Dropping fuel pressure and goes into limp mode?

BULLITT1939

MEMBER
1999 FORD MUSTANG
4.6L
V8
2WD
MANUAL
20,000 MILES

The car is running about 20-29 lbs of fuel pressure under a load it drops and goes into limp mode. If you stop and restart it resets itself. It’s a 1999 Saleen so basically a supercharged setup. It has two Bosch 130 fuel pumps. Just changed them for new ones today. New fuel filter. New fuel pressure regulator. Traced vacuum lines today and found a few issues. I put new vacuum plugs that were cracked. It was throwing a P0190. I cleared it and haven’t come back. Any help or suggestions would be appreciated.

7 Replies

KEN L

MASTER CERTIFIED MECHANIC
47,651 POSTS

It has two Bosch 130 fuel pumps? Is this some kind of race application? If the fuel pump is good then it could be the fuel sock at the pump is clogged or you have a bad fuel pump, it is a deadhead system so there is no regulator which only leaves the fuel pump as being bad. Here is how a stock application is changed out. the video shows how to drain the tank:

https://youtu.be/Q5MH2gnyFH0

Check out the images (below). Let us know what happens and please upload pictures or videos of the problem.

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Monday, February 6th, 2023 AT 11:02 AM

BULLITT1939

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It’s 2 brand new pumps, the same ones that came out of it. New pumps, new socks, fuel filter and fuel pressure regulator. The tank was dropped and cleaned out yesterday. Have the same issue as before all this was changed.

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Monday, February 6th, 2023 AT 11:37 AM

KEN L

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Are you sure the gauge is correct? It is a deadhead system so there is not to much to it. Pump and power, can you confirm you have 12 volts to the pump? Here is a guide to help and the fuel pump power wire color (red/blk) so you can do the test.

https://www.2carpros.com/articles/how-to-use-a-voltmeter

If the voltage is low, I would change out the fuel pump control module and check the ground as well. Check out the images (below). Please let us know what you find.

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Tuesday, February 7th, 2023 AT 11:30 AM

BULLITT1939

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33 POSTS

We found the issue. Thanks for the input!

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Sunday, February 26th, 2023 AT 6:11 AM

KEN L

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What was it, can you please tell us?

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Monday, February 27th, 2023 AT 8:20 AM

BULLITT1939

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33 POSTS

Well, the car had been modified with a dual set up no longer made. So after initially changing the pumps, we checked all the vacuum lines and found a few issues there. We addressed these, but the car was still not running up to par. We dropped everything again and changed all the old hoses as well as noticed one of the parts was put back incorrectly. It looked like it only fit one way, but you had to route it a different way. We have a collection of Mustangs, but none of them had this set up so it was definitely a learning experience. Glad to report all is well now and we upgraded to larger pumps after dropping it the second time!

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Friday, March 24th, 2023 AT 4:59 PM

KEN L