any car guys here? 99 mustang v6

[lilshawn]

I'm normally a pretty analytical guy...but I have an issue with a car engine for about a month that's been leaving me stumped.

my niece got a car given to her by a friend she met at a car meet. 1999 ford mustang V6. I was told this car was running normally, then one day they went out to start it...and it would not. they had other cars (as car meet people do) so they just used the other car and they just had this one sitting in their driveway.

they where going to just call auto scrappers to come get it, but after talking to my niece (who also has a 99 v6 mustang) she said that she could just have it (use it for parts or whatnot) so we get it towed to my house.

just for poops and giggles, I throw a battery in it and try and start it. stinks real bad of fuel after a few tries. no spark? nope... it has spark on all 6. means the crank sensor and coil pack are fine... stinks like fuel so it's getting gas.

pull out the plugs (soaking wet with fuel) and clean them off with some brake cleaner and the pressurized air hose... hit the key and after a few cranks it starts. it's miserable at the start... but soon straightens out. (probably excess gas in the cylinders)  as it warms up it comes about to run pretty good actually. idles okay. stumbles a little bit if you rev it while cold... but gets better as it warms up to operating temp. (typical computer relearning fuel stuff as the battery was not in it.) so I drive it around the block a half dozen times. seems to run pretty good. drives straight. has lots of piss and vinegar. feels like it has an upgraded clutch. park it for the night.

next afternoon I jump in it to move it to a different spot in the driveway. wont start, try 3 or 4 times but it smells flooded again. (try the old floor it wide open throttle to get the computer to cut fuel to clear it but no avail) abandon idea come back to it a couple days later.

hit the key a few times... still no start. pull the plugs... wet again. clean them out. same thing as the first time... miserable at the start...straightens out once warm. (clearing fuel again) runs good again

hook up to the computer. MAF reading properly. O2 sensors are reading, but short term fuel trims reading super rich so it's pulling TONS of fuel out to compensate. like it's getting all sorts of extra fuel from somewhere but can't figure out where.

shut car off. leave it for a few minutes, starts back up just fine. about half an hour. starts okay. an hour... it's a tough start but it does start. overnight. nope.

so I've been watching fuel pressures...40 to 43 psi and it looks stable even when revving... shut car off. watch pressure... stays about 40 so i don't THINK it's bleeding past injectors... and the regulator seems to work... none of the hoses for the EVAP system look like it has any raw fuel in them getting sucked into the intake.

any ideas where this excess fuel is coming from? maybe the injectors ARE partly clogged... but open? enough to slowly bleed excess fuel from the rail into the cylinders overnight? is that a thing? it's the only thing i can think of. wish i had a physical gauge i could put on the fuel rail to monitor it as it's was parked.

[Falken Hawke]

Does the fuel pressure regulator have a vacuum line connected to it? Typically, the fuel pressure isn't constant from idle to WOT and is reduced with engine vacuum (idle-part throttle).  Make sure there is vacuum and the line is tight.  If it checks good, the regulator is stuck.

If it doesn't have a vacuum connection and keeps constant pressure, then I'd consider looking at the injectors.  The computer pulling fuel would hint this shouldn't be the case though as the Fuel Map would be set to reduce fuel flow and the O2 sensor would fine-tune.

There are cheap testers out there that pulse the injectors and come with a plastic manifold that attaches to a can of carb/throttle body cleaner and an injector for cleaning and pattern inspection.  With a graduated cylinder, one could also flow test.

[lilshawn]

thanks for the reply! it's good to get a different set of "eyes" on a problem.

Does the fuel pressure regulator have a vacuum line connected to it? Typically, the fuel pressure isn't constant from idle to WOT and is reduced with engine vacuum (idle-part throttle).  Make sure there is vacuum and the line is tight.  If it checks good, the regulator is stuck.

it does have a pressure transducer/regulator combo on the fuel rail that feeds data back into the computer for fuel rail pressures. and yes, it does have manifold vacuum feedback.  I can bleed off the fuel rail pressure, and the computer reports the fuel rail pressure as zero, then upon priming the system before startup, it increases to 40 something PSI. as far as I can tell it's operating as designed. multiple primes does not seem to result in any higher pressures.

