’s a couple pics

 

[Honcho]

Your FPR is 30 years old, so definitely check pressure. Like Old Guy said, it should hold line pressure after the priming function. The FPR just uses a rubber diaphragm to control flow, so it's possible the rubber has cracked or failed completely from just being old.

The hot start issue (not main relay related) is a known thing about the NSX and everyone experiences it. It's usually when the weather is very hot. No one has really been able to nail it down for the cause, but speculation is that the engine heat and hot IAT causes vapor issues in the combustion chamber that inhibits a clean start. The typical solution is to give it some gas when starting and it usually fires up, stumbles a little and then runs normally. NSX Life lol.

The OEM ECU is quite good and can handle most situations. We have a tuning solution for it and you should contact @MotorMouth93 if you want to know more. However, considering you are in AUS, the Haltech ECU is local to you with many excellent tuners. I'd go that route- it's far superior to the 80's tech in the OEM.

 

[Old Guy]

An OEM NSX does not have an electronic fuel pressure sensor. The fuel pressure regulator does have a vacuum line to the intake manifold to provide a pressure bias based upon intake manifold pressure; but, a problem with that should not create a hot start issue. Since you installed a new FPR (along with just about everything else in the fuel supply system) I would expect that your fuel pressure should be correct; but, since you have no other obvious contributors to the hot start problem testing the resting fuel pressure will be the acid test.

The engine modifications you identify should not contribute to a hot start issue.

Have you pulled the spark plugs to have a look at the center insulators down around the base? If your insulators are dark tan - brown then maybe you are having an over fuelling issue which is compromising hot starts. If the fuel pressure checks out OK and the injectors are the original spec (have you actually checked to confirm that a previous owner did not switch out the injectors?) and are not leaking then maybe Spoon fiddled with the ECU beyond just modifying the ignition maps. As Honcho suggested, perhaps try contacting them to see if they will fess up on what has been modified in the ECU (if they still have anybody alive who remembers what they did 30+ years ago). However, right now I would focus on making sure the problem is not somewhere else before diving down the ECU rabbit hole.

Now a little rant about aftermarket ECUs being better.

Since your engine is a C30 the only modification that might benefit from some alteration of the fuel map is the switch from the original cast iron headers to a tubular exhaust manifold. However, NSX owners with C30s on this side of the Pacific have been replacing their cast iron headers with tubular headers and continuing to run the OEM ECU with unmodified fuel maps without reporting any issues.

From an OEM perspective, more modern processor technology is more about managing more elaborate turbo charging systems, combined direct and port injected fuel systems and managing the increasingly complex emmission control systems. The aftermarket guys are doing this because they need something new to sell you to stay alive. A huge driver for increased chip I/O and clock speed at the OEM level has been the explosion in self diagnostics after the implementation of OBDII. I expect that OBDII and its more complicated post OBDII versions is a bigger processor burden than the rather simple fuel calculations on a MAP engine. You have a naturally aspirated port injection engine with the only complication being the requirement for EGR maps for NOX control and the maps for VTEC control. Faster processors with more memory and I/O capability will yield no performance up side as long as you are sticking with a basic naturally aspirated port injected engine with mostly passive emission controls.

Technically, the Na1 OEM ECU of your generation does not come with tuning flexibility. However, now that the external ECU memory has been mapped, with a little hardware modification and the associated tuning interface you have the ability to modify the fuel, ignition, Vtec and EGR maps which gives you more tuning flexibility that you need. However, if you don't have the skills to modify the ECU and do the set up yourself then you are kind of stuck with using an aftermarket ECU and tuner to do the work for you. Just know that they will never do as good a job as Honda at configuring the ECU. Also, be aware that aftermarket ECUs have a limited support life. When AEM and other vendors release a new ECU they usually drop support for the older ECUs a year or two later. At that point if your local guy also ceases to support the ECU you are on your own. I think that there are a few AEM (or whoever) owners that concluded that the solution to surviveability was to have a back up ECU with the tune copied over to that ECU so they did not have to repeat the whole configuration process with a new ECU.

