Are you getting any check engine lights?
Engine won't stay lit
- Thread starter Valhalla
- Start date
NSXASTY - The usual ones come on and go off when it starts. I hooked up my scanner and the usual codes were there and I cleared them all. But I will continue to get those codes because I am running AEM EMS Series II. It's possible the AEM took a crap but I have no way of detecting that. If it's something I can't fix (and it's looking more and more like that with each passing day) I'll have to flat bed it to Autowave so they can figure it out. They did the install and tune of the AEM.
If it is the AEM unit, it is not even a year old and may just take the warranty and upgrade to the new Infinity unit. But that is a pretty big if. I'm just hoping it's something small and stupid and I haven't thought of it yet. But I've replaced so many of the usual suspects, I'm running out of places to look.
If it is the AEM unit, it is not even a year old and may just take the warranty and upgrade to the new Infinity unit. But that is a pretty big if. I'm just hoping it's something small and stupid and I haven't thought of it yet. But I've replaced so many of the usual suspects, I'm running out of places to look.
In your initial post, you stated that the engine cranks, starts up, revs to about 1800 rpm and then dies. This suggests that the engine is getting both fuel and ignition, at least during the initial start sequence.
The NSX service manual provides the following description of the start sequence:
<!--[if !supportLists]-->1. <!--[endif]-->When the ignition switch is initially turned on (II), the ECM supplies ground to thePGM-FI main relay that supplies current to the fuel pump for two seconds to pressurize the fuel system.
<!--[if !supportLists]-->2. <!--[endif]-->Whenthe engine is running, the ECM supplies ground to the PGM-FI main relay that supplies current to the fuel pump.
Since you have upgraded the fuel pump and removed the fuel pump resistor, I am going to hazard a guess that you have removed or bypassed the fuel pump relay and are running the fuel pump directly from the FI main relay – so we can eliminate the fuel pump relay as a potential problem.
Since your engine starts and then dies, I am going to speculate that the fuel pump may be getting the initial 2 second turn on prior to cranking which pressurizes the fuel line, the engine then starts during cranking but the FI main relay is not getting ground through the ECM once the engine starts running and then dies from absence of fuel. The best way to check this would be to measure the pressure in the fuel rail. If the fuel pressure falls immediately after the engine starts you know that the fuel pump is not being energized after start up (or you have aspectacular blockage in the fuel line, which I doubt since you did have a period where the car was working for a while). In the absence of a fuel pressure measurement, you could check the voltage at the fuel pump to see if you get the initial 2 second on when the ignition switch is turned to II, then see if the fuel pump gets power (briefly) after the engine starts and then dies. Measuring the pressure at the rail would definitely be the more definitive test. A pressure measurement would also identify problems with the fuel pressure regulator (or its setting) which could be causing a fuel starvation problem.
If the fuel pump is getting power after the initial start (or you are maintaining fuel pressure), then I am at a loss as to your potential problem. If the fuel pump is not getting power after the initial start it suggests that there is a problem with the ECM or its related systems (might be no tach signal – but I think that would prevent the initial start-up since the ECM needs a tach signal for ignition).
The preceding comments are based upon the operation of the OEM ECM. You stated that you had an AEM ECM; but, I am going to hazard a guess that the AEM will replicate to some extent the start-up sequence in the OEM ECM.
The NSX service manual provides the following description of the start sequence:
<!--[if !supportLists]-->1. <!--[endif]-->When the ignition switch is initially turned on (II), the ECM supplies ground to thePGM-FI main relay that supplies current to the fuel pump for two seconds to pressurize the fuel system.
<!--[if !supportLists]-->2. <!--[endif]-->Whenthe engine is running, the ECM supplies ground to the PGM-FI main relay that supplies current to the fuel pump.
Since you have upgraded the fuel pump and removed the fuel pump resistor, I am going to hazard a guess that you have removed or bypassed the fuel pump relay and are running the fuel pump directly from the FI main relay – so we can eliminate the fuel pump relay as a potential problem.
Since your engine starts and then dies, I am going to speculate that the fuel pump may be getting the initial 2 second turn on prior to cranking which pressurizes the fuel line, the engine then starts during cranking but the FI main relay is not getting ground through the ECM once the engine starts running and then dies from absence of fuel. The best way to check this would be to measure the pressure in the fuel rail. If the fuel pressure falls immediately after the engine starts you know that the fuel pump is not being energized after start up (or you have aspectacular blockage in the fuel line, which I doubt since you did have a period where the car was working for a while). In the absence of a fuel pressure measurement, you could check the voltage at the fuel pump to see if you get the initial 2 second on when the ignition switch is turned to II, then see if the fuel pump gets power (briefly) after the engine starts and then dies. Measuring the pressure at the rail would definitely be the more definitive test. A pressure measurement would also identify problems with the fuel pressure regulator (or its setting) which could be causing a fuel starvation problem.
