5.7L TBI stalling and low idle help

[Schurkey]

Praying that someone can help me diagnose this issue I'm having. At slow speeds and under load the oil pressure drops to 5ish and stalls out.

You have low oil pressure. This indicates a problem...which might be actual low oil pressure, or it could be a faulty oil pressure sending unit. In this particular case, I think the engine really does have an oil pressure problem.

Educated Guess: Your fuel pump relay, the associated wire harness, or the ECM has failed. The fuel pump is being powered via the oil pressure switch. When the oil pressure goes away...the fuel pump is no longer powered, and the engine dies.

You need to fix the issue with the fuel pump relay, it's harness, or the ECM. Then you need to fix the oil pressure problem.

The ECM is supposed to turn the fuel pump relay on if it gets a signal from the ignition module that the engine is running or cranking. If the ECM isn't getting that signal, it won't turn on the fuel pump relay. It also won't provide any electronic spark advance, so the engine is going to run ****** and have no power and poor fuel economy. It probably has to crank a long time before starting.

Any of this sound familiar?

 

[thinger2]

Its also possible to have intermittant failures at the fuel pump relay and the oil pressure sensor at the same time.
I would expect it to generate a code 54 at some point.
And, FYI if the fuel pump relay is bad they come in two types
the cheapo ones are rated for 15 amps.
NAPA sells one made by Echlin that is rated for 30 amps
Get the 30

 

[Schurkey]

Its also possible to have intermittant failures at the fuel pump relay and the oil pressure sensor at the same time.
I would expect it to generate a code 54 at some point.
And, FYI if the fuel pump relay is bad they come in two types
the cheapo ones are rated for 15 amps.
NAPA sells one made by Echlin that is rated for 30 amps
Get the 30

Constant amperage draw of a fuel pump is about 6--8 amps. I don't know about instantaneous draw, but I bet it's not double the continuous draw, and it'd be for such a short time that I'm not sure it matters.

True enough, I often buy the Echlin line rather than the discount line at NAPA.

 

[thinger2]

Constant amperage draw of a fuel pump is about 6--8 amps. I don't know about instantaneous draw, but I bet it's not double the continuous draw, and it'd be for such a short time that I'm not sure it matters.

True enough, I often buy the Echlin line rather than the discount line at NAPA.

Im not sure that it matters either. Maybe if you are dealing with really long cranking times.
Its more about the Echlin being made in the usa ( at least last time I bought one)
The high amp relay has copper contacts and heavier gauge internals
The quality is much better.
And, it aint from China

 

[James Archer]

Update as of today
- New distributor
- New ignition coil
- New EGR valve
- Pulled the carb apart and new pressure regulator internals
- Timed base 0 with it unplugged then plugged it in.
- pulled the negative terminal for an hour to reset everything
- test TPS voltage. Idle is .74 WOT is 3.4ish
- all new vacuum lines
- pressure tested after fuel filter is 10 psi idle and reving it. On the inlet for the throttle body also tested at 10 psi idle and reving it

So it didn't bogg down after a few mins of driving but now I can hardly give it any gas without it dying out. And it's still struggling at idle. Original cat so I'm thinking it's that possibly?

 

[PlayingWithTBI]

If you can get your fuel pressure up to 13PSI, it would probably help some. 10PSI is a little low, I know GM specs 9 - 13 but you're better off @ the upper end.

 

[retorq]

Update as of today
- New distributor
- New ignition coil
- New EGR valve
- Pulled the carb apart and new pressure regulator internals
- Timed base 0 with it unplugged then plugged it in.
- pulled the negative terminal for an hour to reset everything
- test TPS voltage. Idle is .74 WOT is 3.4ish
- all new vacuum lines
- pressure tested after fuel filter is 10 psi idle and reving it. On the inlet for the throttle body also tested at 10 psi idle and reving it

So it didn't bogg down after a few mins of driving but now I can hardly give it any gas without it dying out. And it's still struggling at idle. Original cat so I'm thinking it's that possibly?

Well at this point you should skip a code reader and just throw a few more parts at it. You'll get it eventually.

 

[thinger2]

Did you at any point check this thing for stored codes?
Stop randomly disconnecting your battery
Every time you do this, you not only loose the code that probably would have cost about 30 bucks to fix, you also loose the stored data that the ecm uses to control the timing air fuel mixture etc..
Every time you disconnect the battery it will run rough u ntill those registers are reset.
Its an OBD1 truck, you don't need a scanner and I see you already have a paperclip.
Read how to retrieve stored OBD1 codes.
Read how long you need to run it in order for codes to set
Check for codes.
The codes tell you which system is malfunctioning.
Knowing which system identifies which components may be causing the problem.
Or, keep buying random parts.

 

[smdk2500]

Did you at any point check this thing for stored codes?
Stop randomly disconnecting your battery
Every time you do this, you not only loose the code that probably would have cost about 30 bucks to fix, you also loose the stored data that the ecm uses to control the timing air fuel mixture etc..
Every time you disconnect the battery it will run rough u ntill those registers are reset.
Its an OBD1 truck, you don't need a scanner and I see you already have a paperclip.
Read how to retrieve stored OBD1 codes.
Read how long you need to run it in order for codes to set
Check for codes.
The codes tell you which system is malfunctioning.
Knowing which system identifies which components may be causing the problem.
Or, keep buying random parts.

Yes but a scanner will tell him how well the other parts are playing with other parts . There could be a possibility that one part is on the verge of becoming bad that could cause another part to act up.

 

[Schurkey]

Did you at any point check this thing for stored codes?...
...Its an OBD1 truck, you don't need a scanner and I see you already have a paperclip...
...Or, keep buying random parts.

^^^ I agree with most of that.

Don't underestimate a real scan tool. Live data is often as helpful--or more--than "codes".

But, yes, any form of diagnosis beats shot-gunning "new" parts.