Can a weak fuel pump really cause misfire?

[avacado11]

New motorcraft pump in today. New Bosch injectors in. New intake manifold gaskets. Cleaned the throttle body while I was at it(tons of carbon caked on the back, sealing off the gap on the throttle plate). Hooked everything up -> turn key -> pump primes -> long crank no start AGAIN. After a few attempts it did fire up for about 2 seconds then ran out of fuel and shut off. Fuel system shows “open loop” but I believe that was from when I tested the connector without the pump plugged in. It wasn’t an active code.

Inspected all wiring, including the one under the intake manifold where the rodents nest was. No damage. The ground for the fuel pump module - right Above the spare tire - is pretty corroded. Still solid, but I suspect that’s the issue. Will repair tomorrow, then see if it does anything. Also need to figure out the relay diagram so I can test for voltage there.

At this point, all that’s left is a bad ECU not sending the correct power out or there’s an issue with the wiring/ground.

Slight possibility that it could be the aftermarket remote start system the PO had installed. I totally forgot about it because I put the fobs into a drawer the second I got home. I hate aftermarket systems because of the issues they can cause.

Anyways, I atleast know it’s an electrical problem now. Worse case I will run a new wire from the box all the way to the connector. A new harness isn’t all that expensive but I’m not trying to unplug 20 connectors and fish the harness to the back of the truck.

 

[wtd]

Definitely test the ground before you drop the tank. Don’t make the same mistake I did.

What you could do is send 12v directly to the pump and see if your pressure goes up. Assuming you can reach the connector with the tank still mounted. 12v direct and No pressure = bad pump.

My old delphi pump would run off 12v directly but I suspected there was probably an internal failure with the backflow valve which is why I replaced it again. I think the delphi pump I got it with only lasted about 2 years though. It’s a 2014 and factory powertrain warranty would’ve only ended in mid 2019/100k. That pump I originally pulled out couldn’t have been that old considering it’s only been 19k/3.5 years since expiration.

I did some more testing yesterday and today and am convinced it's a bad pump. I tested the output from the ECM to the fuel pump relay control side and my test light would come on for the 2 second prime so I know the ECM was sending the correct signal. I tested all of the powers and grounds at the relay and they were good. I also tested power and ground at the pump with a multimeter and have a full 12.56V on the power wire and 0 on the ground.

I jumped pins 87 & 30 at the relay which sends direct power to the pump and it does not come on. It also doesn't come on for the 2 second prime.

I'm sorry to hear that you have still not gotten yours fixed. Did you check that connector behind the passenger side kick panel like in the video that I posted?

 

[wtd]

New motorcraft pump in today. New Bosch injectors in. New intake manifold gaskets. Cleaned the throttle body while I was at it(tons of carbon caked on the back, sealing off the gap on the throttle plate). Hooked everything up -> turn key -> pump primes -> long crank no start AGAIN. After a few attempts it did fire up for about 2 seconds then ran out of fuel and shut off. Fuel system shows “open loop” but I believe that was from when I tested the connector without the pump plugged in. It wasn’t an active code.

Inspected all wiring, including the one under the intake manifold where the rodents nest was. No damage. The ground for the fuel pump module - right Above the spare tire - is pretty corroded. Still solid, but I suspect that’s the issue. Will repair tomorrow, then see if it does anything. Also need to figure out the relay diagram so I can test for voltage there.

At this point, all that’s left is a bad ECU not sending the correct power out or there’s an issue with the wiring/ground.

Slight possibility that it could be the aftermarket remote start system the PO had installed. I totally forgot about it because I put the fobs into a drawer the second I got home. I hate aftermarket systems because of the issues they can cause.

Anyways, I atleast know it’s an electrical problem now. Worse case I will run a new wire from the box all the way to the connector. A new harness isn’t all that expensive but I’m not trying to unplug 20 connectors and fish the harness to the back of the truck.

