I've read here where cycling the key 3 times helps with cold start issues. My 97 TJ has cold start issues lately and the cycling trick usually works. My question is what does the cycling do?
Cold start question
- Thread starter Greasyfingers
- Start date
Cycling the ignition primes the fuel system.
I find that if I just turn the key into the start position and let the fuel pump pressurize (fuel pump hums then stops) before I start it mine starts right up.
The fuel system may be just getting old. I’ve had good luck using Seafoam to clean the fuel injection system. Just follow the directions on the bottle but basically while the engine is warm and idling disconnect the vacuum line going to the brake master cylinder and then just add a small trickle of the seafoam into the vacuum line, a little at a time until the seafoam is gone. The vacuum will suck it through the intake and clean some things up. It takes a little time 20 minutes or so. After youve finished adding the fluid rev the engine to about 2500-3000 rpms and hold it there. The exhaust will smoke A LOT. After the smoke eases off just drive it around. I usually add some to the gas tank too. Helps with mileage and performance a little too.
Most lube shops like jiffy lube offer a service that does the same thing for you if it isn’t something you want to do yourself.
I find that if I just turn the key into the start position and let the fuel pump pressurize (fuel pump hums then stops) before I start it mine starts right up.
The fuel system may be just getting old. I’ve had good luck using Seafoam to clean the fuel injection system. Just follow the directions on the bottle but basically while the engine is warm and idling disconnect the vacuum line going to the brake master cylinder and then just add a small trickle of the seafoam into the vacuum line, a little at a time until the seafoam is gone. The vacuum will suck it through the intake and clean some things up. It takes a little time 20 minutes or so. After youve finished adding the fluid rev the engine to about 2500-3000 rpms and hold it there. The exhaust will smoke A LOT. After the smoke eases off just drive it around. I usually add some to the gas tank too. Helps with mileage and performance a little too.
Most lube shops like jiffy lube offer a service that does the same thing for you if it isn’t something you want to do yourself.
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It sounds like both of you have a failed check valve in the fuel pump assembly. The check valve keeps pressure to the fuel rail when the engine (and the fuel pump) are off. If the check valve fails, it allows the pressure to bleed off, requiring the fuel pump to run for a few seconds to build up the pressure prior to starting.
The reason you need to cycle the key 3 or so times is that the fuel pump only operates for a few seconds if the engine is not running - i.e. when you are trying to start it cold - and that is not enough time to build up sufficient pressure.
If the symptom is that you have to turn the key on and off a few times to get the rig to start after it has been sitting for a while, that is almost always a failed check valve.
The reason you need to cycle the key 3 or so times is that the fuel pump only operates for a few seconds if the engine is not running - i.e. when you are trying to start it cold - and that is not enough time to build up sufficient pressure.
If the symptom is that you have to turn the key on and off a few times to get the rig to start after it has been sitting for a while, that is almost always a failed check valve.
Usually it can mean either the regulator valve or fuel pump check valve is allowing drainback of fuel after shutdown or sometimes a leaky injector failing to shut off.
Looks I need to connect a fuel pressure guage and leave it overnight to see what kind of bleed off I'm getting.
Assuming I need to replace the fuel pump, is there a popular consensus on which brand to get?
Most folks will steer you towards Delphi. I put a brute power in mine source from RockAuto a couple years ago and it's great and 60 bucks.
You also can take apart the fuel pump assembly and just replace components.
-Mac
You also can take apart the fuel pump assembly and just replace components.
-Mac
Pressure bleed off is not really an issue here and does not mean the fuel has completly drained back, ultimately you just want the fuel remain in the line after shutdown. The FSM states that 0 psi is not necessarily an issue. Delphi seems to be one of the better choices for replacement.
My pump packed in a little over six years. I've had a delphi fitted since then with somewhere over 40k miles on it.
I haven't put a gauge on it yet, but there was fuel in the rail this morning. Still had to cycle the key for it to start.
I suspect the fuel rail would retain fuel even if the line drained out since its trapped at a high point and cannot drain back.
It's not really an issue (just an annoyance with the long cold start crank) but I would make sure it is the pump check valve bleeding back down and not a leaky injector washing the cylinder wall down with fuel.
I expect you're right. Fuel came out of the Schrader valve, but wasn't much pressure behind it.
Connect a fuel pressure gauge to the Schrader valve and observe the pressure after turning off the engine. If the pressure drops rapidly after shutdown, it could be a sign of a leaky injector.
When my TJ was doing this I pulled the injector rail, put shop towels under the injectors, then cycled the key. Fuel pressure dropped quickly but the injectors were dry. My problem ended up being the fuel pump check valve.
FWIW, before I dropped the tank I ran some Marvel Mystery Oil through for 2 tanks of fuel hoping it would maybe free up the valve. I'm not a fan of "additives" but it did seem to help. The fuel pressure bled down maybe every 5 cold starts instead of every cold start. It still annoyed me though and wasn't completely fixed so I dropped the tank. Might be worth a shot though.
FWIW, before I dropped the tank I ran some Marvel Mystery Oil through for 2 tanks of fuel hoping it would maybe free up the valve. I'm not a fan of "additives" but it did seem to help. The fuel pressure bled down maybe every 5 cold starts instead of every cold start. It still annoyed me though and wasn't completely fixed so I dropped the tank. Might be worth a shot though.
Agree with the check valve. My 98 kicks right over even when the temps hit single digits.
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