Use throttle body cleaner. Not carb cleaner.

 

Whats the difference?

 

Throttle body cleaner is sensor safe. Carb cleaner may or may not be safe.

 

Back on the main subject. I took the morning to test possible suspects of the hot start issue. I tested the sensors outside and it is around -15*C, -10*C. Here are the values I got:

IACV - around 47.5 ohms for both circuits
IAT - 7500 ohms
ECT - 10 700 ohms

I took the fuel temp sensor from my parts truck and from my truck out and put them in water at 43*C and I got a reading around 1300 ohms for both sensors. Is this reading far off enough to cause trouble? This would mean both sensors are bad. If not I'm running out of ideas.

 

Those values are all within spec range... no problems there. This is good news and exactly what you want. Now you KNOW there is something else causing issues. Have you had a chance to check continuity of the circuits (connector plugs and wires) from the sensors all the way back to the ECU plug?

Honestly, the smallest bit of corrosion on a plug / contact could cause a break in a circuit. You are well on your way to solving this problem... almost there!

 

My idle surge problem evolved into a hot start problem haha! Checking continuity will be the next step. But why would continuity be disrupted when the truck is warm? Because when it is started for the first time when cold, it runs awesome until I shut it off, no hesitation on acceleration, and idle sits at 750 RPM.

If I shut the truck off, and I manage to get it running, it will idle at 750 RPM but will drop below 500 RPM when I come to a stop or when I corner.

I believe it is a fuel delivery issue. I checked Rave carefully but it gave me no more info than what I already have. So the next steps are; to check continuity, check fuel pressure at the rail on start up (I think I will install a permanent fuel pressure gauge on the rail, anybody has a suggestion of model and fittings needed?), check for spark, and check the CPS. If anyone has another idea please chime in! I'll post results as soon as I get some.

 

When the ecm is in start mode (ie. you just turned the key to ignition) it goes through a programmed startup sequence. It will check temperatures to determine which fuel map program to use. If the truck is cold a richer mix is needed (sorry for the obvious stuff there) and relies on the ECT for data. When your Fuel temp sensor is hot (around 100*F) at startup the ECM will simply move onto Air flow, O2's, ECT and Crank sensor.

IF the Fuel temp sensor determines the engine is cold when it is NOT you will get a very rich mix in a hot engine. this will throw the o2's out of wack...The ECU thinks it is cold and the O2's will get readings from a hot engine. The system will simply hunt all over the damn place until it finds the right mix at the right rpm for idle for it's current temp. state.

Simple... lol

 

It was what I understood of how the management system works. If I follow your hypothesis, the truck floods itself at startup. I will try to unplug the fuel temp sensor and see what happens. I think it might be possible because I have recurrent O2 codes, P1193 (which I think is not relevant), and another one I can't remember. There has to be a bad communication somewhere which causes the ECM and some sensors. Is the complete ECM startup procedure somewhere in RAVE? It would be super helpful to work my way through.

I think I can rule out the fuel pump as the main cause of the issue. I tried to reprime the fuel lines when it died without any successful result.

 

I wouldn't call it flooding but what you do have is O2's, MAF and ECT constantly working to equalize the rich mix by altering the signals to injectors and IACV...

more of a tug of war than a flood.

 

I'll have a look at the truck this weekend. I'll check for continuity between various sensors and the ECM and try to clean connections and remove some corrosion. Any tip or advice? Should I use dielectric grease on the connections when I put everything back together?

On a side note, is it possible to bench test the sub amplifier? I removed the subs to repair them and since the whole unit is out I'd like to test the amp before putting it back.