I forgot to mention that on most four pin relays, pins 30 and 87 are the load side and pins 85 & 86 are the control side of the relay. Either pin 30 or 87 should have a hot all of the time fuse powering it up. 85 or 86 will be the ground and whichever one is not the ground will be the signal wire from the ECM or in your case maybe the FPCM depending on how the system is setup. This pin is where you can test to see if you are getting the power from the ECM.

When the relay receives the signal from the ECM or possibly FPCM, it will go to ground and close the switch inside the relay to connect pins 30 & 87 and that will send your power down to the fuel pump. This is a simplified explanation of how a relay works.

Typically if you jumper pins 30 and 87 together with a fused jumper, this will send direct power to the fuel pump without having to use the ignition switch and starter. You really need to have a wiring diagram before you do any jumper wires because you can cook the ECM if you jumper the control pin from the ECM to power.

When you test for power and ground at the fuel pump connector, you really want it to be plugged in to the fuel pump and use a back probe on the power and then ground wire at the connector to verify if you have both. If you do use a jumper wire on pins 30 and 87 in the fuse box, don't use anything larger than the size pins that the relay has so you don't spread apart the female terminals inside the fuse box.

I use this kit to do all of my jumping of relays. It's expensive though.

https://www.amazon.com/Lisle-69300-Master-Relay-Test/dp/B00CRQSYY4/ref=sr_1_1?crid=3HR0SEEXFC0K6&keywords=lisle%2Bmaster%2Brelay%2Btest%2Bkit&qid=1672339756&sprefix=Lisle%2Bmaster%2Brel%2Caps%2C147&sr=8-1&ufe=app_do%3Aamzn1.fos.18ed3cb5-28d5-4975-8bc7-93deae8f9840&th=1

I believe this blue one is what you need for your truck because my kit says it's for Ford but you would have to verify. You could make up your own fused jumper wires to use with it.

https://www.amazon.com/Lisle-69300-Master-Relay-Test/dp/B00CRQSYY4/ref=sr_1_1?crid=3HR0SEEXFC0K6&keywords=lisle%2Bmaster%2Brelay%2Btest%2Bkit&qid=1672339756&sprefix=Lisle%2Bmaster%2Brel%2Caps%2C147&sr=8-1&ufe=app_do%3Aamzn1.fos.18ed3cb5-28d5-4975-8bc7-93deae8f9840&th=1

 

[Jetronic]

I did some more testing yesterday and today and am convinced it's a bad pump. I tested the output from the ECM to the fuel pump relay control side and my test light would come on for the 2 second prime so I know the ECM was sending the correct signal. I tested all of the powers and grounds at the relay and they were good. I also tested power and ground at the pump with a multimeter and have a full 12.56V on the power wire and 0 on the ground.

I jumped pins 87 & 30 at the relay which sends direct power to the pump and it does not come on. It also doesn't come on for the 2 second prime.

I'm sorry to hear that you have still not gotten yours fixed. Did you check that connector behind the passenger side kick panel like in the video that I posted?

for stuff like this, use a high pwer test bulb, like a headlight. If it's not shining with full brightness you know there's an issue. A regular test light might not draw enough amps to show resistance in the wiring.

Though in this case the voltage drop shows the lines are good.

 

[wtd]

Update on mine. Installed a new pump and filter and now it runs. Hopefully this Delphi pump will last longer than two years and 11,000 miles.

 

[350Rocket]

I'm not sure who makes Spectra premium pumps but that is what was installed in my 05 Silverado at about 160k miles (80k miles and 5 or 6 years ago) when the original sending unit rusted out and leaked fuel. So far now signs of trouble with it.

 

[wtd]

I'm not sure who makes Spectra premium pumps but that is what was installed in my 05 Silverado at about 160k miles (80k miles and 5 or 6 years ago) when the original sending unit rusted out and leaked fuel. So far now signs of trouble with it.

Normally Delphi pumps are supposed to be good but who knows.