 

[DLockwood]

Your FPR is 30 years old, so definitely check pressure. Like Old Guy said, it should hold line pressure after the priming function. The FPR just uses a rubber diaphragm to control flow, so it's possible the rubber has cracked or failed completely from just being old.

The hot start issue (not main relay related) is a known thing about the NSX and everyone experiences it. It's usually when the weather is very hot. No one has really been able to nail it down for the cause, but speculation is that the engine heat and hot IAT causes vapor issues in the combustion chamber that inhibits a clean start. The typical solution is to give it some gas when starting and it usually fires up, stumbles a little and then runs normally. NSX Life lol.

The OEM ECU is quite good and can handle most situations. We have a tuning solution for it and you should contact @MotorMouth93 if you want to know more. However, considering you are in AUS, the Haltech ECU is local to you with many excellent tuners. I'd go that route- it's far superior to the 80's tech in the OEM.

Hey thanks for the reply, the fpr is a brand new oem unit I’ve just put in, I will try different starting methods next time and see how it goes. Thanks for the ecu Info I’ll definitely look into them.

 

[DLockwood]

An OEM NSX does not have an electronic fuel pressure sensor. The fuel pressure regulator does have a vacuum line to the intake manifold to provide a pressure bias based upon intake manifold pressure; but, a problem with that should not create a hot start issue. Since you installed a new FPR (along with just about everything else in the fuel supply system) I would expect that your fuel pressure should be correct; but, since you have no other obvious contributors to the hot start problem testing the resting fuel pressure will be the acid test.

The engine modifications you identify should not contribute to a hot start issue.

Have you pulled the spark plugs to have a look at the center insulators down around the base? If your insulators are dark tan - brown then maybe you are having an over fuelling issue which is compromising hot starts. If the fuel pressure checks out OK and the injectors are the original spec (have you actually checked to confirm that a previous owner did not switch out the injectors?) and are not leaking then maybe Spoon fiddled with the ECU beyond just modifying the ignition maps. As Honcho suggested, perhaps try contacting them to see if they will fess up on what has been modified in the ECU (if they still have anybody alive who remembers what they did 30+ years ago). However, right now I would focus on making sure the problem is not somewhere else before diving down the ECU rabbit hole.

Now a little rant about aftermarket ECUs being better.

Since your engine is a C30 the only modification that might benefit from some alteration of the fuel map is the switch from the original cast iron headers to a tubular exhaust manifold. However, NSX owners with C30s on this side of the Pacific have been replacing their cast iron headers with tubular headers and continuing to run the OEM ECU with unmodified fuel maps without reporting any issues.

From an OEM perspective, more modern processor technology is more about managing more elaborate turbo charging systems, combined direct and port injected fuel systems and managing the increasingly complex emmission control systems. The aftermarket guys are doing this because they need something new to sell you to stay alive. A huge driver for increased chip I/O and clock speed at the OEM level has been the explosion in self diagnostics after the implementation of OBDII. I expect that OBDII and its more complicated post OBDII versions is a bigger processor burden than the rather simple fuel calculations on a MAP engine. You have a naturally aspirated port injection engine with the only complication being the requirement for EGR maps for NOX control and the maps for VTEC control. Faster processors with more memory and I/O capability will yield no performance up side as long as you are sticking with a basic naturally aspirated port injected engine with mostly passive emission controls.

Technically, the Na1 OEM ECU of your generation does not come with tuning flexibility. However, now that the external ECU memory has been mapped, with a little hardware modification and the associated tuning interface you have the ability to modify the fuel, ignition, Vtec and EGR maps which gives you more tuning flexibility that you need. However, if you don't have the skills to modify the ECU and do the set up yourself then you are kind of stuck with using an aftermarket ECU and tuner to do the work for you. Just know that they will never do as good a job as Honda at configuring the ECU. Also, be aware that aftermarket ECUs have a limited support life. When AEM and other vendors release a new ECU they usually drop support for the older ECUs a year or two later. At that point if your local guy also ceases to support the ECU you are on your own. I think that there are a few AEM (or whoever) owners that concluded that the solution to surviveability was to have a back up ECU with the tune copied over to that ECU so they did not have to repeat the whole configuration process with a new ECU.

