FullBlowncustoms
I'm Awesome
on top of the TBI, complete unit or just spring change etc...
Truck won't start, need suggestions.
- Thread starter Beason
- Start date
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FullBlowncustoms
I'm Awesome
Also I have seen the TBI to manifold gasket go bad often... I have two types of gaskets, one is the paper? other I have is discontinued I think? has metal in it. AGAIN IDK if gasket is bad lean with air telling it it needs more fuel dumping it in? IDK... You never over tightened or cranked the bolts down on TBI did you? that would be bad.. Strange in part of video no fuel pressure? but used a longer hose? Or intermittent with bad ground? IDK just ideas shooting crap out LOL
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Watch the second vid the Guage was bad. Fuel pressure is fine.. Which makes this even weirder..
FullBlowncustoms
I'm Awesome
IDK, seems fuel reg? or interment with grounds? compression good, valves, lifters stuck, etc all 8 plugs look to read the same? Run it at night in COMPLETE darkness look for sparks EVERYPLACE for crossfire...
Sir,
I watched your videos, and here are some quick observations:
1) The spark plugs you removed are definitely showing a way too rich A/F
ratios. (You want to read the color of the porcelain under the electrode.)
By comparison, the spark plugs in these closed-loop computer controlled engines
usually run anywhere from a bone white to a light tan. If you follow this link
there's a spark plug reading chart that you can familiarize yourself with: (Spark Plug Comparison Collection)
Note: The link points to reply #102, which is a quick overview. If you
would like additional detail, then go on down to reply #106 in the same thread.
2) The fuel coming out of the Injectors during cranking is a lot. As in it's
trying to fuel an engine trying to start at -40°? In the TBI system, the
ECT sensor (Engine Coolant Temperature) has a lot of authority, and one
that is no longer working properly will cause the symptoms that you are
experiencing. (-40° = 100,000 ohms of resistance, while 266° = only *70* ohms)
I am currently searching for the temperature vs. resistance table that we can use
(along with an ohmmeter) to see if there's a gross problem with your
sensor. (Of course there could also be a wiring issue between the sensor
and the ECM, so getting the ECM to tell us what *it* sees (live data)
would be the no-kidding troubleshooting approach to prove/disprove this theory.)
3) The fact that you've been able to work around the issue by flooring the gas
pedal and putting the system into the "Clear Flood" mode again tells me that
we have too much of a good thing when it comes to fuel delivery during normal
cranking. (And if you watch the video closely when you floored it, notice the fuel
delivery cuts way back like it is supposed to.)
More in a minute, gotta go find that table.
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While we are waiting for me to find that table, here is where I pulled the
ECT info I shared above from. ('89 FSM)
Troubleshooting tips:
1) These have been known to lose their calibration, and create A/F ratio errors
during open loop operation.
2) The basic way the circuit works is that a calibrated +5v is sent to the sensor.
The higher the resistance, the higher the voltage that the ECU observes.
The lower the resistance, the lower the voltage that the ECU observes.
IF you were to have an open in the wire to this sensor, the ECU will read
all 5 volts, and you will get the -40° F rich air/fuel ratios. (!)
And IF you had that wire chafed/shorted somewhere, you would get the
lean 266° A/F ratios.
NOTE: A completely open or shorted circuit should result in a MIL light, but
as of yet it's too soon to go there? We first need to prove/disprove the ECT
sensor hasn't lost it's calibration.
More in a couple.
ECT info I shared above from. ('89 FSM)
You must be registered for see images attach
Troubleshooting tips:
1) These have been known to lose their calibration, and create A/F ratio errors
during open loop operation.
2) The basic way the circuit works is that a calibrated +5v is sent to the sensor.
The higher the resistance, the higher the voltage that the ECU observes.
The lower the resistance, the lower the voltage that the ECU observes.
IF you were to have an open in the wire to this sensor, the ECU will read
all 5 volts, and you will get the -40° F rich air/fuel ratios. (!)
And IF you had that wire chafed/shorted somewhere, you would get the
lean 266° A/F ratios.
NOTE: A completely open or shorted circuit should result in a MIL light, but
as of yet it's too soon to go there? We first need to prove/disprove the ECT
sensor hasn't lost it's calibration.
More in a couple.
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OK, I scoured the '89 FSM, and couldn't find it. (Trying to use the manual
that best matches your vehicle.) But since I know I've seen it, I jumped over to
the '95 FSM, and sure enough there it was:
OK. With an ohmmeter you can use the table to measure the resistance of the
ECT sensor to engine ground, using the ambient temperature of your shop
as the input to this table. For example, if your garage is at 50° F, then your
ohmmeter should measure in the neighborhood of 5670 ohms. If it's way off
then we need to get a good sensor installed and see what we now have.
****
To recap the last couple of replies, based on the coloring of the spark plugs, the
quantity of fuel being sprayed, and the need to use the Clear Flood function to
get the engine to fire, instead of a too little fuel problem, we seem to have too
much during cold cranking. Just as soon as you can make this measurement
and share it we should be able to figure out which way to go forward.
