Warm start problem - fuel pump?

[E9Wayne]

Hey guys, just back from a wonderful weekend at the Vintage and about 50 of my closest E9 friends with many of their spouses too like Shawn Macha.

Anyway, on the way home my car experienced some pretty consistent warm start problems. Tom Baruch was with me when it happened on about three occasions and we verified that the engine is getting spark and she cranks well also. What cured it yesterday was spraying some starter fluid/carb cleaner through the idle control valve inlet into the log manifold.

Is this a sign my fuel pump is going? Not getting enough fuel to engine for a warm start, or maybe a Megasquirt setting? I've never had this happen before and the fuel pump is about 5 years old.

Cold start is fine and she idles well also.

Don Lawrence, my engine builder, thoughts?

Wayne

 

[lloyd]

You don't offer a lot of details, including the system you have in place. Mentioning "log manifold" and "megasquirt" indicates fuel injection, but not much more. It might be helpful if you pulled a plug or two the next time this happens and check for wetness.

I doubt the problem is with your fuel pump if it can supply the engine at a cold start and throughout the rev range. It takes consistent pressure for that to occur. You seem to be hinting at a vapor lock problem which is far more common with carburetor -equipped cars. This is generally not a problem with fuel injection since any vapor is purged almost immediately when the system is pressurized. That said, the fuel pressure regulator could be weak or out of adjustment, so that the heat somehow affects its ability to regulate pressure. The problem with this theory is that if the regulator is fickle enough to permit pressure changes when warm, it would most likely cause some other engine operation problems other than merely hot starting.

A hot start problem is often the result of a flooding condition that can occur when one more injectors leak fuel when sitting under pressure. The cold start injector is often the primary culprit, but any injector could be problematic. Since heat necessarily seems to be related to your symptoms, any electronics that are subjected to undue heat are suspect. That might even include temp sensors, that can cause the typical ECU to engage in default rich limp mode. A wide open throttle when starting may eventually clear things out and allow for a more combustible mixture. Starter fluid may, of course, help fire an engine with an overly lean or rich fuel mixture. Toluene-based carb cleaner, generally removes excessive carbon. Too much, and it can remove any top cylinder lubrication.

 

[E9Wayne]

Hi Lloyd, thank you for this diagnosis and it makes a lot of sense. I will check my fuel pressure regulator which is a Saab 3.5 bar rated unit. It is also interesting that the first time this happened, after about ten minutes of trying to start in cooler weather, I was told to floor the throttle and try again and it started immediately - thinking that this was a flooded system situation and releasing more air at WOT cleared things up. But this approach did not work the second time the symptoms occurred and that's when we tried the carb cleaner approach.

 

[Stevehose]

Did it do this on the way down to the Vintage too?

 

[E9Wayne]

Hi Steve, now that I think about it, there were one or two episodes when she didn't fire up right away on the way down...with the same symptoms - cranking was fine but symptoms of either flooding or not enough fuel - or spark. But these episodes only lasted 5 - 10 seconds each and varying the throttle seemed to resolve it.

 

[E9Wayne]

One more thing that Don or Sven might have ideas about. My car has bucked at low rpms off throttle since day one (before Megasquirt). I wonder if the 3.5 bar unit delivers enough fuel at low speed rpm and if I should upgrade to a 3.8 bar or more unit to cure this.

 

[lloyd]

One more thing that Don or Sven might have ideas about. My car has bucked at low rpms off throttle since day one (before Megasquirt). I wonder if the 3.5 bar unit delivers enough fuel at low speed rpm and if I should upgrade to a 3.8 bar or more unit to cure this.

I do not profess to know much about Megasquirt, but I doubt increasing fuel pressure has anything to do with your hot start problem, especially assuming that the pressure is adequate to supply the engine under load and at speed. Although not ideal, reduced pressure should suffice for starting and idling.

A little research suggests that at least some Megasquirt versions can be adjusted to address hot-lean-start conditions as well as hot-rich situations.

If the engine stays cranking for a while without catching, adjust the cranking pulse width setting at the temperature where you’re having this problem. It’s often best to start with what you think is not enough pulse width and add more in, since a flooded engine can take a bit longer to clear. A good rule of thumb to figure out which way to go is to try giving it a little bit of throttle and cranking it. If more throttle makes it easier to start, try less cranking pulse width. If it makes things worse, try more. Note that if you’re seeing zero cranking pulse width, you’ve probably triggered flood clear mode. Check your TPS readings, as having this go too high will shut down the injectors.

If you find you’re not getting anywhere with the throttle test, try pulling a spark plug after a failed start, and see if it’s wet with fuel or dry. If it’s wet, reduce the fueling; if it’s dry, add more fuel to the cranking pulse width.

Next, have a look at what happens after the engine catches. In this case, you’ll want to adjust the afterstart enrichment (ASE) by trial and error to keep the engine from stalling. You can try pulling a spark plug after a failed starting attempt to see if it’s wet with fuel (too much) or dry (too little). Give it whatever combination of ASE and throttle keeps the engine going (not necessarily idling – revving it to 1500 RPM to keep it from stalling can be a good idea on an untuned engine) until it warms up, then dial in the VE table with the engine hot, where ASE and warm up enrichment have shut down. Once you have the final values on these, you can dial in final values for warmup enrichment and ASE.

