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Old 08-31-2009, 09:12 PM
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tbi 4.3 issues,

ok we have this 1993 pickup at the shop once again with the same complaints as it origially had months ago of it not having nay power and not able to accelerate hardly at all

i noticed that it just start up then stumbles and dies, yet it will rev up and seem ok, out of gear anyways.

the dying at idle may just be carboned up IAC motor in which is no big deal i will check that tomorrow and clean it. just to eliminate that cuz im sure no one has checked it, probably ever.

now,, i have owned and worked on billions of these tbi chevies and have found that they are extremely temperamental about fuel pressure,

if its too low even by a tiny amount then they just have no power or wont run, or both...

we had a 92 astro van in the shoop here a couple times like this, having the lack of power, as this 93 does,

except for it would idle, but not quite perfectly, or like it should,

even though the spray pattern on the van looked like it was great and spraying gobs of fuel it had no power at all and wouldnt acclerate like this pickup is doing.

we finally just had enough of it and put a new pump in it and bam! it was like brand new strong awesome great and finally done., and has been great ever since.,

well this pickup out here now, we did put a new pump in a couple months back

also new filter and new wires plugs cap rotor and all that.

so it is kind of confusing this time...

also it has a new egr valve in which were problematic commonly on these tbi engines as well.

only thing i can think is faulty new pump

and theres no way to check pressure on these tbi engines they didnt put a test port valve on them for some unknown reason.


what do you think?

maybe something im overlooking or have forgotten to check ?

or bad replacement fuel pump it must be ?(if not a restriction in the pressure line somewhere, or pressure leak inside the tank)


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Old 08-31-2009, 11:41 PM
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When I did my TBI build on my 4.3 I ordered a bung that the fuel line bolts into and it bolts into the Injector pod. I forget what it cost me now but it sure makes checking the fuel pressure easy. You may also want to check the fuel pressure regulator, these are known to go out in time as well on these.
And your right it`s quite common to find the throttle body completely caked with carbon, mine was so bad it took long hours of soaking and a pick tool to get it all out. When the map sensors getting little or no vacuum due to the carbon needless to say it runs lousy.
I went back and located this:
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Old 09-01-2009, 02:08 AM
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even though the spec is 9~ 14 PSI, most TBIs won't run very good if the pressure is at or below about 10 PSI. anything below 9 and they barely move.
but i have seen 1 that ran ok at 6 PSI. it did have a complaint of lack of power, above 70 MPH.

they make an adapter that replaces to fuel filter to check the pressure, i believe Snap-on sells it.

or ATD makes a pretty complete fuel pressure kit.
i have one and so far i haven't ran across a car i haven't been able to hook up to.
it has the adapters needed to hookup to the pressure line at the throttle body.
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Old 09-01-2009, 03:41 AM
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Throw a new filter on it- if the tank is going away or someone sanded the gas on this guy, ...
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Old 09-01-2009, 01:18 PM
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oh well this one and that astro van were MUCH worse, no power to even get going and lucjy to get to 25mph and 70 was way far out of the question haha

so theres an adapter tool so you can check pressure on tbi hmm interesting i need to check that out, need one of them super badly.. like years ago badly..

well dropped the tank real quick since we needed to fix the float arm that fell off the sender anyways and well the new short length of soft hose they give you with the new tbi pumps to connect the pump to the outlet line was split wide open

no wonder..

he should have used a real actual reinforced fuel hose length instead of the garbage they give you with the pump

it great now runs like brand new tons of power like my 91 s10 4.3 has

all it needs now is new intake gaskets it starting to burn water and green color down the front corner of the block driver side.

so we will be doing that soon for the guy im sure,.

i always use a real fuel hose instead of what they give you.

we picked up an 89 cherokee very recently with EFI 4.0 and it was not getting fuel very good either, dying and popping back through the TB unit when trying to rev it up) so we assumed bad fuel pump.
yanked the sender unit out and immediately noticed that the hose they put on the sender unit and pump said specifially "not for fuel use"

it had a hole in it.

so wonder there also..

dumb ppl.. things that happen...

now it also runs like brand new.


Last edited by fast68; 09-01-2009 at 01:29 PM.
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Old 09-01-2009, 04:57 PM
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Good hose at that connection, AND don't use the sh1tty plastic squeeze clamps. Use real screw clamps, or better yet, the band and bolt clamps. I have run into exactly the same problem you have a few times, and this always fixed it. Also, never reuse the pulsator, if it had one. Replace it with a chunk of reinforced fuel injection hose.
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