Best of luck --
that best matches your vehicle.) But since I know I've seen it, I jumped over to
the '95 FSM, and sure enough there it was:
You must be registered for see images attach
OK. With an ohmmeter you can use the table to measure the resistance of the
ECT sensor to engine ground, using the ambient temperature of your shop
as the input to this table. For example, if your garage is at 50° F, then your
ohmmeter should measure in the neighborhood of 5670 ohms. If it's way off
then we need to get a good sensor installed and see what we now have.
****
To recap the last couple of replies, based on the coloring of the spark plugs, the
quantity of fuel being sprayed, and the need to use the Clear Flood function to
get the engine to fire, instead of a too little fuel problem, we seem to have too
much during cold cranking. Just as soon as you can make this measurement
and share it we should be able to figure out which way to go forward.
Best of luck --
Re: Heavy fueling during cranking. Reading the troubleshooting section
of the '89 FSM they discussed the difference in air/fuel ratios commanded
during cranking based upon the Engine Coolant Temperature input.
It ranges from a (stoich) 14.7:1 A/F ratio at 201°F, all the way to a 1.5:1 ratio
at -33°F. (!) (See attached.)
Don't get me wrong, nothing beats a healthy computer
controlled engine when it comes to starting at sub-zero temps...but
if you happen to have a bad ECT sensor lying about the coolant temp
to the computer, some real fuel can be showered into the intake manifold
while cranking. (!)
****
Please keep the following in mind while troubleshooting this:
1) IF the ECM isn't securely grounded to the engine, then this
lack of ground (with a good ECT sensor) will still read as a high
resistance. And as we've recently read from the book, the
higher the resistance, the lower the temperature reported.
It's not just how tight the grounds are connected to the
engine, but the ground wiring needs to be in perfect condition
all the way from the engine to the correct ECM pins.
2) And once you've proven to yourself that the ECT is working
as advertised and you are *still* experiencing these issues, then
it could still be an issue with the ignition system. Others in this
forum have had their distributor cause similar symptoms. But
instead of the parts cannon, we should first prove/disprove the
ECT sensor functionality.
3) And once we get the truck starting reliably, we may or may not
still have to figure out why the truck dies at approx. the 5 minute mark?
If I had to guess I'd say that right around the time the engine goes
from open loop to closed loop that another issue gets involved via
the A/F feedback loop? (fouled O2 sensor?)
****
So far you have given the truck a good tuneup on the ignition side,
and also replaced the fuel filter. Both good maintenance. Also on
the positive side is that when it's running your engine sounds nice
and quiet, didn't hear any expensive noises.
That's all I've got for now. Let us know what you discover.
Fingers crossed --
of the '89 FSM they discussed the difference in air/fuel ratios commanded
during cranking based upon the Engine Coolant Temperature input.
It ranges from a (stoich) 14.7:1 A/F ratio at 201°F, all the way to a 1.5:1 ratio
at -33°F. (!) (See attached.)
Don't get me wrong, nothing beats a healthy computer
controlled engine when it comes to starting at sub-zero temps...but
if you happen to have a bad ECT sensor lying about the coolant temp
to the computer, some real fuel can be showered into the intake manifold
while cranking. (!)
****
Please keep the following in mind while troubleshooting this:
1) IF the ECM isn't securely grounded to the engine, then this
lack of ground (with a good ECT sensor) will still read as a high
resistance. And as we've recently read from the book, the
higher the resistance, the lower the temperature reported.
It's not just how tight the grounds are connected to the
engine, but the ground wiring needs to be in perfect condition
all the way from the engine to the correct ECM pins.
2) And once you've proven to yourself that the ECT is working
as advertised and you are *still* experiencing these issues, then
it could still be an issue with the ignition system. Others in this
forum have had their distributor cause similar symptoms. But
instead of the parts cannon, we should first prove/disprove the
ECT sensor functionality.
3) And once we get the truck starting reliably, we may or may not
still have to figure out why the truck dies at approx. the 5 minute mark?
If I had to guess I'd say that right around the time the engine goes
from open loop to closed loop that another issue gets involved via
the A/F feedback loop? (fouled O2 sensor?)
****
So far you have given the truck a good tuneup on the ignition side,
and also replaced the fuel filter. Both good maintenance. Also on
the positive side is that when it's running your engine sounds nice
and quiet, didn't hear any expensive noises.
That's all I've got for now. Let us know what you discover.
Fingers crossed --
Attachments
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Thanks guys for the detailed info!
I will try to find the ETC and test. I do have an ohm meter and some other electrical tools.
It looks easy to access, with a 2 pin harness. Do i just check ohm across the 2 pins?
I will try to find the ETC and test. I do have an ohm meter and some other electrical tools.
It looks easy to access, with a 2 pin harness. Do i just check ohm across the 2 pins?
