EFI Guru Help- Backfire

[Killer Frogs]

I have a '73 Bronco that I did an engine swap on. The donor engine is junkyard 5.0 from a 2000 Ford Explorer. I removed and cleaned the heads and installed all new gaskets. I am using a high and low pressure fuel pump with an accumulator for the fuel pressure return line. The high pressure pump is 40PSI. Since the Explorer's fuel rail did not have a return line I used one from a 87-93 Mustang. I had the wire harness modified and the ECU reprogrammed to take out the emissions and other things not needed, thank you EFI Guy! The transmission is a 5 speed NV3550.

The engine ran fine for probably about 10 miles. The first 3 miles was to an exhaust shop to put in the exhaust, straight headers were LOUD! I'm not sure what happened, but it quickly developed a backfire. At idle it does not backfire, but does at about 30-40 mph. I have a basic Harbor Freight code reader and it was giving me a code that I can't remember. But it was something with the coil and #1 cylinder. I swapped the coil thinking the code would move to the other side, but the code stopped coming up, but it didn't fix the backfire.

In addition to the backfire, the engine runs rough. I had one mechanic think it was because the air filter was getting too much air from the cooling fan where the MAF could not keep up with the extra air coming from the fan. I added the license plate to block the air, but that didn't help.

The only thing that has helped was checking the fuel injectors. One was clogged and I was able to clean it out. It reduced the frequency of the backfire, but did not fix it.

No vacuum leaks.

I'm wondering about fuel pressure. There is not a fitting on the rail to hook up a pressure gauge. I did replace the fuel pressure sensor. Pics are included, any suggestions?

 

[B RON CO]

Hi, often backfiring and popping is a lean condition. First I would check the firing order. Good luck

 

[surfer-b]

Not sure what setup you have but if its a stock 2000 Explorer it requires about 60 psi, my gauge reads ~ 65psi consistent. you can add a pressure gauge where the Schrader valve is on the fuel rail.

 

[Viperwolf1]

Not sure what setup you have but if its a stock 2000 Explorer it requires about 60 psi, my gauge reads ~ 65psi consistent. you can add a pressure gauge where the Schrader valve is on the fuel rail.

X2. Those smaller injectors require higher pressure.

I have a '73 Bronco that I did an engine swap on. The donor engine is junkyard 5.0 from a 2000 Ford Explorer. I removed and cleaned the heads and installed all new gaskets. I am using a high and low pressure fuel pump with an accumulator for the fuel pressure return line. The high pressure pump is 40PSI. Since the Explorer's fuel rail did not have a return line I used one from a 87-93 Mustang. I had the wire harness modified and the ECU reprogrammed to take out the emissions and other things not needed, thank you EFI Guy! The transmission is a 5 speed NV3550.

The engine ran fine for probably about 10 miles. The first 3 miles was to an exhaust shop to put in the exhaust, straight headers were LOUD! I'm not sure what happened, but it quickly developed a backfire. At idle it does not backfire, but does at about 30-40 mph. I have a basic Harbor Freight code reader and it was giving me a code that I can't remember. But it was something with the coil and #1 cylinder. I swapped the coil thinking the code would move to the other side, but the code stopped coming up, but it didn't fix the backfire.

In addition to the backfire, the engine runs rough. I had one mechanic think it was because the air filter was getting too much air from the cooling fan where the MAF could not keep up with the extra air coming from the fan. I added the license plate to block the air, but that didn't help.

The only thing that has helped was checking the fuel injectors. One was clogged and I was able to clean it out. It reduced the frequency of the backfire, but did not fix it.

No vacuum leaks.

I'm wondering about fuel pressure. There is not a fitting on the rail to hook up a pressure gauge. I did replace the fuel pressure sensor. Pics are included, any suggestions?

 

[904Bronco]

Mix and match parts here.

2000 Explorer had 17 lbs injectors that ran at 60 psi... Higher pressure with lower lbs injectors basically equated to 19 injectors.
Regulator was in the fuel pump assembly in tank.

So now you are running smaller injectors on a mustang fuel rail with a return, at a lower pressure. (Are you using Mustang fuel regulator too?)

