Long crank, no faults

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Jimmy Brooks

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Checked mine again after sitting one day and got same results as last time - ignition on, before cranking, showed 650 kpa (95 psi). I’ll see if I can get a graph of the pressure increase on cranking. Maybe comparing graphs can give you some idea of the hpfp performance.

Also wondering if you can see the temp sensor voltages when the car is cold. Just thinking that a bad temp sensor might be telling the engine that it’s warmer than it actually is, giving the wrong air/fuel mixture. You might try to rule that out - and maybe change the fuel rail pressure sensor - before resorting to changing any fuel pumps. I remember someone saying the fuel rail pressure sensor is not too difficult to change out, but haven‘t done it myself. I think it’s at the firewall end of the passenger side fuel rail - not sure if you can reach from topside, or maybe go through passenger wheel well?
Which temp sensors should I check. I checked the fuel rail pressure voltages before all this and they looked good and changed voltage when engine rpm is climbing.
 

f1racer328

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If you floor the accelerator pedal while starting, you can crank the car as long as you desire.

I’m not 100% sure, but I’m pretty sure it cuts fuel.

This might help isolate your problem. Maybe monitor the low pressure and high pressure pumps while doing this, and see if it starts normally after, or not.
 

Jimmy Brooks

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Car has been in an insulated garage for the last 2 days and it’s cold started perfectly normal 3 times in the garage. Think it’s gotta be a temperature thing. Which temp sensors in the engine should I check that would affect a cold start.
 

jlglr4

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There are two temp sensors, one just below the T-stat in one of the radiator hoses near the water pump, and the other mounted in the rear crossover. I don’t know which would be causing the trouble. I think the rear registers the hot side of the coolant system leaving the block, and the front registers the cold side leaving the radiator. So, I’d be inclined to think it’s the rear sensor used for fuel control, but not entirely sure - could use both. I think the car does do a logic check of some kind by comparing the two values to see if the hot/cold differential is within some kind of range. You might try to first see the readings on both when the engine is cold and see if one looks off - I think they are just called temp sensor 1 and 2 in the gap tool.
 

Jimmy Brooks

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@jlglr4

On temp sensors 1 I’m getting a reading of only .6 volts while on the other sensor I’m getting 2.4 volts. Is the temp 1 sensor a 5V sensor? Because normally the 5V sensors are supposed to sit between .8-4V. Just thought it was weird that it wouldn’t throw a code for low voltage on that sensor
 
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jlglr4

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Yeah, I think there is something wrong with that 0.6 v. I just went out and measured mine (dead cold). I’m seeing close numbers on both.
FB50FCA7-D843-4ED1-A45A-1329940FC964.png
 

jlglr4

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I can’t remember if you have the v8 or v6. If you have the v8, you might get to it. If you have the v6, it’s harder to get to with the supercharger sticking up. Not sure if you can reach it. Maybe remove the windshield cowling? Not sure if that would give you better access.
 

Jimmy Brooks

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I can’t remember if you have the v8 or v6. If you have the v8, you might get to it. If you have the v6, it’s harder to get to with the supercharger sticking up. Not sure if you can reach it. Maybe remove the windshield cowling? Not sure if that would give you better access.

Realized that I didn’t look at the voltage when the car was cold, checked it again right after I started the car and this is what my voltage read. However after driving for about 5-7 mins the voltage went back down to .6ish. Would this mean I still have a bad sensor?
 

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jlglr4

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As the coolant heats up, temp sensor 1 will trend towards 0.5 volts. Temp sensor 2 will stay cooler (higher volts) because that‘s the cold side coming out of the radiator. So the general trend looks okay. Right after starting, you’re already putting some heat into the system, which might explain why sensor 1 is lower than sensor 2. I’d check them dead cold before starting just to make sure they’re about the same, since that’s when you are having an issue. If they are about the same, I think you can rule out the temp sensors.
 

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