 

[350Rocket]

I'm not sure who makes Spectra premium pumps but that is what was installed in my 05 Silverado at about 160k miles (80k miles and 5 or 6 years ago) when the original sending unit rusted out and leaked fuel. So far now signs of trouble with it.

Sorry, no signs of trouble. Not now signs.

 

[brianl703]

Normally Delphi pumps are supposed to be good but who knows.

They're Chineseium like the rest. TI Automotive (fka Walbro) still makes at least some of their pumps in the USA, but at double the price.

 

[wtd]

They're Chineseium like the rest. TI Automotive (fka Walbro) still makes at least some of their pumps in the USA, but at double the price.

The Delphi pump was $146 two years ago when we bought the first one. Currently they are about $369 for the same pump. I'm glad it was under warranty.

Most aftermarket electrical parts are junk these days along with some OEM.

 

[avacado11]

Ok so after 3 days of rather intense diagnostics(including pulling the ECU apart to make sure nothings physically blown) the issue is fixed for the most part.

It was most likely a combination of things. Still have no clue what it exactly was but atleast the trucks running now so I rather not think about it.

The big break through today was the MAF sensor. I had replaced it with a Duralast last week after seeing the original motorcraft MAF was reading 2.xx g/s key on, engine off. A friend has the same truck and I compared it to his MAF sensor and his was 0.00 then 5.xx+ when the engine was cranked. Figure if my OEM MAF is reading air when the engine wasn’t running it had to be that right? Wrong. A winter storm had came through that day so I ran to Autozone real quick to pick up a new MAF. Installed, data was in line with my friends truck but it still wasn’t turning on.

Fast forward a few days I purchased a motorcraft fuel pump driver module, installed and the truck still wouldn’t start.

So I start testing the whole harness - all wires were good.

i pull the ECU cover off to see if anythings visually broken - all is good.

Put the truck back together, bypassed FPDM at the rear, and truck would start only if the gas pedal was depressed all the way down. Wouldn’t stay running but it would atleast fire up. Ran very rich(returnless fuel system, so needs FPDM to throttle fuel pump) to the point where smoke was pouring out of the intake tube. Ended up having to change the oil because of how much fuel was dumped into the engine.

Fast forward today, i about threw in the towel. Noticed a rusty ground for the harness running to the rear(right behind the driver headlight). Cleaned ground still no start. There is a connector right above the driver side wheel which is the harness that runs to the rear of the vehicle(including anything related to fuel). Unplugged it, plugged back in, truck started up but was misfiring at idle. Pulled fuel relay/fuse to clear out the extra gas that was dumped in when I bypassed the module. It started up but still missed at idle. Put the factory MAF sensor back and the truck started up and idled perfect.

Now it just misses at redlights but once the truck is moving it doesn’t shake. Looks like a new Motorcraft MAF sensor is the solution.

What sucks was that when I was running the OEM MAF I had a dorman FPDM installed. When my motorcraft FPDM came I was already on the Duralast MAF. Now I know to only buy OEM parts. The amount of misery these aftermarket parts have put me through is insane, especially considering the OEM parts only costed a $20-30 more(besides the Fuel pump, which was $500 instead of $180 Delphi). But that was kinda worth it because the tank is a PITA to drop.

 

[avacado11]

Update on mine. Installed a new pump and filter and now it runs. Hopefully this Delphi pump will last longer than two years and 11,000 miles.

Surprisingly I think who ever makes delphi pumps are the same people making Motorcraft pumps. Unless it is a direct clone. Both were made in Mexico. But, the delphi I got from autozone(same part #) was made in China and had a completely different design. I would say the Chinese one was better. The hoses had a sheathing over them, the connectors were much more robust, the pump had a cover over it. It was so different I questioned wether or not Rock Auto sold me a fake Delphi.

I put my motorcraft pump right next to the old delphi that I pulled out and everything was the same down to the wiring gauge/color, connectors, and hoses.

Infact, the fuel pump harness side connector is actually a universal style that’s shared with most domestic vehicle fuel pump assemblies. 4 pin with a red locking tab. I had thought my connector was broken so I searched for a new plug. It’s the same as the multi vehicle fit ones off Amazon.

