Got spark, Got fuel, no start. *TELL ME WHAT HAPPENED

Topic: Got spark, Got fuel, no start. *TELL ME WHAT HAPPENED (Read 3818 times) previous topic - next topic

Got spark, Got fuel, no start. *TELL ME WHAT HAPPENED

January 31, 2009, 09:02:10 PM

I hate it when you have spark and fuel but no start. Had my trailer full of fire wood for the mother in law and got in the Bronco (1990 351 efi) and cranked nice but no start.

I taped on the various relays thinking moisture might have a relay stuck,,,yeah right. Had the wife turn key while i stuck an ink pen in the shrader valve, yep got fuel. Pulled a plug wire and held it to the hood hinge,yep got spark.

I actually started thinking its just too darn cold out and its got something fugged up because it started just yesterday.

By now my gloves have been off for a while an i was freezing. Went and got the meter and turned on my key, yep i got my 5v source on the TPS. checked the green for less than a volt, nope i have 5v. Open tps.

The reason i posted this is because I feel something odd happened. I hooked up a spare TPS and let it lay to the side. I knew that if the tps was the problem then the truck should at the least start. Yep it started. OK, I gotta change this fugger but its not easy to get to, gotta take the whole throttle body off just to get to it since its the opposite of the 5.0 (on the bottome of the dual throttle body).

Just out of curiosity, I worked the trottle linkage. As sure as there is shiznit in a cat (thank for that one thunderchicken), it responded just as though it were mounted. Ok, Ill run this wood down to moms and just take it easy. Well The truck ran perfecly normal like nothing was wrong all the time the tps was hooked up but flopping in the wind so to speak.

I dont get it.

you thoughts anyone?

Got spark, Got fuel, no start. *TELL ME WHAT HAPPENED

Reply #1 – February 01, 2009, 12:37:32 PM

today I am going to try this on my 20th and see what happens.

Got spark, Got fuel, no start. *TELL ME WHAT HAPPENED

Reply #2 – February 01, 2009, 12:39:17 PM

My guess would be the pcm was in a "flooded engine" mode due to the shorted 5.0v reading it was seeing, thus killing injector pulse. It could start and run without a tps in fmem and possibly only affect thottle tip in and tip out which might not be noticeable when driving.
Maybe someone with more knowledge of the pcm's strategy could describe what exactly happened.

Got spark, Got fuel, no start. *TELL ME WHAT HAPPENED

Reply #3 – February 01, 2009, 12:45:03 PM

it never started or ran without a tps.

Got spark, Got fuel, no start. *TELL ME WHAT HAPPENED

Reply #4 – February 01, 2009, 01:00:49 PM

Maybe I misread the post. Are you saying the tps changed values while it was plugged in but not attached to the t.b. or that the truck just ran set up like that?
I'm not understanding "it responded"

Sorry,
Mike

Got spark, Got fuel, no start. *TELL ME WHAT HAPPENED

Reply #5 – February 01, 2009, 03:06:51 PM

what he was refering to is it ran with the tps just hanging there and not connected to the vehicle.

Got spark, Got fuel, no start. *TELL ME WHAT HAPPENED

Reply #6 – February 01, 2009, 03:25:56 PM

he unplugged to old tps, but didn't remove it, then plugged in a different one and just left it hanginng there.

Got spark, Got fuel, no start. *TELL ME WHAT HAPPENED

Reply #7 – February 01, 2009, 03:42:55 PM

Quote from: t.birdsc;254777

My guess would be the pcm was in a "flooded engine" mode due to the shorted 5.0v reading it was seeing, thus killing injector pulse. It could start and run without a tps in fmem and possibly only affect thottle tip in and tip out which might not be noticeable when driving.
Maybe someone with more knowledge of the pcm's strategy could describe what exactly happened.

This is what happened. The TPS has a "failure mode" that will let the car run without an operating TPS, but when stuck in 5V range, it thinks you're trying to clear a flood and cuts duty cycle (I'm not 100% sure of this, maybe 95%).

I understand there was a TPS hanging from the wires - even better as it wasn't out of range to start the car & warm it up with.

Got spark, Got fuel, no start. *TELL ME WHAT HAPPENED

Reply #8 – February 01, 2009, 04:51:59 PM

Quote from: Cougar5.0;254800

This is what happened. The TPS has a "failure mode" that will let the car run without an operating TPS, but when stuck in 5V range, it thinks you're trying to clear a flood and cuts duty cycle (I'm not 100% sure of this, maybe 95%).

I understand there was a TPS hanging from the wires - even better as it wasn't out of range to start the car & warm it up with.

Correct. Just like you would try to clear a flooded engine on a car with a carb with the throttle wide open. The pcm cuts off injector pulse because it believes the throttle is wide open. This could be the strategy this particular pcm has but others may not act in that fashion. I wish I knew more about what was going on in the pcm. Would my knowledge improve if I started using a tweecer?