If it doesn't have a vacuum connection and keeps constant pressure, then I'd consider looking at the injectors.  The computer pulling fuel would hint this shouldn't be the case though as the Fuel Map would be set to reduce fuel flow and the O2 sensor would fine-tune.

There are cheap testers out there that pulse the injectors and come with a plastic manifold that attaches to a can of carb/throttle body cleaner and an injector for cleaning and pattern inspection.  With a graduated cylinder, one could also flow test.

i was just poking around amazon and saw what you mentioned. i've seen the big huge machines with the pumps and flow tester things that do 4/6/8 at a time and whatnot for like 500 bucks before, but never really noticed the small kits with the tester box and the spray can adapter like you said till now. I'll have to add that to my tool arsenal sometime.

the more and more I think about it the more I think there is an issue with the injectors. all of them? and all at the same time? I guess if some bad gas got in there and jammed the valve up maybe they aren't closing properly or something... I'm just keen on exploring all the potential what if's before i shotgun a set of injectors.

looks like i can go to the auto wrecker and get a set of 6 injectors for 51 bucks.  can't hurt to try i guess.

[Falken Hawke]

The fuel pressure will be "max" with the engine off as there is no vacuum to the regulator.  To test with the engine off, apply vacuum with a pump and pressure should drop.

[bobbyb13]

Falken Hawke is more intimately familiar with this particular vehicle than I am, but does it have a dedicated cold start circuit/injector or is it utilizing the regular injectors and/or some temporary change to the throttle plate position, air bypass valve or something else to enrich on a cold/cold start?

I have seen so many different ways that cold start enrichment was achieved that I wouldn't know where to start without staring at the engine.

It could even be duty cycle of the injectors and they are working fine but the computer is screwing it up by sending wrong values.

Not sure where Ford was at in '99 with this stuff.

[danny_galaga]

I can't believe they were going to scrap it when it wouldn't start without at least trying to get it going again...

[Mike A]

99 Mustang V6?

I see the problem. It is missing 2 cylinders.

[RandyT]

Is the gas stale?  How long was it sitting?  Water in the fuel could prevent a start and the miserable running at the onset could just be the engine choking it through when it does.  Increased fuel could be the result of the system trying to compensate for the poor burn.

Definitely a weird problem.  Spark+fuel almost always equals ignition, unless it floods before it gets to that point or there is no air.  Excess fuel delivery could be computer/sensor related.  Given that it was a "muscle car" in the day, I wouldn't discount the possibility that things were meddled with at some point either. 

[Zebidee]

I have some experience with pulling apart old cars with carburetors, but almost zero with fuel injectors and car computers... however it seems that the idle fuel/air mix is wrong. This is a problem that will seem to go away when the engine is warm. Explains the flooding you get.

If it isn't the computer, then it could be in the fuel line somehow - regulator/pump/filter. Oh, make sure there is sufficient air flow too, so check/clean/remove/replace the air filter.

Randy's point about stale fuel is worth considering too - maybe worth putting a gallon of fresh juice. I had a similar problem earlier this year, trying to get my old 1999 Holden Rodeo ute started again after it'd been sitting for 3-4 years (due to COVID travel restrictions).

[lilshawn]

sorry for not updating here. i haven't had a chance to look at the car again since my initial post. since then, i was involved in a fairly serious car accident, so between dealing with insurance and doctors, i haven't felt much like moving...let alone pull wrenches.

nevertheless... i'm quite the opposite. i can't figure out carburetors but can deal with computers just fine. carbs are magic to me. farting around with orifices and needles... sounds like bad party time for me.

the weird thing about the whole fuel injected engine thing... is that on starting, the computer essentially flies blind dumping fuel in with the injectors at a set programmed rate, which should be JUST enough fuel to get it going till the engine catches and the other sensors start coming to life and it can start adjusting things since it can now "see". this happens about 200 revs in. (this is typically why you experience a settling of the engine after about 5 to 10 seconds after start, its switching from going blind, to working with the sensor data)

seems to me that there is just excess fuel entering the intake somehow... flooding out the plugs before that happens. and I'll explain why i think that.

