[Bigfoot24]

Hi all, thought I’d try my luck. Bought a cherry non-running 01 Taco Limited 3.4 V6 2WD 250k miles for $700. Was told it started dying right after starting, so it might need a fuel pump. Drained all the old gas, put in a new OEM Denso pump, fuel strainer and fuel line filter. Loaner battery (brand new) from my 4Runner. Fired right up! Started and ran about 6 times that day, drove 10 miles just fine. After test drive, shut it off. Now starts but dies after about 2 seconds. No CEL or codes on scanner. It kept running 3 times out of about 30 attempts. It has spark, plugs looks good. I’d love to hear some ideas because this one has me stumped

 

[ShowStop]

Check the fuel pressure regulator and MAF sensor. You might have to look at live OBDII data to see where the issue is at, but definitely sounds air or fuel related.

 

[Bigfoot24]

Thanks for reading! Put in a new Denso (OEM) MAF sensor. No change. Is there a way to check the FRP? Unplugged the vacuum line to the FPR and there’s no gas in it, so I’m assuming the diaphragm inside is intact. Is there a way to check if if the FPR is working? Could it fail and block fuel from making it past?

 

[ShowStop]

Only real way to test is to hook up a fuel pressure gauge which not many people have. Usually when the FPR fails, you have excessive fuel in the vent line. So you are probably good there.

When it runs and dies, this is also a safety trigger for things like a bad crank shaft or cam sensor, knock sensor and other engine management sensors. Any one of those sensors failing could trigger the ECU to shutdown the engine. This is why you probably need to look at live OBDII data and see if you have some issues with data readings. Its really tough to trace if you don't yet have any engine codes pending.

 

[Bigfoot24]

Thanks for the advice! This is driving me INSANE. Hearing new perspectives is extremely helpful! I agree it is like the computer is shutting it down after starting. I was able to capture the live data stream on my scanner when it actually stayed running last night until I shut it off, then wouldn’t stay running again. Here are some images below. Also took off the throttle body and IAC valve unit and cleaned thoroughly. No change. Does any of the data look off?

I also ordered a 1/8” NPT banjo connector to hook up to the fuel rail to plug my fuel pressure tester to downstream of the FPR since these don’t have a schrader test port. I think this is a computer-based issue. I’ve heard of people with similar issue needing a new ECU. Wouldn’t that throw a code though? Also weird that it will stay running once in a blue moon for no apparent reason

 

[ShowStop]

Nothing abnormal in that data, but its only a partial view of data. Missing is data about the other sensors I mentioned which usually requires a technician quality reader. Got any mechanic friends that can run a scan for you?

 

[Bigfoot24]

I see. Unfortunately, I don’t know anyone who would have a higher grade scanner. I agree it would help a lot…I’d rather not start throwing money into the 10+ parts it could be without knowing If you or anyone else have any ideas to what the heck could be going on PLEASE send them my way!

 

[ShowStop]

BTW- Its not unheard of, but pretty rare for the ECU to go bad. The fact that it runs tells you the ECU works. Now you just have to figure out what is causing it to shut off.

 

[Bigfoot24]

That’s good to know, wasn’t sure if ECU problems were common. Just discovered some kind of rodent nest under the intake plenum on top of driver’s side fuel injectors… I’ll clean it out tomorrow and update with anything I find. I’ll take a look at the wiring to the crank position sensor as well. Considering it sometimes stays running, leaning toward a loose or bad connection somewhere

 

[Bigfoot24]

Got it all cleaned out, no wire damage fortunately. Lot of gunk around the crank position sensor and wiring. Cleaned it off. Put everything back together and tried to get it to run, no changes at all.

I noticed one of the coil packs is not Denso (unbranded) and the plug wiring from it is different too. Assuming someone changed 1 but not the other 2 at some point, maybe with some eBay junk. Although it is sparking, I wonder if it’s causing an issue relaying to the computer since it may be sub par quality.

I’ll have a fuel pressure test kit and hardware to hook into the fuel rail this week. Should answer some questions and shed some light on what’s going on. Thanks again everyone for reading! I’ll update with any findings as I keep tinkering

 

[Konno]

Got it all cleaned out, no wire damage fortunately. Lot of gunk around the crank position sensor and wiring. Cleaned it off. Put everything back together and tried to get it to run, no changes at all.


I noticed one of the coil packs is not Denso (unbranded) and the plug wiring from it is different too. Assuming someone changed 1 but not the other 2 at some point, maybe with some eBay junk. Although it is sparking, I wonder if it’s causing an issue relaying to the computer since it may be sub par quality.


I’ll have a fuel pressure test kit and hardware to hook into the fuel rail this week(probably in a few days, going to be a tad busy tommorrow since I'm planning to buy some gear from nearby sports store Outdoor Sports Store | Sporting Goods | Outdoor Gear ). Should answer some questions and shed some light on what’s going on. Thanks again everyone for reading! I’ll update with any findings as I keep tinkering

Doubt 1 coil pack would cause this much malfunction, but test it either way I'd say.

 

[Bigfoot24]

Doubt 1 coil pack would cause this much malfunction, but test it either way I'd say.

Agreed. Tested coil pack resistance - 1.0, 0.7, 0.7 ohms, which, according to the manual is within spec. Put new OEM dual electrodes spark plugs in for the heck of it. Starts WAY quicker and smoother now, but still dies after 2 seconds like the ignition is being switched off.
Got the fuel pressure test kit in today. I’ll update with results

Also, I can’t find the circuit open relay to save my life. My understanding is it keeps the fuel pump on once the truck is running. Please correct me if I’m wrong. Looks like it’s supposed to be a green box fuse under the dash mounted near the steering column. I definitely do not have anything like that anywhere in there. Any ideas where it would be on this 2001 V6?

 

[Bigfoot24]

Hooked up fuel pressure gauge to the driver side fuel rail. Consistently getting 40-42psi immediately after starting. Drops to 26 psi 10 mins later, then 20 psi at 20 mins. Leaky injectors? Could that be the culprit to all of this (start fine then die)? Also noticed a lot of vacuum pressure when opening the gas cap and a gurgling sound inside the tank 10 mins after starting. Tried starting with the gas cap off, no change. Can the evap canister plug up and cause it to die? I am out of ideas why this thing starts up fine then acts like the key is being turned off…

Attached a pic of my fuel rail setup in case anyone wants to do this. Total cost about $45 all off Amazon for gauge kit and hardware. Had to carefully bend the aluminum backing of the belt cover slightly forward to make it fit (doesn’t interfere with pulley).

 

[Bigfoot24]

Decided to order a part number matched ECU replacement off eBay. That will be the last significant part I buy without knowing wtf is going on.. If that doesn’t work I’ll tow it to a shop. Not worth shooting the spendy parts cannon at it hoping it might work

 

[Konno]

Hooked up fuel pressure gauge to the driver side fuel rail. Consistently getting 40-42psi immediately after starting. Drops to 26 psi 10 mins later, then 20 psi at 20 mins. Leaky injectors? Could that be the culprit to all of this (start fine then die)? Also noticed a lot of vacuum pressure when opening the gas cap and a gurgling sound inside the tank 10 mins after starting. Tried starting with the gas cap off, no change. Can the evap canister plug up and cause it to die? I am out of ideas why this thing starts up fine then acts like the key is being turned off…

Pretty confusing, gotta be some sort of leak 'cause pressure drops over time. I'd say take it to the shop, gonna save time probably compared to trying to find w/e is wrong...