Motor is running lean, worse under load and that is why it pops. You probably need to install 19 lbs injectors... But,

Did Garry set up your ECU for the Mustang return line style lower pressure or was he expecting you to use an Explorer fuel pump with higher pressures?

Nice clean install by the way... ;D

I am not an expert by any means, but I am working with a 2000 Explorer install myself and have learned a lot in speaking with Garry and doing a 98 Explorer in my 68. That an messing with Fox body Mustangs for a few years...

 

[needabronco]

Check for vacuum leaks on the bottom of the intake manifold. I chased a similar problem for longer than I care to admit, the solution was a vacuum port cap was cracked causing unmetered air to enter the intake manifold.

 

[Killer Frogs]

The firing order is correct, checked that several times.

I was guessing the fuel rail/injectors as the culprit. The fuel rail does not have a schrader valve to hook it up to, but I got the loan a tool from Auto Zone and it reads 43 psi! So the fuel pump is good. It looks like my injectors might be the culprit. I did tell Garry what fuel system I was running, but probably not the change in fuel rail.

Thanks for the complement on the clean install. My wife was always wondering about the parts hanging in our garage after painting!

 

[chuzie]

Im too am running explorer efi with Mustang rail / regulator and explorer injectors without issue at 40psi.



Sent from my GS3 on Cyanogenmod with the older / better version of Tapatalk!

 

[garberz]

Im too am running explorer efi with Mustang rail / regulator and explorer injectors without issue at 40psi.



Sent from my GS3 on Cyanogenmod with the older / better version of Tapatalk!

Are you running the earlier Explorer ECM that used the 19# injectors and lower fuel pressure?

Mark

 

[Killer Frogs]

Sounds like my problem is either injectors that are too small or not enough fuel pressure. The Fuel pressure regulator was preset at 40, but is adjustable.

https://www.summitracing.com/parts/pfs-10679

 

[904Bronco]

Sounds like my problem is either injectors that are too small or not enough fuel pressure. The Fuel pressure regulator was preset at 40, but is adjustable.

https://www.summitracing.com/parts/pfs-10679

Not sure what your pump is rated at... but quick and easy way would be crank up the fuel pressure to 60 and see if it runs better. Assuming your fuel system can handle it. Remember it is pressure and volume of fuel....

Kinda hard with no schrader valve though for a fuel pressure gauge

Still would like to hear how Garry set up your ECU and harness...

 

[Viperwolf1]

Sounds like my problem is either injectors that are too small or not enough fuel pressure. The Fuel pressure regulator was preset at 40, but is adjustable.

https://www.summitracing.com/parts/pfs-10679

There you go, crank it up to 65 psi.

17 lb/hr injectors at 65 psi flow equivalent to 24 lb/hr injectors at 40 psi.

 

[chuzie]

Are you running the earlier Explorer ECM that used the 19# injectors and lower fuel pressure?

Mark

Is there a listing identifying the applicable pcm codes?

Sent from my GS3 on Cyanogenmod with the older / better version of Tapatalk!

 

[garberz]

I would think EFIguy has compiled a list of all the Explorer PCM's. I know there are several different one's, and because they also control the trans and a few other things, they don't interchange very easy. Not like the OBDI PCM's.

Mark

 

[EFI Guy]

All 99-01 computers are set to run at 65 PSI. Get a gauge mounted somehow and crank it up to 65. Also remove the vacuum line from your regulator, it needs to be a constant 65 PSI and not change with engine vacuum.

99-01 PCM codes are EQE1-EQE5, and FLN0.

 

[Killer Frogs]

Fixed! I cranked up the regulator, pulled the vacuum line, and it is good. First attempt I got it up to 60 psi and it was close, but no backfire. A little more cranking and it is good. I need to get it on the highway to make sure. Thank you for the help!

 

[904Bronco]

Fixed! I cranked up the regulator, pulled the vacuum line, and it is good. First attempt I got it up to 60 psi and it was close, but no backfire. A little more cranking and it is good. I need to get it on the highway to make sure. Thank you for the help!

Easy fixes are always the best...