 

[Bladecutter]

Now I know to only buy OEM parts.
The amount of misery these aftermarket parts have put me through is insane, especially considering the OEM parts only costed a $20-30 more...

You were asked in post #11 if the part was aftermarket or OEM.
You didn't reply with the fact that you were using Dorman parts until post #21.
In post #26 someone replied that the Dorman part was probably part of the problem.
And it wasn't until post #71 that you finally learned that lesson.

But, the delphi I got from autozone(same part #) was made in China and had a completely different design.
I would say the Chinese one was better.

Nope, you unlearned that lesson pretty quickly.

If the pump never worked right when you installed it, then it can't possibly be better, can it?

 

[350Rocket]

Ok so after 3 days of rather intense diagnostics(including pulling the ECU apart to make sure nothings physically blown) the issue is fixed for the most part.

It was most likely a combination of things. Still have no clue what it exactly was but atleast the trucks running now so I rather not think about it.

The big break through today was the MAF sensor. I had replaced it with a Duralast last week after seeing the original motorcraft MAF was reading 2.xx g/s key on, engine off. A friend has the same truck and I compared it to his MAF sensor and his was 0.00 then 5.xx+ when the engine was cranked. Figure if my OEM MAF is reading air when the engine wasn’t running it had to be that right? Wrong. A winter storm had came through that day so I ran to Autozone real quick to pick up a new MAF. Installed, data was in line with my friends truck but it still wasn’t turning on.

Fast forward a few days I purchased a motorcraft fuel pump driver module, installed and the truck still wouldn’t start.

So I start testing the whole harness - all wires were good.

i pull the ECU cover off to see if anythings visually broken - all is good.

Put the truck back together, bypassed FPDM at the rear, and truck would start only if the gas pedal was depressed all the way down. Wouldn’t stay running but it would atleast fire up. Ran very rich(returnless fuel system, so needs FPDM to throttle fuel pump) to the point where smoke was pouring out of the intake tube. Ended up having to change the oil because of how much fuel was dumped into the engine.

Fast forward today, i about threw in the towel. Noticed a rusty ground for the harness running to the rear(right behind the driver headlight). Cleaned ground still no start. There is a connector right above the driver side wheel which is the harness that runs to the rear of the vehicle(including anything related to fuel). Unplugged it, plugged back in, truck started up but was misfiring at idle. Pulled fuel relay/fuse to clear out the extra gas that was dumped in when I bypassed the module. It started up but still missed at idle. Put the factory MAF sensor back and the truck started up and idled perfect.

Now it just misses at redlights but once the truck is moving it doesn’t shake. Looks like a new Motorcraft MAF sensor is the solution.

What sucks was that when I was running the OEM MAF I had a dorman FPDM installed. When my motorcraft FPDM came I was already on the Duralast MAF. Now I know to only buy OEM parts. The amount of misery these aftermarket parts have put me through is insane, especially considering the OEM parts only costed a $20-30 more(besides the Fuel pump, which was $500 instead of $180 Delphi). But that was kinda worth it because the tank is a PITA to drop.

That's a good reason to diagnose before throwing the parts cannon at it. Any new part could be defective, especially aftermarket but even OEM parts. Best to only replace one thing at a time if you're going to trial and error instead of diagnose. And if it doesn't fix it out the old part back on and continue on.

 

[wtd]

Surprisingly I think who ever makes delphi pumps are the same people making Motorcraft pumps. Unless it is a direct clone. Both were made in Mexico. But, the delphi I got from autozone(same part #) was made in China and had a completely different design. I would say the Chinese one was better. The hoses had a sheathing over them, the connectors were much more robust, the pump had a cover over it. It was so different I questioned wether or not Rock Auto sold me a fake Delphi.

I put my motorcraft pump right next to the old delphi that I pulled out and everything was the same down to the wiring gauge/color, connectors, and hoses.

