Troubleshooting Help- 2.7L GEN 1 Taco Crank and Stall

Hello all,

I hope that it’s ok to post this here, I also posted to the 1st gen Tacoma thread and haven’t been receiving any input so I figured I’d try here too.

My truck is a 2000 Tacoma Prerunner 4x4 with the 3RZ 2.7L engine.

Fall of 2022 I started to get a CEL as well as a rough start and idle as well as terrible fuel mileage. I was pretty sure at this time that the truck had a pretty bad exhaust leak as well. Reading the CEL produced a P0300, P0301, and P0303.

Work completed: I replaced the plugs and wires with NGK platinum, and the coils with Hitachi because I could not find OEM Denso. MAF Cleaned with no noticeable difference.

The CEL remained even after clearing the codes, the truck still had misfires, a rough idle and poor fuel economy.

Work Completed: In the spring and summer of 2023 I decided to replace the injectors and upgrade the exhaust and intake. I installed LCE Engineering straight tube headers, Magnaflow hi-flow cat and full 2.5" bolt on LCE exhaust with all new gaskets and a K&N intake. I mistakenly ordered Aisin pink top injectors thinking that they were correct for my engine and upon install I realized that they were a few millimeters too tall. I did not have time to wait to get my OEM injectors remanufactured so I completed the install with the pink tops. The fuel rail would not fully seat on the cylinder head but I torqued the fuel rail down as evenly as possible andmonitored for leaks. I also thoroughly cleaned the throttle body while it was removed from the engine.

The truck ran rich and the fuel mileage became even worse and the CEL remained. The misfires were not as noticeable but the truck would sporadically run very rough and stall at stop signs after 30+ minutes of driving.

Work completed: I replaced the wires (with heavy gauge race type wires from LCE), coils and plugs (OEM copper replacement) and ended up going back to a second set of new NGK wires and NGK platinum plugs.

Fall of 2024: The aforementioned issues still existed and a new fault appeared. After driving to work in the morning and parking the truck for most of the day, the truck would not start for 2-5 minutes. It would crank and not fire, cycling the ignition multiple times and fluttering theaccelerator pedal would eventually get the truck to fire with a very rough start. All of these symptoms combined with similar information that I've gathered from posts on this forum led me to believe that the fuel pump may be failing or the filter was clogged as well as not having theappropriate injectors.

Winter of 2024-25 all of the same issues and faults were still occurring so I decided to replace the injectors again with OEM. Through days of searching the internet I could not come up with a new set of OEM Denso (Short, fat, brown connector style) injectors, so I ordered areplacement set from TRQ. I installed thoseinjectors and attempted to start the truck. After a few tries the truck would fire and die after a few seconds. Cycling the key to the off position and retrying would have the same results.Attempting to start after a stall with the key in the ON position would mostly result in long crank and weak-sputtering ignition and stall. At this point I was getting very frustrated and went full parts cannon on it.

Work completed: OEM replacement (NAPA) IAC Valve installed- Same results. MAF cleanedagain- Same results. OEM replacement (O'Reilly's) fuel filter installed- Initially leaked at return line, tightened and same result. Swap back to OEM brown top injectors- Same result. New Denso fuel pump and Delphi strainer installed- Fuel pump priming is now much more audible but same result. Swap back to TRQ replacement injectors- Same result. Fuel injection relay replaced and all fuses checked- Same result. I have checked the OBD2 codes and nothing is populating now, the codes were cleared due to many nights of negative battery lead being disconnected and I don't think the engine is running long enough to populate any new codes.

Update to work completed: Crankshaft and Camshaft position sensor replaced with Denso OEM. Issue not resolved. Following the FSM troubleshooting tree for no crank (immediate stall), I checked the fuel pump operation by grounding pin (I think FC) to body ground, fuel pump works and there is pressure in the return hose. Then I checked the starter signal circuit and it was in spec. I checked the ECM power source circuit and it was in spec. Then I started checking the circuit opening relay and it seemed to be within spec except for one of the unpowered continuity checks. The FSM says to check for continuity between pin 3-5 and that was fine, the next check I think is between pin 1-2 and there should be continuity, my relay was ohming out around 127ohms. It does have continuity but it seems high.

The next step is as follows:
Check for open in harness and connector
between EFI main relay and circuit opening
relay, circuit opening relay and ECM. I very possibly may be reading this or the wiring diagram wrong but I don’t think that the EFI relay and the C/O relay share the same circuit at any point besides the ECM. With that being said, I rang out every wire from the EFI relay to its connectors all the way to the ECM and did the same for the C/O relay to its connectors under the drivers seat as well as to the fuel pump connector and the ECM, all wires rang out and had good continuity. The last step of this troubleshooting tree is replace the ECM and that reality is killing me because I cannot find a reputable replacement (only flagship one has my part number and not sure if they are good or not, internet says no).

I have read so many posts on these forums about the misfires, rough idle and now the crank and die issue and have done many of the same repairs that others have to solve this issue but it still persists.

Currently I am waiting for fuel injector cups, injector gaskets to replace the original "injector insulator (lower gasket)", vacuum hoses, fuel pressure regulator, both oxygen sensors, and OEM circuit opening relay to arrive to see if any of those parts will fix the issue but I am not hopeful. I feel like the misfires, random stalls, random hard starts and finally crank and die issues are all related and probably due to some ridiculous, small short somewhere in the engine control system wiring or a faulty ECM (I really hope its not that). I have also purchased a power probe, power probe open circuit finder, smoke machine for vacuum leak checks, compression tester, fuel pressure tester, and other tools to help in diagnosing the issue if it turns out to be a wiring issue.

If anyone has any suggestion on where to go from here I am open to suggestions.

Thanks,

Cody

 

Welcome! I'd wager you'll get more responses on your first gen section post, but no harm in introducing yourself and explaining here too I'm my opinion. Hope someone is along to help.