I have normal cold starts, warmups and running with normal temps, park for longer that 3 minutes the restarts run like on 4 cylinders stumbling around like too rich but no black smoke. Rev to 2,500 for 20 seconds it then clears up running on all 8 again with a normal idle.
If it sits from nornal running for 45 minutes or longer it will restart and run as normal. Seems worse parking after a highway run vs 25 mph town driving, acts up more times after the highway restarts.
Basically it's acting like a carbed engine with vapor-lock problems.
Oversize custom radiator, new stat temps dead solid be it running in 50*F or over 95*F it's not a cooling issue.
Temp gauge functions full scale cold to max hot by grounding the lead to the gauge sensor checking the gauge sweep, reads slightly below half scale.
I'm thinking the sensor at the base of the stat housing as well the fuel rail temp sensor, i'm not one that throws parts and money at a problem like the dealership mentioned "change all the sensors to be safe" idea.
Yeah right.
Any tips or clues on this hot restart problem?
Thanks, Carl

 

1. Custom rad - pix and more details, PLEASE. So many members are faced with new rad for a D1 and they are pricey.

2. Vapor locked - points toward the engine fuel temp sensor, located on the driver side fuel rail.

3. Might also be the coolant temp sensor. This is not the gauge sender, which you have discovered is not very accurate, it is the one next door that has a square plastic connector on top with two wires. The ECU reads it to determine coolant temp and will fatten pulse width of signals to injectors to send for fuel. Don't know if you have a bad one, or a wiring issue. On my scanner, the coolant temp makes sense normally (it is ambient when vehicle has been parked over night, rising to thermostat temp as vehicle warms up); but if I unplug the sender connector it reads -40F on the scanner. So if you have a scanner, you can observe the coolant temp in digital fashion when the mayhem is happening.

5. Pix of D1 intake with coolant sensor on right. Also, for a cheap test, when this happens, spray the fuel rail temp sensor with brake parts cleaner or cold water and see if that makes things return to normal quickly.

For a D1 from the RAVE:


specification vehicles.

AND

Engine coolant temperature sensor (ECT Sensor)
This sensor consists of a temperature dependant
resistive metal strip. The resistance of the strip varies
considerably with coolant temperature, i.e. from 28K

ohms at - 30

°C to 90 ohms at 130°C, and 300 Ohms

at 85°C. The ECT Sensor signal is vital to engine
running, as the correct fuelling is dependant upon
engine temperature i.e. richer mixture at low

temperatures. If the sensor is disconnected or failure

occurs a default value will be supplied to the system.
The initial default value selected will be based on the
value of the air intake temperature. This will increase
to a nominal warmed up value over an individual time,
programmed for each default value. The fault may not
be evident to the driver, there may be a hot restart
problem. The fault is indicated by illumination of the
malfunction indicator light (MIL) on North American

specification vehicles.

 

Savannah Buzz, you can get a stock D1 radiator recored at a shop with more rows; like 5 instead of 4. It has to be a shop that knows what they're doing though. I had mine recored a little over a year ago. It tan me about $370 but I live in the "Chicago area" so everything is more expensive. If I wasn't in a time crunch when I had it done I would have increased the rows.

 

If you don't have a CEL - (MIL) this might be the cause;

Fuel pressure regulator
The fuel pressure regulator is located at the rear of
the engine in the fuel rail. It consists of a fuel inlet,
outlet, vacuum port and internal diaphragm.
When the engine is under high manifold depression,
the applied vacuum sucks the diaphragm of its seat,
allowing fuel to return to the tank, resulting in a lower
fuel pressure. This is necessary because the high
depression will try to suck the fuel from the injector,
resulting in overfuelling if the pressure remained
constant. Failure will result in a rich mixture at idle but
normal at full load, or a rich mixture resulting in engine
flooding, or a weak mixture. Although the fault will not
illuminate the MIL, faults caused by the failure may be
indicated.

Check vacuum hose to FPR diaphragm. You can check the FPR diaphragm with a vacuum pump to see if it holds or looses pressure. You can pinch off (or remove) the vacuum hose while it's running to see how engine runs then.

Just another area to check besides the fuel temp sensor and ECU coolant temp sensor. I personally hope it isn't the FPR....they are expensive!

 

You can also access the schrader valve on the passenger fuel rail to watch pressure. 32 - 34 PSI

IMHO the diagnosis will probably not be the coolant sensor, because if it goes crazy, then resets as truck cools off, the coolant sensor does not cool off as quick as the FPR or the fuel temp sensor ( they are outside the block).

$370 beats $600 for a new rad.

 

Fuel economy with a bad coolant temp sensor is horrendous.....I experienced 230mpt to 320mpt after replacement.

Hey BierNut, you using a dizzy with this motor?

 

I apologize for not looking at the year, you might not have an OBDII port to read digital data. If that is the case, you may be able to cool down the coolant temp sensor, but on mine the business end pokes all the way into the coolant. Sometimes they get covered with calcium buildup, you can remove and scrub with a brush. They also are just a variable resistor, so you can read them with a meter and look for the value changing.

 

You got that right! The radiator guy looked up the price new to see if it was worth it. He just about had a heart attack when he saw what a genuine new one was fetching, LOL.