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Questions (TBI & Flooding)
- Thread starter Miller75
- Start date
4xcrazy
3/4 ton status
not sure where you were going with the coolant temp gauge, but the computer reads the temp of the coolant off the sensor on the intake, the gauge reads it from the one in the side of the head.
This issue has got me thinking, and from what i know, which sometimes isn't much, the only thing controlling fuel flow, would be the pump pressure, which is regulated by the pressure regulator diaphram in the TB unit, and the the signals the injectors get from the ignition control module for WHEN to pulse. The amount or pulse width pattern i believe is used for cold morning starts or choke setting, extended pulse for more fuel, should be controlled by the coolant temp sensor (in the intake) and also the o2 sensor. The O2 sensor though not too sure about causing this much trouble though, as i have actually had mine unplugged and it didn't really affect the way it ran, although the SES light did come on.
I've had alot of fixes, diagnosing and repairing in my time with this truck i have now, and would like to think i understand how most o everything works, however, just recently when i had my injector pulse problem, or lack of, i was informed by SCOTT
4X4HIGH,,, of the ignition control module actually controlling when the injectors pulse. Learned something else i had not had to deal with in the past, and thanks again Scott, so far it's still running 
.
Vacuum leaks and whatnot, from past experiances with "issues" on these things shouldn't cause the injectors to dump that amount of fuel down the intake, it will affect the way the engine rune, but these engines run alittle differently than a carb'd engine does, Heck even a bad coolant temp sensor should let the injectors "dump" fuel like you are describing, it would make the motor run alittle richer, but should still run without your issues.
I'm leaning on the pressure regulator in the TB unit, (somewhat cheap) and if that isn't the problem, i would be looking at the injectors,(gettin costly) and then head towards whatever controls the pulse width pattern possibly holding the pulse pattern open too long. (price unknown
)
of course it ALL gets controlled by the main computer too though
This issue has got me thinking, and from what i know, which sometimes isn't much, the only thing controlling fuel flow, would be the pump pressure, which is regulated by the pressure regulator diaphram in the TB unit, and the the signals the injectors get from the ignition control module for WHEN to pulse. The amount or pulse width pattern i believe is used for cold morning starts or choke setting, extended pulse for more fuel, should be controlled by the coolant temp sensor (in the intake) and also the o2 sensor. The O2 sensor though not too sure about causing this much trouble though, as i have actually had mine unplugged and it didn't really affect the way it ran, although the SES light did come on.
I've had alot of fixes, diagnosing and repairing in my time with this truck i have now, and would like to think i understand how most o everything works, however, just recently when i had my injector pulse problem, or lack of, i was informed by SCOTT
4X4HIGH,,, of the ignition control module actually controlling when the injectors pulse. Learned something else i had not had to deal with in the past, and thanks again Scott, so far it's still running .Vacuum leaks and whatnot, from past experiances with "issues" on these things shouldn't cause the injectors to dump that amount of fuel down the intake, it will affect the way the engine rune, but these engines run alittle differently than a carb'd engine does, Heck even a bad coolant temp sensor should let the injectors "dump" fuel like you are describing, it would make the motor run alittle richer, but should still run without your issues.
I'm leaning on the pressure regulator in the TB unit, (somewhat cheap) and if that isn't the problem, i would be looking at the injectors,(gettin costly) and then head towards whatever controls the pulse width pattern possibly holding the pulse pattern open too long. (price unknown
)of course it ALL gets controlled by the main computer too though
Jessie James
1/2 ton status
Apparently if the coolant sensor on the intake is not working then the TBI will flood. I did not realize there were two sensors. Perhaps he can test/swap the one on the intake?
4xcrazy
3/4 ton status
As mentioned before, i think the first thing to do is get the SES light fixed, if it's just a bulb that's out so to try to get the codes read. With that much fuel, and driveability issue, it HAS to be faulting out something.
If for some reason even with a new SES light, you still cannot get the SES to light up or flash, i would suspect a computer issue. I had a buddy awhile back with an '87 Burb that we could not get it to run right, couldn't get codes out of it, SES would never light up, don't remember the extact issues, but one day when i was not around, he replaced his computer and it worked fine fromthen on out.
I know/heard it's rare for a computer to die out, but it can happen, it's an electrical component.
If for some reason even with a new SES light, you still cannot get the SES to light up or flash, i would suspect a computer issue. I had a buddy awhile back with an '87 Burb that we could not get it to run right, couldn't get codes out of it, SES would never light up, don't remember the extact issues, but one day when i was not around, he replaced his computer and it worked fine fromthen on out.
I know/heard it's rare for a computer to die out, but it can happen, it's an electrical component.
4xcrazy
3/4 ton status
Are you reading this from a service manual or something, i'm curious, not bad mouthing or anything, i am wondering about this info because i am actually getting a SES light in my '94 for the knock sensor and the coolant temp sensor both, reset the computer, it lights back up within a couple of minutes, however, the truck is completely driveable, really don't feel any difference in the way it performs, maybe alittle lacking on performance i would gather due to the faulting knock sensor not getting the timing just right, but otherwise, i dunno...
Wondering about the parameters of this CTS, if one bad reading one way causes this flooding, and one bad way the other causes something else.
