94 Explorer - I have an intermittent no start problem. Sometimes it fires right up perfectly fine, other time it will crank and crank and not start. It always eventually starts after the 4th or 5th time. After it finally starts it runs fine. No check engine light. I just changed spark plugs and fuel filter (needed to be done anyway) and there's no change. Also tried changing fuel pump relay. Fuel pressure is a steady 30 psi when running, goes up to about 35 psi when turned off, and will hold pressure fine for 5+ minutes (that was tested when it decided not to act up, though...) Any ideas?
Intermittent no start
- Thread starter exranger06
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Next time it acts up give it a shot of starting fluid. It it fires you have fuel system problems, if not its probably ignition or a power supply problem.
Sensors, ignition control modules all can have intermittent problems as can the ignition switch itself.
Check the ignition switch first when it acts up. It controls power to the ignition and the fuel and can fool you into thinking other parts are defective.
Your fuel pressure is at the lower end of the spec but should still be satisfactory to run the engine.
KOEO 35-45 psi
Running 30-40 psi
Sensors, ignition control modules all can have intermittent problems as can the ignition switch itself.
Check the ignition switch first when it acts up. It controls power to the ignition and the fuel and can fool you into thinking other parts are defective.
Your fuel pressure is at the lower end of the spec but should still be satisfactory to run the engine.
KOEO 35-45 psi
Running 30-40 psi
Battery grounds
The worst part about this is, my mother is the only one who ever drives this car. And the only time it doesn't start is when she is out runnning errands while I'm at work 20 miles away. I found a video online with a Ranger with the same problem and it had a bad ground on the fuel pump relay. I'm gonna look into that tonight. If not, I'll have to try and borrow the car for the next few days so I can diagnose it when it starts acting up.
Does the ck eng light come on when the key is in the "On/RUN" position with engine stopped? Does the light go out when the engine is cranking over? Does it act up more when cold or warm?
Concerning fuel problems, I left fuel pressure gauges taped to the windshield for days sometimes trying to catch fuel pump problems. Also, even though there is not a ck eng light, pull codes and look for a code referencing "fuel pump primary". If the fuel pump relay is commanded on, but for whatever reason doesn't supply power to the pump it will set this code. Sometimes the relay (which you replaced), sometimes a bad contact in the relay block or harness. Tap the emergency fuel cut switch a few times to trip it, then press in the button on the top to reset it to eliminate that as a cause.
As posted above, always a good idea to check the grounds under the hood and sometimes under the dash or kick panels. Those things cause intermittents that can make a tech pull his hair out.
Concerning fuel problems, I left fuel pressure gauges taped to the windshield for days sometimes trying to catch fuel pump problems. Also, even though there is not a ck eng light, pull codes and look for a code referencing "fuel pump primary". If the fuel pump relay is commanded on, but for whatever reason doesn't supply power to the pump it will set this code. Sometimes the relay (which you replaced), sometimes a bad contact in the relay block or harness. Tap the emergency fuel cut switch a few times to trip it, then press in the button on the top to reset it to eliminate that as a cause.
As posted above, always a good idea to check the grounds under the hood and sometimes under the dash or kick panels. Those things cause intermittents that can make a tech pull his hair out.
OP update: Man, this thing is difficult to diagnose. I basically found the problem though: The problem is the fuel pump relay sometimes does not energize when you turn the key on, and therefore the engine is not priming. So, I replaced the relay. Still not working. I check all the wiring to the relay, I even bypassed some of the factory wiring, cut the factory connectors off and spliced on a new plug for the relay. Still not working. After some research, I found out that the relay is grounded through the computer. Basically, one side of the coil is connected to the positive battery terminal at all times. When the computer grounds out the other side, the relay is energized. When the computer does not ground out the other side, the relay is de-energized. I ran a new wire from the relay to the computer. STILL not working. arrgh! So, I replaced the whole computer and....yep, STILL not working!!
Then I remembered I've had problems with relays in this truck before. Could it be some OTHER relay is the problem? In the fuse box, right next to the fuel pump relay, is the ECU relay. Hmm, if the ECU relay is bad, the ECU won't turn on. If the ECU won't turn on, it won't ground out the fuel pump relay. If it won't ground out the fuel pump relay...I'm going to get another relay tonight and replace the ECU relay. If that doesn't fix it, nothing will. While I'm at it, I'm replacing ALL relays in that box! This truck is getting dangerously close to getting sold. If I can't get this problem figured out, it's gonna have to go. My mom was stranded fo 2 hours yesterday before my uncle came and picked her up. Even worse, she's borrowing my cars now.
Then I remembered I've had problems with relays in this truck before. Could it be some OTHER relay is the problem? In the fuse box, right next to the fuel pump relay, is the ECU relay. Hmm, if the ECU relay is bad, the ECU won't turn on. If the ECU won't turn on, it won't ground out the fuel pump relay. If it won't ground out the fuel pump relay...I'm going to get another relay tonight and replace the ECU relay. If that doesn't fix it, nothing will. While I'm at it, I'm replacing ALL relays in that box! This truck is getting dangerously close to getting sold. If I can't get this problem figured out, it's gonna have to go. My mom was stranded fo 2 hours yesterday before my uncle came and picked her up. Even worse, she's borrowing my cars now.
The ECU could be missing an input in order to ground the fuel pump. Ignition switch? Security? Further diagnostics are required.
Originally Posted By: Warstud
Is this problem only at startup or will it shut off while driving?
Only at atartup. It's never shut off while driving.
Is this problem only at startup or will it shut off while driving?
Only at atartup. It's never shut off while driving.
Originally Posted By: exranger06
Originally Posted By: Warstud
Is this problem only at startup or will it shut off while driving?
Only at atartup. It's never shut off while driving.
Since that's the case... It sounds more likely to be a fuel problem to me. Possibly a weak fuel pump which will only get worse over time. Try cranking it with the gas pedal to the floor to see if it make a difference.
Originally Posted By: Warstud
Is this problem only at startup or will it shut off while driving?
Only at atartup. It's never shut off while driving.
Since that's the case... It sounds more likely to be a fuel problem to me. Possibly a weak fuel pump which will only get worse over time. Try cranking it with the gas pedal to the floor to see if it make a difference.
The problem is getting the fuel pump to turn on, not lack of pressure. I can hotwire the pump to the battery and it will turn on EVERY time. I hook it up the way it's supposed to with the relay, and sometimes it doesn't turn on at all. If you turn on the ignition and don't start the engine, you're supposed to hear the pump turn on for a few seconds. Sometimes you hear it turn on, sometimes you don't. If you don't, it will not start. If it does turn on like it's supposed to, it will start. Every time.
I just pulled the ECU relay and tried to start it, just to se what would happen. I get the exact same symptoms I've been getting. No fuel pump prime, and no start. Dash lights still light up. I have a new relay on there now. I think I finally got this solved.
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