1999 4.7 tacoma 4x4 five speed intermittent starting issues

Ooops! its a 2.7 four cylinder not a 4.7. I have no idea where that came from!

Hello, I am a new member living in Alaska. I'm poor and have few mechanical resources but I get by.

It's good to check in with others on challenging puzzles. Here is one I am trying to resolve.

The 25-year-old truck has been reasonably maintained but still has 180K miles under the hood.

...new battery, starter, plugs, wires, filters, fuel pumps, good compression, and so on...

Intermittently, the truck runs over, sounds like it's not getting gas, but it is. It is getting spark. but something is amiss. Leaving the truck for a few hours often finds it starting up the first crank.

I believe the fuel pressure is bleeding off somewhere, but I'm not sure how to test for that.

There are many taco trucks with this issue. I read about it all the time. I have read a definitive answer or troubleshooting method that makes sense.

There is no fuel smell, so I'm not leaking in the fuel line. There is no water in the tank. That is confirmed. Maybe it's a peculiar quirk with a fuel injector. I am not sure how to address that.

The MAF or O2 sensor in bank 1 sometimes throws the P0171 and P0125 codes, but that does not create the starting issue that I'm having. I could replace those items next but neither impacts the initial starting of the vehicle.

I'm ready to entertain ideas. The live data on my code reader has not revealed any obvious clues. I am definitely puzzled.

 

You swap a 2uz?

 

I was wondering the same thing… I could see a typo of 5.7 meaning 2.7 on a desktop keyboard since they are in the same vertical alignment…

 

I would suggest starting with the codes. P0171 is a fuel trim lean code so possibly a vacuum leak or torn intake boot kind of idea. The P0125 is an engine temperature code. Both could potentially cause hard starting on a warm engine. To check the coolant sensor I would unplug it and look at the temp gauge or scan tool live data ideally then short it between it's two terminals if it's a two wire sensor or to ground if it's a single wire. One should make it read all the way negative and the other positive. If that happens replace the sensor. If not you have a wiring issue An alternative way to check is with a cold engine, compare the live data to the air intake temp sensor.

 

This sure sounds like leaky injectors fouling the plugs. They were not mentioned as being changed.

Given enough time they dry off .

In theory the engine should start with a long enough crank time . Not real good on the starter

 

No. my mind was wandering it appears. It's an unmodified 2.7.

 

Not a typo... I had just worked on my son's 4.3 GMC and..well... 2.7...6.7 what's the difference, right? (making fun at my own expense)

 

I appreciate the path. I have been chasing the codes, I just don't want to throw parts at it. I will start your suggested test tonight. Much appreciated.

 

I can see the point. I am going to try to find a vacuum leak before I try that. Do you have a suggestion on how to test the injectors before swapping them? (I already swapped the 2.7 for a 4.7, i jokes)

 

This is very common in the older Honda as the open circuit overheat but it's not as common in Toyota.

I second a leaking or dripping injector during power cycle as mentioned. I know you're in Alaska but it may be worth it to send the 25 y/o injector in for cleaning and flow test. I use MotorWest in CA many times with great result.

 

Hope it leads you to the issue, I hate seeing people blindly fire the parts cannon... it gets expensive quickly and has a high potential to cause other issues.

Without a fuel pressure tester I would try to find a resistance spec (probably in the neighbourhood of 15-25 ohms) and ohm each one and look for the odd one out. I would imagine you get a rich code though from a leaking injector and rough running like my ranger did but I guess you can check.

You may be able to cycle the key a couple times and look down the intake with a camera for droplets on the ends of the injector while it's warm or when you would otherwise experience the hard start

The "textbook" way to check is to connect a fuel pressure gauge, cycle the key to prime the fuel system and note the pressure. Wait a few minutes and see if the pressure decays. If it does then with a fancy scan tool or "injector pulse generator" you would individually command an injector to pulse and note the fuel pressure drop. Cycle the key to prime the fuel system back to top pressure and repeat for every injector and look for the odd one out. Only fire each injector once then start the engine or you may flood it or worse hydrolock it.

Another thing you can look at since you have live data abilities is to watch your fuel trims while the engine is running and note if it's lean more so at idle or higher rpms. Typically a lean at idle condition is more so a vacuum/air leak and lean at high rpm a fueling issue

 

You could try a fuel pressure gauge .

You seem to have no external leaks it would come down to the fuel pump or injectors .

The fuel pump energizes when cranking and running so if it was the pump two or three cranks should start the engine .

There was a very long Saga on here the Best Toyota Techs in the Country ending up using a camera to see the injectors dripping .

Just be careful so many knock off injectors floating around.

Good Luck!

 

does the 4cyl have the coolant temp sensor?
I've had intermittent starting issues all the way up to full blown crank but never start, and replacing the ect cleared it up and it's a cheap part.
or you can also pick up a Bluedriver bluetooth code reader and download the app on your phone. Use it all the time and been a great asset, and cheaper then the huge ones the mechanics use.

 

My 1999 2.7 has a mysterious ‘won’t start when hot” I can drive it to town, shut it off, come back out a store and try it, it turns over but won’t start.. wait 20-30 mins and it will crank right up. I’ve checked the key switch, starter relay, starter, neutral switch… all good. Cold it will crank right up every time.

hope you find your issue

 

I think have found the issue. I am working on it today and will provide an update. During the most recent failure to start, I ran live data on my scanner. I noticed that I was getting intermittent RPM readings. Mostly, there were no RPM readings. SO... I am now replacing the crankshaft AND camshaft position sensors. Additionally, I am verifying that the wires are break-free and have clean connections.

I have read many instances where the engine fault codes do not always catch some position sensor errors. I'll get it done today and provide a report for all who have been following this thread. So far, it is the only time I have had a tangible test to troubleshoot this issue.

The fuel injectors did not change the starting issue. So...here I go. It has been -20 degrees Fahrenheit most of this week, so I had to clear a space in the garage to get this done.

 

I haven’t had any codes on mine…

 

My Chilton's manual says there should be no continuity through the knock sensor. This manual is only for the 89 to '96 models that says the camshaft position sensor should read between the terminals 850 to 1400 ohms in a 5 VZ

 

Okay, It's been too long for an update. The good news is that the replacement of the camshaft and crankshaft potions sensors remedied the starting issue. BUT THERE'S MORE...

The truck starts. That's a win. The first few minutes it runs rough and misfires on cylinder 3. But wait. Only sometimes. Then I get the P0171 fault code. I initially tried to find a vacuum leak. NO luck. I did a visual inspection, then used the carb cleaner to spray to find the leak. No luck.

Here is my OBDII live data:

O2S B1S1 reads between 0.000 v then 0.005 v then 0.015 v then 0.040 v and back to 0.000 v
STFT B1 holds at 0.0% then after ten minutes will go up to 19% and stay

O2s B1 S2 holds at 0.650 v
STFT B1 S2 holds a 99.2%

I think have a bad O2 in bank 1 or a massive vacuum leak. I cant find a leak so...

Any ideas?

 

My dad’s S10 would start , if it would start and run extremely rough, don’t remember what codes he was getting if any. Checked everything we could, coil packs,wires, plugs, crank sensors, o2, vacuum leaks… ended up being a faulty fuel injector, had a small crack near bottom o-ring… replaced it and now truck runs great..

his started acting up one day while running down the interstate it just lost power and acted like it wanted to cut off