Cold Start Stall

[FasNuf]

So I'm having an issue that I've been trying to figure out for a while. I've posted this on the HPT forum and want to post here as well for ideas.

Seems when the Coolant temp is under 50*F and the engine first fires off, it starts strong then after a second dies.
I attached a screenshot of the event. As you can see I have fuel pressure at the beginning and end of the log. My fuel pressure base is 43.5 psi. If you look at the white fuel pressure line on the graph, you can see it slopes down to 7 psi resulting in the injectors duty cycle to increase. This ultimately kills the engine.
My fuel system is a return system with a 1:1 boost regulator.

So things I've done to try to determine the cause.

1. Attached a power supply to the fuel pump directly to eliminate any electrical causes caused by relays or voltage drops. The power supply is variable voltage and capable of 30 amps at 14 volts. The pump is drawing 8 amps @ 13 volts in this screen shot.

2. Swapped the power supply to the other pump in my system to eliminate the pump as being the reason for the pressure drop. No change

3. Capped and plugged the boost reference port on the regulator just in case it was reacting strangely. no change there either.

4. Although its not seen in the scan, my AFR at startup is about .70 Lambda. This is a little rich, but not nearly enough to create a stall. The EQ commanded is what it is , commanded and not actual.

I cannot explain the sudden drop in fuel pressure on this mechanical system. The FPCM is basically used only for the NPP and fuel pressure sensor otherwise it doesn't control fueling pressure.

Any comments are welcome - Thanks

[dreksnot]

Mostly likely airflow or fuel related... Send me your tune and I'll take a glace at it.

[FasNuf]

Originally Posted by dreksnot

Mostly likely airflow or fuel related... Send me your tune and I'll take a glace at it.

Sent - Thanks

[eLeSthree]

I cant tell how your graph is plotted (cropped out of photo) but I do see a voltage drop occur and at the same time your FP dips. That makes me suspect a fuel system problem, and like you I would start troubleshooting there, but at the same time, why on earth would the ECM ever command .65eq?

Is this log from a cold start? If so, the engine is still in open loop, so fueling is based off of your tune. Once it gets running and goes into closed loop, does it command 1.0 and what are your fuel trims then?

[FasNuf]

Originally Posted by eLeSthree

I cant tell how your graph is plotted (cropped out of photo) but I do see a voltage drop occur and at the same time your FP dips. That makes me suspect a fuel system problem, and like you I would start troubleshooting there, but at the same time, why on earth would the ECM ever command .65eq?

Is this log from a cold start? If so, the engine is still in open loop, so fueling is based off of your tune. Once it gets running and goes into closed loop, does it command 1.0 and what are your fuel trims then?

The voltage is close to 14 volts right before the issue. The big dip before that is the cranking draw from the starter. I've looked at many other logs from other people and the control module voltage seems to dip quite a bit at cranking. Not to say this can't still be a problem because it can for sure. Dreksnot suggested looking at the alternator and whatnot. I haven't got a chance to go there yet, but things in the tune for Alternator seem fine. Battery is new and charged. If the car sits overnight above 50* or so, it still has the starting dip but starts without issue.

The fuel pump has been isolated from the car by powering with a power supply to eliminate voltage issues to the pump being the problem. I've swapped pumps and also capped and plugged the 1:1 boost reference line. The only thing in the fuel system that can change is the inectors or regulator. I find it strange that the regulator would only dip once in the cold being it's mechanical.
This only seems to do this below 50*F and after sitting at that temp for several hours. My cold start EQ is rich and is something I still need to work on. Once the car starts it's usually about .75 and .85 then gets to CL pretty quickly. It's probably seeing .65 from the over fueling the injectors are doing.
When the car is running at normal op temps. I'm 1.00 +/- 2% trims stay around 3% or so most days.
I've played with cold starting fueling and some of the spark tables too. I'm pretty stumped. I really dont want to buy a new regulator at $260 to find it's not the issue. The whole fuel system is about 9 months old with maybe 1000 miles. It's running 93 octane but the whole system is E compatible. Short of this starting hiccup, the car starts and drives great.
I'm starting to think this is an anomaly in my ECM that causes the spike causing the fuel pressure to drop because of the injector dumping fuel so quickly. I know it looks like fuel pressure drops first, but if you frame by frame the log and look at the PID's, the injectors fire before the fuel pressure, opposite what the graph shows. Strange, but I've graphed a bunch of these and some have 2 spikes of the injector DC/PW so that tells me it's a tune issue. The 2 spike log is really what's telling me it's not mechanical.
Where is the question.

