Starts fine cold, will not start when hot...already threw a ton at it.

I've read old threads. I've swapped and cleaned 3 MAF/IACs. I've swapped pre and post O2 sensors. I've swapped 3 TPS.

I dropped the truck off at a shop for 3 weeks now. They are giving it back to me.....can't figure it out. Any suggestions here?

1999 3.4 Manual. New JDM transplant when I bought it (new to me under a year). Had several CEL after I drove it home a week. P110, P120 and lots of P420. I think these were the codes. Changes IAC in the intake several times and cleaned it more. Denso part. The TPS, I've tried 2 or 3. Never saw that code again. I had lots of P420. Muffler shop said "Run a ton of Seafoam thru it. Might save you several hundred". This was after then swapped in my two Denso O2 sensors.

Month after this issue started to present itself: Truck starts and drives fine when cold. Once it's hot, it won't start. Or rather, it will start for a second or two and just stumble and not stay lit. I have had success mashing the pedal and holding it down a few times.

When I took it in for body work the shop guy told me the TPS showed 58 ohms and it should show 3?

Took it to a Subaru/Toyota kinda specialist. They kept it three weeks. Said fuel pressure very high. Like 55? And never drops. Said it's way to high holding when off. They swapped in several fuel pumps/pressure regulators??? Said it's within spec with a reman Toyota part from LA, but it didn't fix the issue.

I have no idea what to throw at it now, or even where to start.

Is there an easy way to tell of a leaking injector, or open injectors???

 

What is your coolant temp reading (not the gauge) when the engine is hot?

 

An infrared thermometer on the thermostat will get you very close / in the ballpark.

 

You can rule out EVAP flooding the intake by removing the gas cap after turning off the hot engine.
Put the cap back on right before hot restart.
Wet spark plugs indicates leaking injectors.

 

I wanted to know the coolant temp the PCM is reporting not the actual coolant temp, it should be within a few degrees of actual coolant temp.
If the PCM sees a coolant temp much lower than actual it will give the engine too much fuel and flood it.
Same thing for intake air temperature although it doesn't factor as heavily into fuel calculation as coolant temp.

 

Difficult hot starting is also a sign of tight valve clearances. When did you last check them?

 

Having to hold down the gas pedal while starting with a carbuerated engine is a sure sign of flooding. Never seen this with fuel injected but I suppose its possible. Do you smell fuel when trying to start it? It might be worthwhile just to change the coolant temp sensor, I have never done it with the timing belt cover on but I'm told its possible - have to remove the tube that connects the 2 fuel rails. It's a $50 part.

At least inspect the temp sensor connector and wiring, It actually has a connector on the temp sense and another connector about a foot from that (on my 98 anyhow). Be careful, I broke the tab on the conn but that is one the few wiring harnesses you can replace because its only a foot long if they still make it. If you do separate it spray with electrical contact cleaner.

I knew a guy had a new Chevy and it did this, drove him absolutely nuts and dealer could not help because they could not duplicate it and did not want to drive around with the guy. Finally under threat of lemon law they diagnosed it to a faulty firewall connector.

In your case it sounds like you have spark because it sputters.

 

My bet would be on leaky injectors based on the symptoms.

 

Very much appreciate the assistance, because I am stuck. I will be picking up the truck from the shop by the end of the day. I'll take notes as to what they addressed or checked and move forward from there. In reading old threads I did see that the Coolant Temp Sensor did come up many times in the thread.

I've never checked a valve or tolerances.

 

From my understanding: If the coolant temp sensor is indeed bad what happens is, when your truck is at operating temps the fuel is too hot for how the system is set up to deliver fuel at cold start up. When your truck is at operating temp and you are starting it, the coolant temperature sensor tells the ECM that it needs more fuel for start up, because the smaller amount of fuel that is used for cold start up, gets expanded too quickly by the heat and is not dense enough to start the motor, so the fuel delivery system give you a bit more gas on hot starts. bad sensor=no adjustment to fuel at hot start=no start/rough start.

Sometimes, I have seen people report that the sensor itself was okay, but the wires and harness feeding the temp sensor was too much resistance, so check that possibility too.

It should be fairly easy for your mechanic to test and replace that sensor. Or if you do your own work, get a Factory service manual download of your year model and do the tests and replace if necessary.