. . . . .

. . . . .

Lean idle on hot starts
If the engine runs lean and roughly after hot starts for about a minute or two, then settles to normal, check your air temperature sensor readings. Often, this is caused by sensor heat soak, where the sensor absorbs more heat from the intake manifold than the air does. There are several approaches you can take to fixing this.

• If using a closed element air temperature sensor, switch to an open element type.
• Sensors located in the intake manifold are especially prone to this – try relocating the sensor to the intake piping.
• Use the “Ignore MAT correction during ASE” option to turn off the air density correction for the time when after start enricment is active.
• Adjust the MAT correction curve to add more fuel at high air temperatures.

Too much fuel even with zero cranking pulse width
On some cars with very large injectors, you may find yourself having reduced the cranking pulse width to zero, and the engine is still acting like it has too much fuel. The reason is that the code is adding the injector dead time to the cranking pulse width, and if your dead time setting is high enough, it can be enough pulse width on its own to flood the engine. If this happens, reduce the injector dead time. Note that if you already have a fuel table dialed in, you will need to add more fuel in to compensate.https://www.diyautotune.com/support/tech/other/megasquirt-startup-tuning/

Low speed bucking could be due to any number of things, from a mixture that is too lean, to overly advanced ignition timing to being in the wrong gear at low speed. Not saying that your symptom is any one of these things, except that often the cure for a problem can be simple or deceptively simple.

 

[E9Wayne]

Thanks again, Lloyd. What is odd is that my car has never done this before this trip, which tells me it's more of a part issue that settings on my megasquirt table,


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[sfdon]

test your fuel system like this:

Next time you are out driving and the car is warm- turn the key on five times without cranking. 5 times in a row and then crank.
If no warm start problem anymore you have a lack of fuel in the rail problem

If the problem gets worse you have too much fuel problem

 

[E9Wayne]

Thanks don, I guess the next question is what I do in either case. If I don't have enough fuel is that a mechanical problem or something ms can solve through info Lloyd found?


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[sfdon]

One solution at a time grasshopper

 

[E9Wayne]

Thank you Master Po

 

[Ohmess]

Wayne -- if Don's test indicates you have too much fuel, which I suspect will be the case, I would look specifically at Lloyd's suggestion that you may have fuel leaking around an injector or two.

 

[E9Wayne]

Well guys, I went out to the car today to get it cold started and now that doesn't work either. Wide open throttle, Don's suggestion of five on cycles...nothing. I'm glad this didn't happen in Asheville. Clearly the problem was starting on the return trip and has only gotten worse.

 

[Stevehose]

You better get this sorted before you drive it to New Orleans in November

Well guys, I went out to the car today to get it cold started and now that doesn't work either. Wide open throttle, Don's suggestion of five on cycles...nothing. I'm glad this didn't happen in Asheville. Clearly the problem was starting on the return trip and has only gotten worse.

 

[sfdon]

Call me to tomorrow for a walk through

 

[sfdon]

Make sure you have a spare spark plug when you call

 

[Vern]

Nope. Nope. Nope. Let's back up the boat. Wayne, do you have Tuner Studio?

 

[Vern]

You don't offer a lot of details, including the system you have in place. Mentioning "log manifold" and "megasquirt" indicates fuel injection, but not much more. It might be helpful if you pulled a plug or two the next time this happens and check for wetness.

I doubt the problem is with your fuel pump if it can supply the engine at a cold start and throughout the rev range. It takes consistent pressure for that to occur. You seem to be hinting at a vapor lock problem which is far more common with carburetor -equipped cars. This is generally not a problem with fuel injection since any vapor is purged almost immediately when the system is pressurized. That said, the fuel pressure regulator could be weak or out of adjustment, so that the heat somehow affects its ability to regulate pressure. The problem with this theory is that if the regulator is fickle enough to permit pressure changes when warm, it would most likely cause some other engine operation problems other than merely hot starting.

A hot start problem is often the result of a flooding condition that can occur when one more injectors leak fuel when sitting under pressure. The cold start injector is often the primary culprit, but any injector could be problematic. Since heat necessarily seems to be related to your symptoms, any electronics that are subjected to undue heat are suspect. That might even include temp sensors, that can cause the typical ECU to engage in default rich limp mode. A wide open throttle when starting may eventually clear things out and allow for a more combustible mixture. Starter fluid may, of course, help fire an engine with an overly lean or rich fuel mixture. Toluene-based carb cleaner, generally removes excessive carbon. Too much, and it can remove any top cylinder lubrication.

Lloyd, this is a Megasquirt system. So if you don't have experience with it, conventional Bosch 1.1 or 1.3 knowledge is out the door. Bosch injection has hard parameters and a finite troubleshooting guide. MS is squishy with it's own parameters, including data logging, which literally speaks volumes.

There is a known MS problem with warm starting related to the alternator, which requires an in-line diode fix. In fact, it is a known BMW problem. I troubleshoot and deal with these issues specifically. And yes, a bad fuel pump ground or loose connection to the non standard fuel pump can cause an intermittent fuel issue.

 

[Ohmess]

Vern -- can you please describe the known BMW problem, along with the fix?