3.4 T100 dies on highway, now crank no start

Cruising in 5th in my 1997 T100 3.4 5 speed, and suddenly have no engine power. Soon as I pushed the clutch in it died, so I pulled over. On the side of the road it would crank no start, maybe a slight stumble. I cleaned the MAF, got a buddy to bring me a crank position sensor because I thought maybe that was the issue but it didn’t help. Pulled the fuel like off after the filter and it had lots of flow when cranking. Pulled a plug and it wasn’t wet but pretty black with carbon. After a couple hours it’s started to stumble a little bit more now but unpredictablbly dies with throttle. No codes or cel this whole time.

Got the truck trailered home and have been working on it since. Swapped maf with a buddies truck, made no difference. All plugs have strong spark (although seems to only be once the engine starts to stumble on the other cylinders ?) but are pretty black with carbon but not wet. Cracked a banjo bolt on the fuel rail and lots of gas came out when cranking. No fuel coming out of the return line from fuel pressure regulator, whereas my friends truck had lots coming out. Made me thing fuel pump wasn’t pushing enough pressure, so I put a new pump in and for a couple minutes I thought it was running normally. Then shut it off, and when i started it next, was only stumbling again. Any ideas ? i’m lost

 

A plugged fuel filter would let some gas go through but not enough on demand.

Fuel issues = fuel pump, fuel filter, fuel pressure regulator,

Fuel pump doesn't start until truck is turningover I believe,

you need 42 pounds of fuel pressure

 

@Dm93 might have some ideas.

Key notes:

1. Good Spark
2. New fuel pump
3. No fuel from return line (HINT)
4. We do not know actual fuel pressure (PSI)
5. Not 100% on wiring ability to carry sufficient current (Fuel pressure test would help)
6. Plugs appear dry when checked. (HINT)
7. We haven't tried spraying any fuel into the intake when cranking to see if we have a true (fuel issue) - (Try this)
8. CKP Sensor new (unknow make) Likely never was an issue.
9. No mention of a scan tool. Do we have a scan tool? Any codes? Is the CEL on?

OP, if you can help out by answering / trying the notes above, we might be able to help more.

 

I bypassed the filter to check if it was the issue but didn’t make a difference. I am thinking regulator, but if the regulator was bad wouldn’t it be letting too much fuel bypass?. Or I might have a blockage in a line between filter and the motor but not sure how to check that or if i can blow an air nozzle down the line to try and clear it out

 

I’m going to go get a can of starting fluid and try that right now, will report back shortly.

Only a cheap code scanner, showing no codes and no cel on dash when running (light does illuminate in on position).

Fuel pump is a lordco Spectra as it’s all the had, but CKP sensor was a Denso. Yes likely a want the issue.

Sadly my local parts stores don’t rent fuel pressure testers so I can’t get an accurate psi.

 

Who’s to say it isn’t stuck closed, blocking off the by-pass to the return line.
You say the return line has little to no fuel coming out of it.
At idle, you should have a lot of fuel going through the regulator by-pass to the return line.

 

BTW, I'm not saying it is the regulator.
I'm still at checking for fuel (spay intake) and PSI readings if needed.

 

Okay, now this is SUPER weird. Sprayed starting fluid into the air filter for 2-3 seconds. Started up seemed to be idling right, started to just barely stumble and i have it 2 or three more snorts of starting fluid to the air filter and now it’s running perfect. Like perfect idle, throttle response, everything. Where as just seconds ago before trying starting fluid i fired it up, it was at 1000 rpm for a second then stumbled and died.

 

What happens when you turn the engine off.
Then let it sit a few mins?

The engine makes more vacuum and reads more air flow with the engine running.
The only things you did were move the intake tube (maf attached) and got the engine turning faster.

Make sure that MAF sensor is plugged in really good.
And see what happens?

 

MAF is plugged in really well. Took it for a drive and after only having gave it some starting fluid on the air filter 5 or so minutes ago, its running way better actually revs up, but bucks when moving under power.
Shut it off going to let it sit for a bit and see what happens.

Thank you for the quick help so far

 

After it running better with some starter fluid on the air filter, took it for a spin around the block and it was bucking under load while moving. Shut it off for a few minutes and now it’s back to starting around 1000rpm then just stumbling and dying out.

Seems like this must be a fuel issue since starting fluid in the air cleaner makes it run better

 

So did you replace the fuel filter or not?

 

I didn’t because my local lordco didn’t have one, but I bypassed it and it didn’t make any difference. Obviously put it back in after a short try with it bypassed

 

Hopefully…….

 

He said he by-passed the filter and the issue remained.
So he put the filter back on.

We need a PSI on fuel pressure when this happens.
Be nice to see STFT as this happens too.