This is one thing i find interesting with these TBI motors, i love them for their reliability WHEN they are running properly, but sometimes they can be a little bit of a bear to finger out what's faulting out, when they do.
This sounds like a CTS problem. If the CTS fails, it looks to the ECM to be sub-zero temperatures. The ECM responds by dumping a ton of fuel into the TBI - if I remember right it is somewhere like a 1.5:1 AFR while cranking. Check the voltage at the CTS and look up what temp that coresponds to. It is a cheap and easy replacement if it comes to that.
4xcrazy
3/4 ton status
Still questioning this, mainly due to current experience/issues myself as previously mentioned with my '94. The CTS is faulting out, yet i have no flooding problems...
4xcrazy
3/4 ton status
and even still if it were to sense an ultra cold climate, coolant temp, whatever, it STILL should not be "dumping" fuel down the intake, it would only adjust the settings on the injectors, pulse timing to add more fuel, similar to a choke setting on a carb'd motor. It would definately richen up the fuel content, to a point, but no way should the computer allow dumping of fuel at any temperature.
British Slave
1/2 ton status
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If it is a TBI issue, this will lead you to the promised land:
http://www.73-87chevytrucks.com/techinfo/TroubleshootingTBISystems.pdf
http://www.73-87chevytrucks.com/techinfo/TroubleshootingTBISystems.pdf
smier
1/2 ton status
X2!!! The great thing about the ECM is it will often tell you or at least point you in a direction towards whats wrong. This is an early design so it's a little lacking in it's ability in comparison to newer on board diagnostics. If your check engine light doesn't work it could be trying to tell you somethings wrong and you wont know it.
@ Jessiejames- it doesn't matter to the ECM if his temp guage works or not for the computer, it uses 2 different sensors, one in the intake manifold for the ECM and the other is typically in the cylinder head to send the reading to the guage.
In theory something could be malfunctioning and telling it to run incredibly rich and just flooding the thing out. Have you been able to get it to start at all
after replacing the plugs? Don't forget the computer has to relearn how to run properly.
Jessie James
1/2 ton status
yeah, I have the 1990 TBI fuel and driveability manual. However, it's incredibly long and complex, with steps on how to test just about every single thing under the hood, so it's hard for me to give any step-by-step stuff, as each thing is so long. I love the brotherhood and all, but I just ain't typing all that in!
I Googled to see if I could find one for sale to point the OP too but no luck. I took me a month to find mine!
Anyway, besides the fact that the coolant sensor is listed first, the manual stresses that getting the service engine soon (SES) light to work should be the FIRST step so you can diagnose the codes. It says "The System Check is the starting point for the diagnostic procedures or an emissions test failure" Just like that!
It walks you through everything, putting it in diagnostic mode, etc., but I also put that in the K5 Buyers Guide which is stickied at the top of the main forum (link at the bottom of my first pots).
smier
1/2 ton status
That looks to be a great link, I'll be curious to take some time after work and thoroughly read thru it myself...
typically by replacing the plugs I can get it to start but that only last for so long
Jessie James
1/2 ton status
Okay, I hope this helps, I took photos of the first few pages of the Fuel & Emissions driveability manual for TBI trucks ...
...
Ok, I can't do that because the limit for zip files on the site is 97kb and the file is 5mb.
PM me your email address and I'll send it along.
...
Ok, I can't do that because the limit for zip files on the site is 97kb and the file is 5mb.
PM me your email address and I'll send it along.runs for a few mins then fouls out again right only reason i ask is because i had it happen 2 weeks ago and it was coolant temp sensor telling the comp it was -41 degrees out when it was 50 and man that thing put the fuel to it lol not sure yours is the same but thats what mine turn out to be
Jessie James
1/2 ton status
That's my guess too.
Okay, I hope this helps, I took photos of the first few pages of the Fuel & Emissions driveability manual for TBI trucks ...
...
Ok, I can't do that because the limit for zip files on the site is 97kb and the file is 5mb.
sent you a pm Jesse
Could anyone post a pic of where the vacuum lines plug into so I can verify they are connected correctly
DeviousK5
1/2 ton status
Your underhood emissions label should contain a reasonably good vacuum diagram. If its missing, go pick up a chiltons manual-you'll need it again one of these days
Jessie James
1/2 ton status
Miller75 I emailed those to you. Let me know if they don't show up.
My vacuum lines mostly came off the back of the TBI body. However, a quick twist determined they were dry rotted so I had to replace them. I used almost 6 feet to do it all. You should have one line come off the back, go through a check-valve, then to a T-fitting, then one line goes to the vacuum ball near the drivers side rear of the engine compartment, one line goes to the cruise (if you have one) and there is another T which goes to the passenger side firewall where it goes inside to your HVAC controls. Check your throttle body for any un-capped lines. I don't recall seeing any on my '91, but you have have some.
My vacuum lines mostly came off the back of the TBI body. However, a quick twist determined they were dry rotted so I had to replace them. I used almost 6 feet to do it all. You should have one line come off the back, go through a check-valve, then to a T-fitting, then one line goes to the vacuum ball near the drivers side rear of the engine compartment, one line goes to the cruise (if you have one) and there is another T which goes to the passenger side firewall where it goes inside to your HVAC controls. Check your throttle body for any un-capped lines. I don't recall seeing any on my '91, but you have have some.
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