Thank you for the detailed explanation. The injectors are original to the best of my knowledge, the spark plugs seemed normal when I removed them last and replaced with new ones but I will go back and double check them. If overfueling was an issue I would have thought there would also be other symptoms?

Ecu wise I will keep this spoon ecu and see what I can do with it and also maybe even find a oem one too, in terms of aftermarket here I was looking at an emtron ecu in future as I look into programming it for Toda ITBs / cams.

Before I do any of that I just want to make sure everything else with the engine is working as it should and nothing maintenance wise needs my attention causing my hot start issue. I have accepted it’s a 30+ year old car it’s just every time I go drive it I forget haha.

 

[DLockwood]

Hello, Mike from South Africa, I own a Holden Ve s1 2010, it also recently started to misbehave when restarting, it's like it doesn't wanna start but eventually start in a strange engine sound like growling. This happens only after the engine was running. Cold start has no issues. Please help on what should I look at. And again it now showing stability control faulty and the rear wheel sensors where replaced but it still keeps the faulty stability error on the dash, then esp shows off. please help.

Regards

Sell it and buy a NSX

 

[DLockwood]

What is nsx?

It is the god of gods

 

[Old Guy]

A final kick at this. Since your car is a 1991 it will have an electronic idle air control valve (EACV). A lot of engines will improve their hot start by having 'a little more air' available during the start. On the early NSX the only way to do this is by having the ECU opening the EACV a little bit. I don't know whether the NSX does this; but, it is easy enough to check. During a hot start, press down on the throttle pedal slightly before engaging the starter to see if this improves start up. If it does then there might be an issue with the EACV preventing it from opening fully. Normally, EACV problems manifest themselves as idle speed control problems. It is also possible that the engine coolant temperature sensor (which is different than the gauge sensor) is out of spec and is providing an incorrect temperature value to the ECU which is screwing up start-up.

If pressing down on the throttle a bit does not help, then it is not a start up air issue and yo need to look elsewhere.

 

[DLockwood]

A final kick at this. Since your car is a 1991 it will have an electronic idle air control valve (EACV). A lot of engines will improve their hot start by having 'a little more air' available during the start. On the early NSX the only way to do this is by having the ECU opening the EACV a little bit. I don't know whether the NSX does this; but, it is easy enough to check. During a hot start, press down on the throttle pedal slightly before engaging the starter to see if this improves start up. If it does then there might be an issue with the EACV preventing it from opening fully. Normally, EACV problems manifest themselves as idle speed control problems. It is also possible that the engine coolant temperature sensor (which is different than the gauge sensor) is out of spec and is providing an incorrect temperature value to the ECU which is screwing up start-up.

If pressing down on the throttle a bit does not help, then it is not a start up air issue and yo need to look elsewhere.

Thank you @Old Guy , I have a brand new eacv and also fast idle valve (idle issue before now fixed ) so I don’t think that’s the issue, but I’m yet to test / replace the ecu coolant temp sensor I’ll let you know how I go many thanks for your help I’ve learnt a lot!

 

[PeterGrey]

Hi guys, sorry to bump into the thread randomly but this an only discussion online I found similar to the problem I have. As a couple of guys here, my car has a very rough idle after a warm start (either if it's just warm weather outside, or the car has been driven in the past 3-4 hours). It's a 2009 Peugeot 207 VTi.

What's weird about my problem is that the car starts, idles rough (computer says it has missfires on random cylinders) but if I immediately turn it off and back on, it just runs as normal most of the time, although sometimes it will lose throttle randomly in the first minute or so. After that it runs as normal. This only happens when the temperature is warm, like over 20C here in europe. In the winter, it starts up and works perfectly.

I had a feeling it might be something to do with the temperature sensors but now I've read it could also be the fuel lines, injectors or fuel pump. What could the most probable cause with my symptoms? Thanks in advance!

 

[Old Guy]

Peugeot 207? Aside from the fact that this is an NSX forum, Peugeot stopped selling cars in North America in 1991. I don't think you are going to find anybody on a North American based forum for any car who can provide informed advice on a Peugeot.