1st Gen 5VZ-FE Hard Starting

Hello,

I have this issue where if the engine has been sitting for a while I will have difficulty starting. The engine requires I give it some throttle and hold that for a bit until I can release the throttle and then it will properly idle. If I don't give it throttle it will stumble and die immediately. If the engine been run recently it will startup fine.

It then runs rough-ish for a while until the engine warms up.

Using an OBD tool logger I noticed my short term trims are low for about 5 minutes after startup.




Any ideas?

I've tried:
* Cleaned IAC and bench tested
* Cleaned MAF and checked with OBD tool
* Jump started (to see if bad battery was issue)
* Compression test. All cylinders are low (120ish) but I think this may be because I need a new battery.
* Borescope cylinders. Nothing obvious although not sure what I'm looking for.

Thanks for the help.

 

You failed to give us any information about your truck, which makes it more difficult to give you a specific answer. What year? What cab type? What engine? What drivetrain? What trim level? Each variation comes with differences.

Generically, the first thing I'm thinking reading what you've written is you're losing pressure on the fuel line, and when the truck sits, the fuel pump has to re-prime the line to get up to full pressure.

The fuel pump only begins to runs in these trucks (pre-ignition) during cranking. Then (post-ignition), the ECU relies on input (going from memory here) from the crankshaft position sensor to know the truck is running, and keep the fuel pump running.

I could be full of shit with this guess, but if you threw a pressure gauge on the line, you could test the theory. More primitively, if you found a way to prevent spark, then turn the engine over for 3-5 seconds so the fuel pump would fully prime the line, then re-add spark, and crank again to see if it runs smooth it may prove the theory.

I doubt it's the injectors. but if you've swapped injectors at some point, sometimes people have been known to leave behind the O-ring from the original injectors when pulling, leaving a double-O-ring situation which can introduce leaks. Mis-seated injectors/O-rings can also happen if you've had the fuel rail off for some reason in the past, and reinstalled.

It would also be helpful to know if/when/what happened for maintenance in the 6-12 months before this started for you, and whether you have any codes stored or pending.

 

It is a 2001 1st Gen SR5 Access Cab 5VZ-FE, 4WD.

The fuel pump was one of my theories. The pump doesn't turn on when the engine key is at 'on'? I thought the fuel pump started whenever the key was turned to the on position (not just start). I have left the key in the 'on' position prior to starting for several minute under the assumption this would run the fuel pump. There is no impact on startup.

No codes.

 

No, No, and No. Please read. You can, hower, jumper the fuel pump at the relay under the hood to pre-prime the line if you wanted to skip the 'remove spark' suggestion. In fact, I'd suggest trying it.

More info may be gleaned here, along with diagrams.

Here's a link to some diagnostic videos that may help you diagnose starting issues, but note the fuel one is wrong about when the fuel pump turns on, per the fuel circuitry spec in that 1st link, unless they had something changed for the earlier one:
https://www.tundras.com/threads/2005-ac-wont-start-fuel-system-problem.113385/#post-2921783