the thing is... the problem doesn't "go away" when it's warm... it's issue is being masked by the computer doing all kinds of things to the fuel system to compensate to keep the engine running. in this case... it's pulling most of the fuel out (IE shortening the injector pulse time to spray less fuel) and it's still reading that the engine exhaust is way rich.

this shortening of the injector pulses is called "fuel trim" and it uses a long term (average over the last drive cycle(s)) and short term (calculated on the fly as the data regarding the exhaust enrichment state comes in.) to determine how long to keep the injector open and spray fuel for to keep that juicy juice ratios good. so if the LFT (long fuel trim) is at -1% and the SFT (short fuel trim) is at -3% the injector timing is reduced  -4% to hopefully get the rate around 0 (i say -/+10% is fine.) when it make the adjustment and the fuel reads good for a bit... the SFT is added to the LFT so the long is now -4 and the short is about 0.

these percentages are calculated by a fuel map... a series of data points where the factory has said at this RPM at this temperature, at this engine load... you need to keep the injector open for this many milliseconds to achieve the perfect air fuel ratio.

if we have to ADD (+) fuel to this number... maybe our fuel filter is clogged a little... maybe the pump is weak.... injectors plugged up with gunk... maybe there is a vacuum leak and excess air compared to fuel is getting in and we have to dump in more fuel to compensate for this excess air.

if we have to PULL (-) fuel to this number... maybe out air filter is clogged... maybe the throttle body is not working properly. maybe an injector is stuck... excess fuel compared to the air coming in is off balance. we have to take out some of the fuel to compensate.

we don't seem to have excess air, we seem to have excess fuel (as evidenced by the flooding on startup)

so in this case, when the engine is running we get somewhere around -20 on the SFT and about -24 on the LFT so it's pulling -44% out of the injector pulse time or almost half when it is running. is is WAAY more that what you'd expect. (+/-10% total)

so the excess fuel is still there when it's running and it's just being mostly compensated for by the computer fuel trims only putting in a tiny bit of fuel that it would "normally" use as defined by the factory in the default fuel map and the adjustments to the LFTs and SFTs. it's getting closer, but not close enough to get the air fuel ratio in line with what it wants. eventually this car will throw a code saying "bank 1/2 too rich" or the like.

I don't THINK the gas is stale. it only sat a couple months. (maybe 5 months tops) the tank is about 1/2 full. it appears to be a fair weather driven vehicle so it wasn't run in the winter or anything like that. so it would have failed sometime this spring/summer.

I have a plan to pull the fuel line and take a sample and see if it's nice and clear or if it's discolored with varnish or chunky looking. i have pushed the schrader valve on the rail and had fuel come out (initially checking for fuel pressure) it didn't seem odd to me, but i'll probably take a bigger sample and see. maybe it has crap in it or other evidence that the injectors are indeed the issue. i don't know if these injectors are serviceable in any way (some can be back flowed with cleaner while energised to clear out stuff)

otherwise i might just throw a set of junkyard injectors in it and see what happens.

[bobbyb13]

Yeesh.
Hope you are doing ok.

As regards the Pony car, it wouldn't be the first time that injectors stuck open from contamination.
Maybe...
Drain tank.
Add fresh fuel with a dose of methanol fuel dryer.
Change filter
Swap in rebuilt injectors.
https://m.motormanfuelinjection.com/contact.html

If those injectors are failing then some crap in the fuel caused it at some point.
That would be my approach anyway.

Best of luck in recovering from that accident!

[lilshawn]

i do have a borescope camera. maybe if i can get into the intake and see an injector... hit the key to on and prime the fuel rail and see if it's dripping fuel out of the injector(s).

[Falken Hawke]

Everything you've described points to the pressure regulator being stuck open.  Apply vacuum to the regulator, start the engine.  Pressure with vacuum should be significantly less than what you are getting now.

[bobbyb13]

Or better yet, listen to this guy because he knows these cars!

Everything you've described points to the pressure regulator being stuck open.  Apply vacuum to the regulator, start the engine.  Pressure with vacuum should be significantly less than what you are getting now.

[lilshawn]

thanks for your input all.

I'll probably take another stab at this next weekend here. got a couple things to look closer into anyways even if it's just throwing pasta at the wall and seeing if something sticks.