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Tbi, map sensors, and headaches

Alex guadalupe

Alex guadalupe

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The stories follows me, 24 years old stuck in fort irwin with an 87 k5blazer
350 TBI
To get to the point, I had a wicked loss of power
Hesitation
Then backfire through the tbi
Took the truck to a friend on post amd we found out that the injectors were pissing fuel.
3 days later I rebuilt the tbi with new injectors and gaskets
After that my truck would idle rough
Then just die
We found that my map sensor took a shit
Another week goes by and with help I have a new map sensor
But now she wont even stay on with that new map sensor connected
She dies and when I got to start it back up I get nothing but cranking and the starter whinning that its turning forever

I get spark and fuel deliver
Ive tride everything I know but I just dont have enough experience with TBI
Can anyone help me please
 
When a vehicle backfires it is a sign of timing issues...either valve train or ignition. When a vehicle backfires through the intake manifold it is a sign of timing being too advanced. The backfire through the TBI could be what caused the blown out the injector seals, and not what caused the backfire to begin with. Make sure the distributor is not loose and spinning around all over the place.
 
Alex guadalupe said:
Would that timing issue show itself at idle
With the map sensor disconnected
And what would cause the engine to not want to start with the map sensor hooked up?????
Click to expand...
Timing

You do know to unhook the disconnect at the firewall and set the timing at 0?
 
This will be my first time having any kind of timing issue
In short
No I dont know
I just got back from a quick ride where I installed my old map sensor back and the idle issue got a little better
But im getting hesitation and loss of power at part throttle
Are you guys saying that these issues could be timing related
And if so how would I be able to diagnose if it is a timing issue
Ive taken a timing light to it before and at idle it was fine
But could the problem be happen after I give it a little throttle???

Im sorry if I'm asking so many questions
This will be my first tbi and if from what you guys are saying
It could also ne my first timing issue
 
There's a disconnect on the firewall that is integral with the timing circuit.

Shut the truck off. Unhook it, restart the truck. Set the timing at 0.
Turn truck off, then reconnect it.

Not sure what color yours is. But if you are missing the wiring diagram (with wire colors ;) ) then go to the "injection section" and they are posted at the top.

Start there, then we will go from there.
 
If the timing was off, I'd hook everything back up and drive it.

If the timing was at 0, we need to keep digging
 
Pissing fuel out of the injectors is usually a tell tale sign of coolant temp sender being bad. I would suggest getting an aldl cable and reading all the sensor data. You can do this using winaldl or tunerprort for free once you have the cable.

Usually the temp sensor fails to -45 degrees or so and adds a ton of fuel to compensate.
 
I replaced the temp sensor and was still pissing fuel
Once I replaced the injectors I started getting my awkward behavior with the map sensor
Once I tried replacing that I couldn't even turn my truck back on
And if you read in my earlier replies
I had installed my old map sensor and went back to square one
Engine idling funny
Loss of power at part throttle
And afterfire through the exhaust
From what I'm getting in this thread
It could be a timing issue
Im just trying to get it all figured out
 
Did you zero out the tps after the tbi rebuild?

You are just guessing until you put a scanner on it to read all sensors.

Some of the issue you discribe can be caused by a faulty icm
 
I didnt I had to zero out the tps
I only removed the top part of the tbi that holds the injectors
And my icm is new
Very new
I went ahead and put the old map sensor on and went back to square one to find I may have timing issues
Semi decent idle but when I give her partial throttle she backfires hard through the exhaust
Leaving behind black smoke
All after a decent loss of power
 
Did you put your hand on the distributor and try to turn it, in order to see if the distributor hold down clamp is loose? With your truck backfiring first out the intake manifold and now out of the exhaust manifolds, it sounds like the distributor is loose and spinning all over the place as the engine runs.
 
Alex guadalupe said:
I have not tried to turn the distributor yet
I am looking up how it would effect timing under load
Click to expand...

If the distributor was loose enough an engine load would spin it around like a top. It would be 45 degrees advanced one minute, and 38 degrees retarded the next. :D
 
1-ton

Thats insane amountd of advance and retard
I'm going to check it out
A buddy of mine has a timing light that ill be using to make sure my shit is right
I just dont have a tacomitter in my truck
Wich I'm assuming won't be an issue
 
Alex guadalupe said:
I just dont have a tacomitter in my truck
Wich I'm assuming won't be an issue
Click to expand...

Tachometer doesn't tell you engine timing...

Throw my vote on having a timing issue. You may or may not have other issues, but backfiring is not a fuel delivery/pressure issue.

1-ton said:
The backfire through the TBI could be what caused the blown out the injector seals, and not what caused the backfire to begin with.
Click to expand...

This.
 
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