Intermittent abrupt power loss

[Dudeth]

Once or twice a day my 02 Expy with 4.6L randomly loses power. It cuts out for about a second or less and then everything is normal. It seems to mainly happen when accelerating from being stopped. It almost seems like the fuel pump loses pressure for a second but I had the pump and the fuel filter replaced about 5 months ago. If there wasn't a coil on each spark plug I would think that the coil was shorting out for a second. It's like there is no spark at all for a second or no fuel pressure. Coil packs were replaced about a year ago. It doesn't seem like a miss on one cylinder, seems like total power loss. Any ideas?

 

[1955moose]

Any dimming of gauges when this happens? Could be battery or cables losing connection, then making connection. I'd do the usual, codes, fuel pressure test. Might want to check out maf sensor plug/ connection. Something stupid will rear its head. Is engine power OK otherwise?

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[ExplorerTom]

Ignition switch- how heavy is your key ring hanging off the ignition key?

Sounds unlikely, but I know a guy who had a massive key ring on his S2000 and it would cut out slightly at the track coming out of corners. Once he ditched the crap, problem went away.

 

[Dudeth]

Any dimming of gauges when this happens? Could be battery or cables losing connection, then making connection. I'd do the usual, codes, fuel pressure test. Might want to check out maf sensor plug/ connection. Something stupid will rear its head. Is engine power OK otherwise?

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I replaced the battery last week, connections are good. I haven't noticed any dimming of gauges or anything but then again I'm not sure if it's happened at night yet. There's no CEL, and power is great otherwise.

 

[Dudeth]

Ignition switch- how heavy is your key ring hanging off the ignition key?

Sounds unlikely, but I know a guy who had a massive key ring on his S2000 and it would cut out slightly at the track coming out of corners. Once he ditched the crap, problem went away.

Veeery interesting. My key ring isn't massive but there is some weight to it. I'll eliminate that variable and see what happens.

 

[1955moose]

Does your Suv make a sputtering like starving for fuel? Or is it a bucking feeling like flicking off/on, like a wall light switch?

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[blackburb]

Off like a switch? Hit the gas and nothing happens for 1/2 a second? Mine does the same. Is it from a complete stop or as you're rolling to a stop but hit the gas before completely stopped? I have a theory. The injectors are off while coasting but are supposed to come on when speed drops below a preset minimum. I think it's just a hiccup in energizing the injectors after coast.

 

[docraymund]

Wiring of MAF or TPS need to be checked especially in areas where they might chafe against the engine or chassis.

 

[Engineer1225]

Once or twice a day my 02 Expy with 4.6L randomly loses power. It lcuts out for about a second or less and then everything is normal. It seems to mainly happen when accelerating from being stopped. It almost seems like the fuel pump loses pressure for a second but I had the pump and the fuel filter replaced about 5 months ago. If there wasn't a coil on each spark plug I would think that the coil was shorting out for a second. It's like there is no spark at all for a second or no fuel pressure. Coil packs were replaced about a year ago. It doesn't seem like a miss on one cylinder, seems like total power loss. Any ideas?

Have you checked ALL the grounding bolts for corrosion? Have you also checked the fuel pump relay in the battery junction box? I recently cleaned my Expeditions grounding bolts; the ones coming off the ECM, the ones going to the frame, engine, etc. They were HEAVILY corroded. There was almost no metal left making contact, just corrosion. I was getting a IAT sensor error code, but I checked the reference voltage and it was fine. The faulty ground was the problem. Also had issues similar to what you are describing. Turns out my fuel pump relay was going bad. You should switch the relay from your wiper blades and fuel pump and see if this fixes the problem. The ECU, Wiper Blades, and Fuel Pump, should all use the same relay part. You should be glad you don't have an 03+. Their battery junction box isn't as simple as ours, they have a PCB battery junction box that eventually goes bad near the Relay solder joint areas.

 

[soylentgreen]

When you say power...you mean electrical power or engine power?

If you're saying engine power, I agree with docraymund. Could be a throttle position sensor has a bad spot on it or a lose connection or a short in the wiring.

 

[Club Expo]

Mine des this , but honestly only when there is like a 1/4 tank of fuel . I always thought it was from fuel sloshing .. Mine won't do it when it has plenty of fuel. I could probably make mine do it . Come to an abrubt stop then punch the throttle. Ive learned to be easy when fuel is low

 

[1955moose]

If your experiencing problems with low fuel, its more likely a dirty screen/ pickup, or one of the hoses in tank are experiencing deteriation.

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[Dudeth]

Does your Suv make a sputtering like starving for fuel? Or is it a bucking feeling like flicking off/on, like a wall light switch?