Trouble shooting always can take lots of time, but can save you from throwing unnecessary parts at your truck.

Cheers

Edit:if you have to put the throttle pedal down to get a hot start with fuel injection, good chance that your Coolant temperature sensor is on the fritz

also like was said before, you need to test the actual coolant temperature sensor, which is a different sensor than operates your dash board temperature needle. From my understanding, if I am wrong someone please correct me.

 

Are you at very high altitude?

 

UPDATE:

Picked truck up from shop. They stated it's NOT the Coolant Temp Sensor, as they checked/went over that initially. As I stated, they discovered the Fuel Pump was pushing too many PSI and would hold too much after shut off. They replaced with reman Toyota pump and things are in spec, however it did not solve the issue, so I have the truck back....unfixed

Driving it back to my worksite was long enough to get fully hot and operating. When I arrived I turned the truck off. It started back up 30 seconds later with no issue. I left it sit for 1 minute. Same thing. Start up with no issues.

After letting it sit for 5 minutes, the truck would not start.

Sitting for 40 minutes the truck started and I was able to drive it home.

Is this NOT clearly a fuel injector issue, or at least.....isn't that where I should start throwing money? Just pay to have all 6 replaced and make sure to attempt to use Toyota injectors? Beyond my normal skill level I think.

 

Altitude is 2700ft to 3000 daily

 

So I assumed you had spark because I thought it always sputtered but if it's completely dead when cranking you might want to check for spark. If you can remove a spark plug you can do it, search on how it's done although you might have to wear gloves to do it because of the heat and I don't know if its practical in your failure time window. It sounds like a heat soak issue, engine actually gets hotter when shut down because some internal parts are much hotter than the coolant and the heat migrates through the engine. I have had cars where a sensor fails or borderline fails when hot, I'm thinking cam or crank sensor.

But why can't the shop duplicate the issue for you? I know that mechanics don't like intermittent or hard to duplicate issues, I have had those and they told me no thanks but in your case they already started, took your money and need to finish the job. They can actually check for spark w/o removing plug, there is a tester you can insert between plug and wire - you could get one as there only about $10 but should not have to and it still won't tell you what the precise problem is.

 

Your gona have to see what your missing (spark and/or fuel) when it won't start and go from there, it sounds like it's not gona be easy to diagnose over the internet.

 

It's quite possible I get too wordy and I am not articulating things accurately. I am not at all getting schitty, as I am the one needing help. But I don't think this is an ignition issue at all. But maybe it's because my mind is made up that this HAS to be a leaky injector?

To me....it give the classic example of No Start when Hot due to being Flooded.

Again, it will start EVERY day when cold. Run it to work 13 miles for 20 minutes and shut it off. I can restart it immediately. I can wait 1 minute and restart it. Wait 5 minutes and it will not start and seems "flooded". Wait 45 minutes or so and it will start.

Would this not be the case if an injector was leaking or stayed open and was leaking fuel into a cylinder? Would it not most likely pop and fire with minimal fuel (directly after shut off, then restarted), yet if the injector was able to leak into the cylinder for several minutes it would collect too much fuel and flood?

Just asking. I obviously struggled to self diagnose thus far.

The shop's only suggestion was to look into swapping an ECM.

 

If its flooded you should smell un burned gas at exhaust

 

Bad fuel injector(s).

 

hard to say for sure but leaky injectors do seem like a likely culprit. After its hot and you let it sit for a few minutes, enough has leaked out to make it start rough or not at all...until enough time goes by that the leaked fuel evaporates.

beware of buying cheap aftermarket ones or fake OEM ones, they are common online

 

I had this exact problem on a mid-90's 4-cyl Volvo and it was a faulty CPS. (crank position sensor) It was in a high-heat location and the issue was heat-soaking. It was intermitent so it took a long time to diagnose. Classic scenario: Go to the Little League game, car won't start after. Tow it to a shop: next day it starts: NTF. When just by chance I took it to a Volvo specialist someone recommended, he ID'd it fairly quickly. Known issue as it turned out, once you took it to the right place. As a side note it was in a nightmare of a location to access at the back of the engine near the firewall arch. Unless you knew all the tricks, (like this mechanic) as I recall it required dropping the transmission to access it for R&R. Dunno if your specific vehicle has one, but if it does might be worth it to check it out. Good luck.