help... I'm having trouble figuring out what's wrong with my 91 f150 4.9

Asked by Jun 23, 2015 at 02:05 AM about the 1991 Ford F-150 XLT Lariat 4WD SB

Question type: Maintenance & Repair

When I first crank it up it runs fine.
But after a few minutes it starts
bogging down and won't drive any
longer. I've put a new throttle
position sensor and air idle control
valve on it but that didn't change
anything. I've also looked for vacuum
leaks but can't find any. Any ideas on
what it could be? Any help is greatly
appreciated.

13 Answers

95,085

Have you checked exhaust system back pressure? The kit is available at most parts stores.

18,810

Could be a clogged catalytic converter have system tested with kit tennisshoes mentioned in his answer.

Oh yea, that's another thing I forgot to mention that I did. I cut the cat off too and that didn't do anything.

95,085

If the cat melted down then all of that crud winds up in the muffler and plugs it up but not enough to flow some, I would still test the back pressure.

18,810

Did you try starting the vehicle with the cat off ? Before you put a new one on.

Yes and that didn't change anything neither.

95,085

Ok so ruling out exhaust, then the fuel pressure and flow is next, replace the fuel filter before performing the test so you get a accurate reading, you should also watch for air in the fuel line, that could mean that there is a problem with the pump or connector hose inside the fuel tank. Have you tested for codes in the system? Go to: http://straighttalkautomotive.com/OBD1/ford-OBD-I.html that site has the codes and how to pull them yourself.

18,810

Just been thinking about something that happened to me awhile back. Looked at this F 150 forget the year for a guy who had the same problem as yours. I looked at that vehicle for almost two weeks before I had figured out what was going on. Let's just say I replaced a lot of parts on that vehicle before I found out what the problem was. The rubber gas line coming from the metal fuel rail to the connection to the fuel pump supply line on top of tank the rubber hose was collapsing. Dropped the gas tank low enough to see the the rubber line going to tank and watched as the hose started to collapse after vehicle run for about 5 minutes and watched it go back to normal after turning vehicle off . Replace that hose and and the problem was solved. Do not know if that is your problem but I would look into it if I was you.

Alright guys I'll check into that and let tall know how it goes. Thanks

I checked the fuel line and it didn't collapse. I have a 3 inch body lift so I didn't have to drop the tank

Ok so I unplugged the vacuum line going to the fuel pressure regulator while running and it started idling right. But when I plug it back in it bogs down. Bad fuel pressure regulator?

95,085

Possible, but it could also mean plugged fuel injectors, what was the fuel pressure.

I don't have a kit to test it I'll have to go get one tomorrow. Also replaced the fuel pressure regulator today

Your Answer

Add photo

Related Questions

  • help... I'm having trouble figuring out what's wrong with my 91 f150 4.9 13 answers

    When I first crank it up it runs fine. But after a few minutes it starts bogging down and won't drive any longer. I've put a new throttle position sensor and air idle control valve on it but that...

    1991 Ford F-150 XLT Lariat 4WD SB

    -

    Maintenance & Repair

  • Whats wrong with my F150 3 answers

    Ford F-150 XT 5.8L 4WD Automatic. This is a few fold question. 1st. My speedo, digital odometer, cabin lights, cruise control, aux lighter jack, and radio do not work in my truck anymore. This is bee...

    1992 Ford F-150 XL 4WD LB

    -

    Maintenance & Repair

  • I have a 1990 f150 with a 4.9 and I'm having electrical problems with my distributor 2 answers

    1990 Ford F-150 XLT Lariat LB

    -

    Maintenance & Repair

  • what is wrong with my f150 98 model 4.2 1 answer

    I recently went and got a half a ton of gravel in my truck. I shut the truck off by the ignition and loaded it. I then tried to start it back up and it wont start. I had to get someone to pull it ho...

    1998 Ford F-150

    -

    Maintenance & Repair

  • Trouble starting F150...NEED ADVICE/HELP! :P 3 answers

    I have an '87 F150 Str8 6 engine, & it has trouble starting after letting it sit after 10min. It starts right back up the minute u shut it off, or when it sits for a day..So far, I've given it a tune ...

    1987 Ford F-150

    -

    Maintenance & Repair

F-150

Looking for a Used F-150 in your area?

CarGurus has 207,301 nationwide F-150 listings starting at $1,499.

ZIP:

Search Ford F-150 Questions

Ford F-150 Experts

#1 OJ
OJ
Reputation 8,210
#2 dandyoun
dandyoun
Reputation 4,390
#3 tennisshoes
tennisshoes
Reputation 2,880
View All

Related Models For Sale

Used GMC Sierra 1500
762 Great Deals out of 69,121 listings starting at $1,850
Used Ford Mustang
543 Great Deals out of 45,845 listings starting at $1,999
Used Ford F-250
469 listings starting at $2,000
Used Ford Explorer
926 Great Deals out of 70,249 listings starting at $997
Used Ford Ranger
176 Great Deals out of 5,675 listings starting at $950

Used Cars For Sale

2018 Ford F-150 For Sale
51 listings starting at $35,135
2017 Ford F-150 For Sale
26 Great Deals out of 133,537 listings starting at $18,022
2016 Ford F-150 For Sale
86 Great Deals out of 13,559 listings starting at $18,300
2015 Ford F-150 For Sale
203 Great Deals out of 8,344 listings starting at $16,999
2014 Ford F-150 For Sale
383 Great Deals out of 12,684 listings starting at $6,600

Content submitted by Users is not endorsed by CarGurus, does not express the opinions of CarGurus, and should not be considered reviewed, screened, or approved by CarGurus. Please refer to CarGurus Terms of Use.