Infact, the fuel pump harness side connector is actually a universal style that’s shared with most domestic vehicle fuel pump assemblies. 4 pin with a red locking tab. I had thought my connector was broken so I searched for a new plug. It’s the same as the multi vehicle fit ones off Amazon.

The Delphi pump we used came from Autozone as well. I probably would not have used another one but it had a lifetime warranty on it and I couldn't find an AC-Delco pump for it online. We didn't check the Chevy dealer though. Hopefully it lasts longer than the last one.

 

[weaponoffreedom]

I think this thread has jinxed me. Yesterday my fiancé's younger son calls and says he is broke down. His truck won't start.

I go and pull the truck home. It's a crank, no start. I put a fuel gauge on it and it has 0 fuel pressure but does have fuel at the Shrader valve. When you turn the key on you can hear the pump prime if you are under the truck but no pressure.

We put a new Delphi pump in this truck a little over two years ago and about 11,000 miles ago and a new fuel filter.

I did some testing today and it has all of the correct inputs at the fuel pump relay and I swapped in the relay out of my 98 Chevy truck which uses the same relay but no luck. I can see the ground wire on the frame at the back of the truck and using a power probe, it shows a ground on the eyelet but I never could get it to light up and beep on the stud itself even after I took it off and cleaned everything.

I'm guessing the pump is bad but I'm still not sure about that ground at the frame so I will have to try some more testing tomorrow on that.

What about the fuel pressure regulator?

 

[dfarr67]

You know- I always avoided Walbro simply because of its unfortunate name (sounds like a toy) but a few years ago I replaced a noisy Carter with a 255gph unit and I would use them again- can't hear it at all. Only downside is I lost the check valve so it needs to prime first after sitting.

 

[wtd]

What about the fuel pressure regulator?

That wasn't the issue in this case. The fuel pump was dead. Power and ground to the pump were good but it wasn't coming on. New fuel pump fixed the problem.

 

[avacado11]

That's a good reason to diagnose before throwing the parts cannon at it. Any new part could be defective, especially aftermarket but even OEM parts. Best to only replace one thing at a time if you're going to trial and error instead of diagnose. And if it doesn't fix it out the old part back on and continue on.

It’s funny because I checked data logs and the OEM MAF sensor was reading air supply while the engine was off - so that was suspect. Since all dealers were closed that day I said heck why not run down the street and throw in a new Autozone MAF sensor. Sensor goes in - check data - reading correct(0.00g/s and 5.xx when cranking) so figure it’s working correctly.

That’s what threw me off. I don’t have software to run tests on the MAF sensor but even if I did it probably wouldn’t have the proper data to compare it off of.

The only thing I probably didn’t need was the $500 motorcraft FP. Original one definitely had a bad pump. Probably could’ve gotten away with the $50 delphi I installed the first time around. The $200 Injectors can be considered preventative maintenance and I was already pulling the manifold to clean out a nest anyways so that’s not too bad.

Atleast now I know bad MAF sensors don’t always throw a code.

 

[weaponoffreedom]

It’s funny because I checked data logs and the OEM MAF sensor was reading air supply while the engine was off - so that was suspect. Since all dealers were closed that day I said heck why not run down the street and throw in a new Autozone MAF sensor. Sensor goes in - check data - reading correct(0.00g/s and 5.xx when cranking) so figure it’s working correctly.

That’s what threw me off. I don’t have software to run tests on the MAF sensor but even if I did it probably wouldn’t have the proper data to compare it off of.

The only thing I probably didn’t need was the $500 motorcraft FP. Original one definitely had a bad pump. Probably could’ve gotten away with the $50 delphi I installed the first time around. The $200 Injectors can be considered preventative maintenance and I was already pulling the manifold to clean out a nest anyways so that’s not too bad.

Atleast now I know bad MAF sensors don’t always throw a code.

And everything is suspect if the computer is messed up...........one day I hope it comes full circle and we get rid of all the BS in vehicles.