If the fuel pump is getting power after the initial start (or you are maintaining fuel pressure), then I am at a loss as to your potential problem. If the fuel pump is not getting power after the initial start it suggests that there is a problem with the ECM or its related systems (might be no tach signal – but I think that would prevent the initial start-up since the ECM needs a tach signal for ignition).
The preceding comments are based upon the operation of the OEM ECM. You stated that you had an AEM ECM; but, I am going to hazard a guess that the AEM will replicate to some extent the start-up sequence in the OEM ECM.
Old Guy - Great thoughts and I followed this very closely. Went through the system last night to check all grounds and feeds. Everything seemed to be tight and connected. I do have a gauge on the dash for fuel pressure. I am running 45 - 50 psi, after the filter, and it stays there so the fuel starvation issue (which it sure feels like) just doesn't match up. Looks like it's going to be loaded on a flatbed and off to Autowave. Thanks for your input.
I'll post up what they find and what the fix is when I get her back.
I'll post up what they find and what the fix is when I get her back.
Mystery has been solved. The wires running to the fuel pump got so hot, they fused together and shorted. This was caused by the fuel pump pickup bottoming out in the bottom of the fuel tank and straining too much to flow at the proper psi. I am replacing the fuel pump just to make sure as the previous one has been straining for who knows how long. Should be up and running soon. Too bad I won't be able to drive it for at least 4 weeks due to right shoulder surgery. At least the car will be ready for me when I get my wing back. Thought you all might like to know the fix. Thanks to all for your suggestions and input.
Edit
OK so I got the final final tonight. The pump I got was NOT a Walbro 255 even though I ordered one, the invoice read one and the box said it was one. Be careful when ordering. The new pump is indeed a Walbro and has been wired to it's own relay. And it pumps a bunch. 58# at the fuel rail at idle so the MAP had to be reset. Also the wiring kit on the original package had shrink tubes on the connectors in the tank. These rotted away from the gas and the extra amperage and restriction of the flow caused these to rot away and expose naked wires in the gas tank. I got lucky that it shorted out and didn't start or run. Be aware or those selling Walbro's and buy carefully. I thought I had.
Edit
OK so I got the final final tonight. The pump I got was NOT a Walbro 255 even though I ordered one, the invoice read one and the box said it was one. Be careful when ordering. The new pump is indeed a Walbro and has been wired to it's own relay. And it pumps a bunch. 58# at the fuel rail at idle so the MAP had to be reset. Also the wiring kit on the original package had shrink tubes on the connectors in the tank. These rotted away from the gas and the extra amperage and restriction of the flow caused these to rot away and expose naked wires in the gas tank. I got lucky that it shorted out and didn't start or run. Be aware or those selling Walbro's and buy carefully. I thought I had.
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Thanks very much for sharing the fix with us. Can I ask which part did the wires fused together? It goes w/o saying that a "rewire" is necessary but the question is.. starting from where? We don't want to have to drop the tank for a rewire if it can be avoided (probably not though)
Thanks again. Very helpful post. Hope surgery goes well my friend. Be glad you have power steering!
Thanks again. Very helpful post. Hope surgery goes well my friend. Be glad you have power steering!
The wires fused at the connector outside the tank so it will be rewired. It's my right shoulder so I can't shift! Thanks for the well wishes.
The tank needed to be dropped anyway to install the new fuel pump.
The tank needed to be dropped anyway to install the new fuel pump.
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That is why I couldn't find it. Replaced everything else so I should have many miles of trouble free and smile inducing smiles for miles to come.
It is good that you have been able to resolve the problem. I am not doubting the source of the problem (it would jive with the fuel starvation symptoms that you appeared to be experiencing); however, what has me baffled is how, as you noted in post #29, it was able to maintain a fuel pressure of 45-50 psi with the fuel pump terminals shorting together. C'est un myst'ere (excuse my non French keyboard)!
Thanks OldGuy for hanging with me on this. With my gauge install it reads while the motor is running. As soon as it stops, so do the gauges. So while it was cranking over, it was reading it's usual 45-50 psi, but as soon as it starved, it shut down and so did the readings. We are also going to mount this circuit with it's own relay so as not to fry any more wires. Hope to get her back today. Glad this issue is over and looking forward to a trouble free summer driving season.
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