Tbi fuel pressure

[Scooterwrench]

Common practice is to turn the key on and listen for the fuel pump to shut off then immediately crank for 2sec,relese the key from the start position and listen for the pump to shut off again then immediately crank again. Normally they will bust right off on the second crank.
I've noticed that my truck has not been lighting off on the second crank recently and have had to hit it a third time. I've heard they sell a winter blend of this already crappy fuel they're charging us so much for that may be causing the hard starting issues or our old TBI systems don't like cold weather either.

 

[evilunclegrimace]

Did you ever verify what the fuel pressure is?

 

[GoToGuy]

Fuel pump pressure is higher than the diaphragm regulated 9-13 psi book value. Bleed down is not specified , except that OE diaphram has small bleed down hole to relieve pump pressure on shutdown. Every time key is switched to on position ECM activates fuel for 2 seconds to prime injectors for shorter cranking faster start. If there is a break in the priming circuit, long cranking results, as the fuel pump is waiting for oil pressure to build and close the low oil pressure switch for pump power circuit.

 

[Road Trip]

There isn't a check valve in a TBI setup. The flat diaphragm (I don't have a picture of it) returns whatever it needs in order to maintain pressure while the pump is running. Once you shut off the pump, your pressure will drop immediately.

Well stated, PlayingWithTBI.

I just scanned the '89 Service Manual, and found the following at the bottom of p. 1179:

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[VIKING_MECHANIC]

The fuel pressure is 9psi, although that's with KOEO, I haven't checked with it running yet. IIRC, I've had this labored cranking since the summer when I put the engine in the truck, although it was less pronounced. I'm pretty sure it's because the timming which I need to re-evaluate here soon. Although weirdly enough, once its running and after about 5 minutes and I shut it off, it will immediately start back up(after sitting for a minute or two).

I'm just trying to figure out these two issues I'm having with the truck before I do my carb swap in a few months.

The labored crank(mainly when the engine has been sitting for a while), which I'm almost positive is timing related.

The other issue is it will randomly die after idling for about 20 minutes or if I take it on a short drive. I have looked at live data, and everything looks normal from what I understand.

I'm just want to make sure the fuel pump is working properly and not really sure how to test that(other than psi). I'm just wondering if the pump is getting hot by building internal resistance and is shutting down, as there's nothing in the data that is pointing to why the engine dies.

I just want eliminate any issues that aren't related to the ecm(like sensors etc). before I do my carb swap.

 

[evilunclegrimace]

Dead head the pump and see what kind of pressure it builds.

 

[VIKING_MECHANIC]

Dead head the pump and see what kind of pressure it builds.

How do I do that?

 

[Schurkey]

I've heard they sell a winter blend of this already crappy fuel they're charging us so much for that may be causing the hard starting issues or our old TBI systems don't like cold weather either.

Winter-blend fuel has been used for decades. Winter-blend fuel is cheaper than summer-blend. If you don't like the cost of fuel now, you're gonna really hate it when they switch back to summer-blend later this year.

Winter-blend fuel makes for EASIER starting in the winter. You'd have real problems with summer-blend fuel in January...depending on where you live.

TBI systems have no inherent problems down to -20F assuming everything is in good condition. Below -20F, they may or may not have issues depending on engine condition, how old the fuel is, how thick the oil is, how strong the battery is, and numerous other variables. In other words, if it's warmer than -20F, and your TBI doesn't start...something is wrong.

 

[evilunclegrimace]

How do I do that?

Temporarily pinch of the return line with a pair of hose pliers to see how much pressure the pump makes.

 

[Scooterwrench]

Winter-blend fuel has been used for decades. Winter-blend fuel is cheaper than summer-blend. If you don't like the cost of fuel now, you're gonna really hate it when they switch back to summer-blend later this year.

Winter-blend fuel makes for EASIER starting in the winter. You'd have real problems with summer-blend fuel in January...depending on where you live.

TBI systems have no inherent problems down to -20F assuming everything is in good condition. Below -20F, they may or may not have issues depending on engine condition, how old the fuel is, how thick the oil is, how strong the battery is, and numerous other variables. In other words, if it's warmer than -20F, and your TBI doesn't start...something is wrong.

Mine is 100% New pump,new fuel filter,TB rebuilt with adjustable regulator set at 10-1/2lbs. Battery is new and it spins it well. ECT in spec. There is no other reason for it to not bust right off other than the cold temps and/or something with the fuel. Once it lights off it runs good.