87S4..SMAF..42lb injectors.

Would a single leaky injector render a car "unstartable" when warm/hot?

My car starts fine when cold but I have a nagging hot /warm start issue that i cant figure out. Nothing has change in my Sharktuning in the time period this started and my cranking pulse width is inline with what others have with 42lb injecotrs. I have had my SMAF checked, i just got a rebuilt LH...and i have checked and swapped a Temp II sesnor.
I did a leak down and those results are fine also.

I have a fuel pressure gauge on the car and i dont see any appreciable drop in fuel pressure bewteen start attempts. Im actaully not even sure if a leaky injector would cause a noticable pressure drop?

I can start the car when its cold..let it idle for a minute or two, shut it down....then it wont start.

This problem cropped about 8 months ago. I pulled into a gas station to fill up came out and it wouldnt start....it has been like that now for a while and ive basically been living with it via a switch in line with my fuel pump. I discovered that if i kill the fuel pump, crank the car, it clears then starts and i simpley turn the pump back on again. Crued, but it works......but its getting old as you can imagine. Very similar to starting a flooded airplane engine. Based on this and other things, i feel the car is flooding in a very short period of time or is too rich at start. I ruled out vapor lock as this will occur with in minutes of the car being started for the first time in the morning for example

Since i havent changed anything on the car, im starting to lean towards a bad injector...or perhaps more?

I would figure the other cyclinders should atleast fire or sputter during start, but they dont.....until the fuel pressure drops (with my pump off) and the engine clears itself...then she fires right up and runs fine.

any leaky injector experiences?

 

It certainly has all the symptoms of an over-rich condition. But a leaky injector would be unlikely to prevent a restart in such a short time interval. I assume you mean switch off then try to restart imeadiately ? So o difference in engine temp between the two starts ?

What have you set injector opening time to, and what is cranking fuel pulse width ?

If you give it a footfull of throttle, will it start ?

 

I had leaky injectors on previous S4, cured by a new Ford set.

As JDS says your symptoms do not match an injector leak. I could always start immediately after shutdown. Problem was with warm starts when engine had been left for 30 minutes or more, after which time the leaking injectors had enough time to have flooded cylinders.

With leaking injectors you should fail the fuel pressure tests in the manual. I was losing a lot more than the 0.5bar allowed in the 20 minutes after pressurising system (from memory - may have the exact parameters wrong but I was failing test). Since you have a FP gauge good start would be to work through the wsm tests which distinguish between problems caused by the fuel pressure regulator, check valve at fuel pump, and leaking injectors.

 

have you pulled the vacuum lines off of the dampers and the FPR to see if any might be leaking??
Has the ISV ever been replaced??.
From its operation if its old then there is a good chance that it has a worn slip ring and it could be getting stuck in the closed position

 

From the Workshop Manual, Page 24-115, on testing the Temp II Sensor:

"In case of interruption (inf. Ohms):
excessively rich mixture, engine will not run in warm state and cannot be started."

Perhaps a broken wire or poor connection that interrupts the Temp II sensor circuit to the LH ECU intermittently?

 

Tony, have you tried data logging with a ST when trying to restart ? That should show a problem like intermittant Temp 2 as Wally suggests.

 

I agree - not the classic pattern for leaky injectors.

Log the restarts with ST and/or look at your wideband readout. Do you get a black exhaust cloud when it finally starts?

 

Thanks guys...
Ill check that stuff. Im heading out to put the plugs back in(from the leakdown test last night) and start it from cold. I'll data log the cold start, then the warm start afterwards.

Ive checked the temp II sensor at both the sensor and the pins to the LH and EZK, continuity and the results seem ok.
The injectors are NEW ford..been in the car for a few years now.
I will check the vac lines on the regulators...never thought of that one.
and the ISV appears to be in good order as i watch it on the Sharktuner screen.
When the car starts it idles fine as well as in other situations.

Ive ran into many little gremlins on the 928 over the years but this one is stumping the chump here!

below is a composite screen shot of where im at now on the parmeters and fuel maps...but as ive said, i havent changed anything on the map prior to this issue cropping up. So these settings should all still be "legit"and good for starting?.

 

My guess is a faulty Temp II signal, but here's what the WSM says could be the cause for poor hot start (in no particular order...)

1. Faulty Temp II (My bet)
2. Idle switch (Could also be the cause)
3. Injector circuit shutdown (Not likely)
4. Ground and plug connections (Not Likely)
5. Fuel Pump voltage (No)
6. Injector Valves/Control System (I think that German for LH)
7. Fuel Pressure (Bad Damper/regulator?)
8. Intake leaks (no)
9. Fuel Tank Venting (no)

 

Tony, I'm still only just over a week into tuning with an ST2 and 42lb injectors, but there is no way in hell my car would start when warm if I had that many 0's in the cranking fuel map. I have my injector size set to 36lb and my cranking pulse width is 3.20. I will post my cranking map when I get home.

I'm not sure why the car starts for you if you cut the fuel pump, but it couldn't hurt to try my maps before continuing.

To elaborate, I too was having fine cold starts but it would crank for over 10 seconds when trying to start when warm. Once I fattened up the cranking fuel map, it now starts perfectly when warm as well.

Dan
'91 928GT S/C 475hp/460lb.ft

 

Here is my current cranking fuel map:

104 92 68 56 46 35 24 16 14 13 13 9 5 0 0

Dan
'91 928GT S/C 475hp/460lb.ft

 

One should never lick one's injectors ... EVER

 

I've sent two sets of injectors here:

witchhunter

$19/ea plus $10 shipping. Quick turn.

They send back your injectors along with a report that includes before/after results. It'll perk up your old car.

I doubt it's a leaking fuel injector. That'll make it start with acrid gas smoke from the one piston. Or two. Or three. Even then it'll start and spin as the other cylinders fire.

 

Any reason i should see a discrepency between whats data logged on the LH vs the EZK for throttle postion?

During my first start this AM (which it FN didnt by the way) a few seconds into the start the EZK jumps to a throttle postion of "2" (cruise) while the LH data shows "1" idle.

The TPS checks out when i pull up the "fuel system monitor" screen and press the acclerator...

On the "igntion system monitor" screen it shows "cruise" and doesnt move when i press the accelerator.??

I tell ya what though, my poor battery is going to be toast when this gets solved!! Becasue of all this ive wired in a Hella quick disconnect instead of the wing nut....very handy for when you have to charge it several FN times a day !!!

 

I still have trouble with warm starts, but like Dan I have more cranking encrichment.

I'm still fiddling with it. It's tough to chase down, because you really only get one chance to crank the car. If it starts, great. If not, the next crank you're no longer dealing with the original state you're trying to correct. So it makes it harder to figure out whether it's too lean or too rich.

Not to thread hijack, but Dan what's the rationale behind setting 36lb instead of 42lb, when running 42lb?

BTW, I set my cruise map in open loop a fair bit richer to compensate for the leanout I was experiencing on warm days with a heat soaked engine. Now that it's cooler in San Diego, the o2 adjustment is maxing out at -20% on some cells, indicating the map is too rich to fully correct. Temps really seem to have a lot to do with variance in the AFR. Maybe this is obvious to everyone else, but it's something else for me to think about...I would think cooler, denser air would have to somewhat counteract having cooler, denser (?) fuel, but it definitely isn't a linear relationship.