Thanks,
Mike

Got spark, Got fuel, no start. *TELL ME WHAT HAPPENED

Reply #9 – February 01, 2009, 05:08:18 PM

Quote from: t.birdsc;254807

Would my knowledge improve if I started using a tweecer?

Thanks,
Mike

Yes. The TwEECer requires that you understand basic stuff about how the ECU does things. Then when you think you have learned something, you can get into arguments with the rest of us EEC geeks over at eectuning :rollin:

Got spark, Got fuel, no start. *TELL ME WHAT HAPPENED

Reply #10 – February 01, 2009, 06:16:32 PM

cougar8775 and haystack,, excuse me while i try to re-explain.

Cougar5.0 and t.birdsc,,trying to shorten my post one just for you all.

-truck cranked but no start
-I had fuel and spark
-found 5v on the green tps wire (bad reading, open tps)
-unplugged bad tps
-plugged in spare leaving spare just hanging to the side
-cranked and truck started.
Not only did it start but it responded to throttle normally as though it were mounted. I was able to drive without any problems.
Later i pulled the trottle body and changed the tps so i could actually mount it.

Also, i had to oblong the mounting holes with a chainsaw file to make the TPS adjustable in order to get .6v on the green wire.

I want to know why did the truck run and respond to throttle when it had nothing that I know of deciding what my trottle position was?

Got spark, Got fuel, no start. *TELL ME WHAT HAPPENED

Reply #11 – February 01, 2009, 07:41:18 PM

Quote from: jcassity;254817

Cougar5.0 and t.birdsc - trying to shorten my post one just for you all.

-truck cranked but no start
-I had fuel and spark
-found 5v on the green tps wire (bad reading, open tps)
-unplugged bad tps
-plugged in spare leaving spare just hanging to the side
-cranked and truck started.
Not only did it start but it responded to throttle normally as though it were mounted. I was able to drive without any problems.
Later i pulled the trottle body and changed the tps so i could actually mount it.

Also, i had to oblong the mounting holes with a chainsaw file to make the TPS adjustable in order to get .6v on the green wire.

I want to know why did the truck run and respond to throttle when it had nothing that I know of deciding what my trottle position was?

What you saw is expected behavior - at least for the ECUs I'm familiar with. If the ECU thinks you are at WOT during crank, it thinks you're trying to clear a flooded engine and provides no injector pulsewidth, fuel pressure or not.

Quote

CRKFLG = 1 ----|
------------------|AND ------------| BGFUL1 = BGFUL2 = 0
APT = 1 --------|
(Wide Open
Throttle)
-------------------------------------| --- ELSE ---
...

Once you changed to a different TPS and the engine is started, the FMEM (failure mode) routine will recognize the failed TP Sensor and use the MAF input to determine when the throttle opens. As stated above, there is no acceleration fuel (AE fuel), so the engine might be a little sluggish when you step on it.

Quote

FAILURE RECOGNITION

The FMEM strategy checks the "Continuous Self-Test Code" Filters to ascertain
whether a sensor has failed. If the sensor failure lasts long enough to
trigger a Self-Test Code, the FMEM strategy will substitute an alternate
value and strategy. Until the Self-Test filters exceed their fault
thresholds, the strategy continues to use the last known valid value.

Quote

The TP sensor Update logic substitutes a function of MAF for a failed TP
sensor. This action permits recognition of the various throttle modes
(Closed, Part or WOT). However, AE fuel will be disabled due to lack of TAR
signal.

Note that failure mode for the TPS at idle is 0.5 < TP < 1.25Volts (at least on the Ford ECUs I know). Setting the TPS very close to the lower limit like you did (0.6V) could be risky - most people will set it closer to 0.9V, which is where it should be without opening up the holes.

Got spark, Got fuel, no start. *TELL ME WHAT HAPPENED

Reply #12 – February 01, 2009, 07:56:32 PM

He also has no MAF...

Got spark, Got fuel, no start. *TELL ME WHAT HAPPENED

Reply #13 – February 01, 2009, 08:04:16 PM

Quote from: Haystack;254826

He also has no MAF...

If it's speed density, I would assume that they use the equivalent to the MAF for speed density - the MAP sensor.

Like I said, I don't know what ECU he is using, but FMEM is standard on fuel injected cars to allow for failed sensors.

Got spark, Got fuel, no start. *TELL ME WHAT HAPPENED

Reply #14 – February 01, 2009, 09:24:01 PM

Engine is speed density eeciv.

Mounting the unmodified tps would have put me at 1.45vdc wtih throttle closed. I actually have about .8v on the tps now.

I did not add in post one the blink test i did as well. Injectors were firing during the time the engine would not start. It was also very obvious the engine was flooding due to the smell under the hood and at the tail pipe.

what part of "OPEN" tps did you miss. I read the defective (unpluged) tps from the black wire to the green wire and got about 2M ohms.

When I saw 5v on the green,, I knew there was a problem. It was pretty obvious I was getting fuel to the cylinders also because of the gas smell out the tail pipe and up in the engine.

This might conflict the theory.