Sorry, The forum wont let me upload the log, but the thread is located here. https://forum.hptuners.com/showthrea...ing-cold-start


Thanks for the comment. I appreciate the ideas. - Mark

[eLeSthree]

Originally Posted by FasNuf

The voltage is close to 14 volts right before the issue. The big dip before that is the cranking draw from the starter. I've looked at many other logs from other people and the control module voltage seems to dip quite a bit at cranking. Not to say this can't still be a problem because it can for sure. Dreksnot suggested looking at the alternator and whatnot. I haven't got a chance to go there yet, but things in the tune for Alternator seem fine. Battery is new and charged. If the car sits overnight above 50* or so, it still has the starting dip but starts without issue.

The fuel pump has been isolated from the car by powering with a power supply to eliminate voltage issues to the pump being the problem. I've swapped pumps and also capped and plugged the 1:1 boost reference line. The only thing in the fuel system that can change is the inectors or regulator. I find it strange that the regulator would only dip once in the cold being it's mechanical.
This only seems to do this below 50*F and after sitting at that temp for several hours. My cold start EQ is rich and is something I still need to work on. Once the car starts it's usually about .75 and .85 then gets to CL pretty quickly. It's probably seeing .65 from the over fueling the injectors are doing.
When the car is running at normal op temps. I'm 1.00 +/- 2% trims stay around 3% or so most days.
I've played with cold starting fueling and some of the spark tables too. I'm pretty stumped. I really dont want to buy a new regulator at $260 to find it's not the issue. The whole fuel system is about 9 months old with maybe 1000 miles. It's running 93 octane but the whole system is E compatible. Short of this starting hiccup, the car starts and drives great.
I'm starting to think this is an anomaly in my ECM that causes the spike causing the fuel pressure to drop because of the injector dumping fuel so quickly. I know it looks like fuel pressure drops first, but if you frame by frame the log and look at the PID's, the injectors fire before the fuel pressure, opposite what the graph shows. Strange, but I've graphed a bunch of these and some have 2 spikes of the injector DC/PW so that tells me it's a tune issue. The 2 spike log is really what's telling me it's not mechanical.
Where is the question.

Sorry, The forum wont let me upload the log, but the thread is located here. https://forum.hptuners.com/showthrea...ing-cold-start


Thanks for the comment. I appreciate the ideas. - Mark

Oh my bad, this log starts with engine off, I understand now.

May I ask, why you are using a base FP of 43psi? Injectors too big?

If you have a return style fuel system with a boost referenced mechanical regulator than the ECM has no control over FP anymore. The injectors are chasing the commanded .65eq, you said the wideband reads .70. The overfueling is caused by the tune.

If your FP is dropping to 7psi, and its mechanically controlled, you either have a regulator problem, voltage problem, pump problem, or flow problem. But it cant be tune related.

[FasNuf]

Yes, The base at 58psi was a little much for the injectors to control at idle. Idle wasnt stable enough for my liking so I lowered to 43.5psi. I bought a little bigger for future mods. I'm at 70% DC with E85 at redline with this setup.
Correct on the regulator, all mechanical and pretty much unaffected unless the injectors dump full wide open, then I guess pressure can drop before the mechanics respond which despite the graph I think is actually happening. It's not voltage to the pumps because that is supplied externally by my power supply. I capped the boost reference line just to keep the pressure stable. It was dropping to 36 psi because of engine vacuum and I wanted to eliminate that as a cause. I would think if it was a mechanical problem, it would happen a few times while trying to start instead of just once. This makes me think it's an anomoly in the tune causing the injectors to spike causing the drop in pressure until the regulator recovers. i just can't figure why the injectors would go that high and they especially wont fuel if it thinks I'm rich.
I'm going to see if I can keep the control module voltage up a little more during cranking and see what happens and check the alternator when I can.

Good thing is this ins't a huge deal because I don't normally drive in 30 deg. weather but it bugs me that it happens at all.

mark

[gtstorey]

Any chance this is a lack of fuel atomization due to low fuel pressure and cold temps causing pooling and then overly rich conditions?

[eLeSthree]

Which injectors? I assume you inserted all the injector data and scaled the tune if larger than 126#.

[FasNuf]

Originally Posted by eLeSthree

Which injectors? I assume you inserted all the injector data and scaled the tune if larger than 126#.

The injectors are FI Clinics 1200's

All the data is from the sheet they supply from their test. They flow under the 127LB/Hr limit of the ecm.

[FasNuf]

Originally Posted by gtstorey

Any chance this is a lack of fuel atomization due to low fuel pressure and cold temps causing pooling and then overly rich conditions?

At this point I cant rule much out.

[FasNuf]

For those interested, the issue was in the Transient Fuel Impact Factor Gas calibration.
I returned this table to stock and the cold stall resolved.