Bronco II 1988 2.9 engine hesitation warm and cold start up rough running

[IIBRONCOS]

Just recently I noticed at start up, a not as smooth as it used to be running engine. Once in a while it will start and be smooth as it warms, and sometimes it will start up fast
but feel rocky as it warms up. Even warm if I hit the gas quickly there is a hesitation before it revs up. It drives fine warm, but cold it is not smooth. Most engine parts were replaced about 20,000 miles ago. The 2 things that were not replaced are the TPS and IAC both which are original. I did clean the IAC 20,000 miles ago. It currently has about 63,000 original miles. Any ideas where to start would be appreciated.

 

[franklin2]

Check the sparkplug wires and see if they are rubbing anywhere. Easy for them to rub against the firewall.

 

[IIBRONCOS]

I checked the plug wires and found no rubbing. I removed all of the Autolite AP-105 spark plugs, and a couple had some wear at the tip but all looked to be normal.
I installed a new set of Autolite spark plugs AP-105, gapped at 44. I started the engine and it did not solve the rougher idle and slight hesitation when quickly accelerating in park. I put 2 different vacuum gauges on the engine, and one read 14.5 and the other was at 18. The needles were steady with a slight variation at idle. Any help is appreciated.

 

[Uncle Gump]

I always ask this when someone asks for help with diagnosis...

What's the fuel pressure?

It really is the simplest thing to check and is everything to the engines fuel delivery.

 

[IIBRONCOS]

I will work on getting a fuel pressure tester. Thanks

 

[IIBRONCOS]

Well I thought fuel pressure was an easy thing to check, but not so far. I rented a kit from Autozone and it was defective. I then ordered a kit only to find out it did not have the proper connections to fit the B2. I sent the kit back and am now going to take it in and have the fuel pressure checked. I did notice after cycling the pump a couple times, when I pressed on the schrader valve I did not get a strong stream of fuel coming out.

 

[Uncle Gump]

Dang... that's a string of bad luck. I had to replace mine and bought this one.

OTC Tools 5630 OTC Fuel Pressure Testers | Summit Racing

Free Shipping - OTC Fuel Pressure Testers with qualifying orders of $109. Shop Fuel Pressure Gauges, Engine Diagnostic at Summit Racing.

www.summitracing.com

 

[IIBRONCOS]

Thanks for the tip on the gauge. It would of been faster and easier for me just to replace the high pressure pump !!

 

[IIBRONCOS]

Found someone to do a pressure test on the fuel system, and the gauge read 29 lbs. Ordering a high pressure pump tonight.

 

[IIBRONCOS]

Installed a new high pressure pump. It is putting out 39 lbs of pressure at the rail. The B2 ran real smooth today. Thanks Uncle Grump for the telepathic diagnosis.

 

[Uncle Gump]

Well that's good...

It's really just where ya have to start. If the fuel pressure is off... nothing else works as it should.