2000 jimmy hard to start below 35 f.

[ozzig1]

I Have Been Fighting This Problem Since Last Winter. As Long As Its Above 35 It Starts Fine. The Colder It Gets The Harder It Is To Start. If I Turn The Key From Off To Start Several Times It Will Start. Once It Is Started It Will Start Easy The Rest Of The Day. The Check Engine Light Is Not On. Here Is A List Of What Has Been Replaced Or Checked. It Has A 4.3 W Engine------------------------ New Bosch Fuel Pump-------------------------------------------------- New Fuel Pressure Regulator----------------------------------------- Pressure At Pump 84-------------------------------------------------- Pressure After Filter 82---------------------------------------------- Key On Pressure At Valve 61------------------------------------------ Pump Runs While Cranking 61----------------------------------------- New Fuel Pressure Regulator Drops Slowlyto 40 After 5 Min. ----- No Fuel Leaks Found-------------------------------------------------- No Injectors Leaking Under Plenum ---------------------------------- No Bleed Back From Filter To Pump ---------------------------------- New Cap And Rotor---------------------------------------------------- New Water Temp. Sensor---------------------------------------------- New Air Temp. Sensor ------------------------------------------------ I Hope Someone Can Help Me With This Problem. Thanks.

[maxwedge]

Welcome to AF, scan it and see what the coolant temp sensor readings are when cold.

[ozzig1]

I Dont Have A Scanner To Check It. I Had A Shop Check It And They Said It Was Right. I Checked It With A Ohm Meter And It Was Off. So I Put Another New One In.

[old_master]

You have excessive leakdown. When the pump shuts off, fuel pressure must not drop below 55psi for 3 to 5 minutes. The leak could be the check valve in the pump, the fuel lines under the upper intake manifold, or the pressure regulator, also under the upper intake manifold. There is only one way to determine if the problem is under the intake or the pump, and that is to temporarily install a shut off valve to isolate the pump after it builds pressure.

If you checked fuel pump output by restricting the return line and allowed pressure to exceed 75PSI, the fuel pump regulator may be damaged.

[ozzig1]

I Checked The Pressure After The Filter Before The Regulator.i Also Changed The Regulator Twice. No Change. Ive Had The Plenum Off 3 Times. IM GOING TO RECHECK THE BLEED DOWN PRESSURE TIME.

[ozzig1]

Just Rechecked The Leak Down Time. Pressure Was 61 Psi But Wouldnt Hold 55psi For Even 1 Min. Going Get A Valve To See Whats Leaking. Thanks

[old_master]

Clarify something for me... when you checked pump pressure, (82 to 84psi) was that done with the line to the injectors disconnected at the filter outlet? If so, you said there was no leakdown to the pump. That means your leak is under the plenum.

[ozzig1]

I Unhooked The Fuel Filter And Hooked A Gage To The Filter. The Pressure Was 82 Psi.thepressure Held. This Was Done About A Month Ago.the Last Time I Had The Plenum Off I Put In A New Pressure Reg. And Pressurized Everything. No Leaks. I Have Noticed A Gas Odor Outside The Car. Checked For External Leaks. None Found.

[old_master]

Testing pump pressure like that, and holding 82psi, means the check valve in the pump is ok. With no external leaks, the only other place it can leak is under the plenum. Lines, injector, or regulator, that's it.

[ozzig1]

I Just Cant Understand How I Could Have Missed A Leak Under The Plenum.ill Just Have To Take It Off Again For The 4th Time.any Ideas On How To Check For Leaks?

[old_master]

This thread might help you: http://www.automotiveforums.com/vbul...d.php?t=473110

[ozzig1]

That Thread Was For The Older Style Engine. As Soon As I Get Time Im Going To Pull The Plenum Off Again.ill Get Back And Let You Know What I Find. Thanks For All Your Help.

[blazee]

You say that the problem occurs at around 35 f. Are these fuel pressure readings from that temperature or above? The fuel spec is 60-66psi, however during cold conditions the pressure needs to be a little higher than warmer conditions for trouble free starting, so it's preferable to be in the upper range given. That said, most hard starting relating to temperature is usually a combination of fuel pressure and battery voltage. A weak battery or weak fuel pressure is made more apparent during cold weather, because the battery has less power to deliver in colder weather. The battery voltage reduces making a fuel pressure problem more noticeable, or can even cause non/hard starts with a healthy fuel system. When attempting to diagnose a cold weather start problem, it's best to start by making sure that the battery is fully charged, connections are good, and operating correctly. Otherwise, the fuel pressure reading you get may not accurately reflect the condition of the system. There have been several articles written about this occurrence, due to the difficulty many have had identifying it. A customer may have a hard start in the morning (when the temperature is colder) and have the vehicle towed to the shop, and when the tech starts to diagnose the problem later in the day the weather has warmed up and nothing appears to be wrong.

[old_master]

Good point with the electrical aspect, but that will have no effect on pressure leakdown, which was indicated in the first post. The excessive leakdown is a mechanical problem and explains having to cycle the pump several times to build pressure. Spring pressure in the regulator determines the maximum pressure available at the injector and will not rise above that. Excess pressure is returned to the fuel tank. On a system with no leaks, if prime pressure is 61psi, that's the highest the regulator will allow.

[blazee]

I brought up the electrical aspect in response to the issue of it occurring in cold weather. By itself leak down doesn't explain the problem occurring in cold weather. Just like, by itself, the electrical aspect doesn't effect the leak down, however the battery voltage does have a significant effect on fuel pressure which directly effects the leak down.

Cycling the key simply activates the pump additional times and gives the fuel pump more time to build pressure, and could be caused by the leak, low voltage or a multitude of other things. There are many factors that affect fuel pressure other than just the regulator. There is no intelligence built into it. The regulator simply reacts to the fuel pressure that is delivered to it. The pump is designed to operate within a certain range, and the regulator is designed to regulate pressure based on the input being within that range. If the pressure coming into the regulator is out of range, the fuel pressure will change. You can have a system with no leaks, but it may have a weak pump, weak battery, pinched line or clogged fuel filter and the prime pressure could only read 40, 50, or even 60 PSI...... that in no way means that the regulator will not allow more than that.

The leak down still needs to be investigated, I'm simply stating to make sure that the fuel pump is receiving full voltage before starting, because it is a known issue.