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Like a light switch. It finally just died on me and won't start. A couple days ago I was driving down the freeway and it started losing power and died. Pulled over and restarted but it kept cutting out. Made it a little further down the road and it died and wouldn't start back up.

Off like a switch? Hit the gas and nothing happens for 1/2 a second? Mine does the same. Is it from a complete stop or as you're rolling to a stop but hit the gas before completely stopped? I have a theory. The injectors are off while coasting but are supposed to come on when speed drops below a preset minimum. I think it's just a hiccup in energizing the injectors after coast.

Yep, foot was on the gas and then it just completely lost power for a 1/2 second or so and then was fine. It's dead now. It seemed to mainly happen when taking off from a complete stop.

Have you checked ALL the grounding bolts for corrosion? Have you also checked the fuel pump relay in the battery junction box? I recently cleaned my Expeditions grounding bolts; the ones coming off the ECM, the ones going to the frame, engine, etc. They were HEAVILY corroded. There was almost no metal left making contact, just corrosion. I was getting a IAT sensor error code, but I checked the reference voltage and it was fine. The faulty ground was the problem. Also had issues similar to what you are describing. Turns out my fuel pump relay was going bad. You should switch the relay from your wiper blades and fuel pump and see if this fixes the problem. The ECU, Wiper Blades, and Fuel Pump, should all use the same relay part. You should be glad you don't have an 03+. Their battery junction box isn't as simple as ours, they have a PCB battery junction box that eventually goes bad near the Relay solder joint areas.

I'll definitely give all of that a check. Haven't had a chance to look at it yet but will run a fuel pressure test asap and swap the relays.

Thanks for your input everyone.

 

[Dudeth]

When you say power...you mean electrical power or engine power?

If you're saying engine power, I agree with docraymund. Could be a throttle position sensor has a bad spot on it or a lose connection or a short in the wiring.

Engine power, I should have been more descriptive. Electrical power doesn't seem to be disrupted at all.

Mine des this , but honestly only when there is like a 1/4 tank of fuel . I always thought it was from fuel sloshing .. Mine won't do it when it has plenty of fuel. I could probably make mine do it . Come to an abrubt stop then punch the throttle. Ive learned to be easy when fuel is low

I guess this is possible, but I changed the fuel pump recently.

If your experiencing problems with low fuel, its more likely a dirty screen/ pickup, or one of the hoses in tank are experiencing deteriation.

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It has a new screen on it, like 4 months old. But it could be fuel system related.

 

[Dudeth]

Does anyone have a source for all of the wiring diagrams for my vehicle?

 

[1955moose]

I have wiring for 2000, but might be different. As far as a bad tps switch. Tap into the wire on the tps that reads voltage swing while operating throttle. Voltage should start around 1 volt, and smoothly move up to 4.5 to 5 volts. If the voltage gets jumpy or drops as your operating throttle, then your switch is bad. Their tough to remove due to lock tite on screws, so be sure.

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[Dudeth]

Swapped the fuel / wiper relay, no change. Checked fuel fuses, no issues there. Put a fuel pressure loan a tool on there and have 0 fuel pressure. I'm leaning towards the fuel pump again. This will have been the 3rd one in a year and a half. If for some reason the fuel pump isn't getting enough current will it cause it to burn out?

 

[Dudeth]

I had the transmission rebuilt by a family friend about a year and a half ago. I can't remember if the engine wouldn't start after the rebuild or if the transmission wasn't behaving correctly but he figured out that the new tech had pinched the wiring harness in between the trans and motor when reinstalling. He had to run a wire from the fuse box to the transmission since one wire got cut due to the pinching. The wire runs to fuse 18 in the engine compartment fuse box which is the PCM/Fuel Injector/ fuel pump / MAF fuse. Could this be causing an issue with the fuel pumps? There is a separate fuse for the fuel pump, fuse 10 which seems to be the main power for the fuel pump.

Could this wire the trans shop added be causing fuel pump issues?

I'm trying to figure out how to check power to the fuel pump without having to try to get to the connector at the gas tank. I haven't checked the inertia switch yet but I don't see why that would be the issue since I was driving down a smooth freeway when it died.

 

[1955moose]

Fuse #10 #18, and relay 301 are all for fuel pump in my 2000 owners book. That's for the under hood box. Maybe someone can say if 2002 is the same? What brand of pumps are you installing? If checking voltage at inertia shutoff switch it will read 12volts, then drop as you crank key, usually 6-9 volts. Same at pump itself. Power runs through relay then drops, because the computer, and power control module vary the amount of fuel depending on load of engine. Any corrosion on wires or connections will affect voltage/amperage making it to pump.

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[docraymund]

If your truck's fuel pump quickly dies out then you need to drop the tank and give it a thorough cleaning. Sediments and other debris might be present. Also examine the connectors for signs of overheating and replace them.