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87 B2 2.9 efi, misfires, lags with throttle

Posted: Sat Mar 10, 2012 11:23 pm
by CurtisP87
I'm having some problems with my bronco, and cant for the life of me figure out whats going on...When i turn the key it fires right up, no problems, every time. When idling its obvious that its missing on a cylinder or two. As soon as i touch the throttle, the rpms drop, motor begins shaking violently, and it sounds like its missing on three or four cylinders. Earlier today I replaced distributor cap, rotor, plugs/wires, throttle position sensor, HP fuel pump, and the filter down the line from it. Air filter is good....

I tested fuel pressure, via the schrader valve in fuel lines....35 psi at idle, and 40 psi when on throttle, despite the rough idle. This makes me think my fuel delivery is just fine (i.e. ruling out a problem with the low pressure pump or its filter), so its got to be a timing or spark issue. The plugs i took out earlier were all in o.k. shape, slightly corroded, but wet and gooey, like the engines been running rich.

Ive been doing some reading, and it almost sounds like I could have a faulty TFI. However, everything Ive been reading seems to imply that the engine should perform fine when cold, and the problems arise when it warms up, and Im having these problems when cold, the engine isnt running well enough for me to leave it on long enough to get hot.

Like i said, Im totally stumped....Has anyone else ever had similar problems?
Thanks in advance for any help or opinions!!

Re: 87 B2 2.9 efi, misfires, lags with throttle

Posted: Sun Mar 11, 2012 8:40 am
by drofman
many parts store can test you TFI. i would go from there. fuel pressure is good. plugged exhaust? timing with the spout removed?

Re: 87 B2 2.9 efi, misfires, lags with throttle

Posted: Sun Mar 11, 2012 9:54 am
by CurtisP87
When I remove the spout the engine runs smoothly, which is why Im leaning towards the TFI as my culprit. I cant take it to a parts store since as soon as I give it throttle it wants to die, not even enough power to spin the wheels. I have a spare TFI that was given to me by the previous owner when i purchased the truck, so my next plan of attack is to try remounting it somewhere and see if that helps at all.

Re: 87 B2 2.9 efi, misfires, lags with throttle

Posted: Fri Jul 10, 2020 3:00 am
by Sailorsoul
Hi new here but I'm having the same exact problem and I cant for the life of me figure out what is going on, so 86 2.9 new fuel pump, pressure regulator, 30 psi at idle, it starts tight up but as soon as I give it gas it Boggs down and backfires, dev running rich, I can smell it took timing cover off I'm about to replace the chain and h2o pump tomorrow, I pulled codes with a reader and I got 12, 24, 31, 25.
So 12 is cant control rpm
24 act/iat
31 evap sensor
25 is nick sensor
So I obviously went for the nock sensor and I tested it with a multi meter on a vice and a hammer and it still works so not it's not the sensor, and tested the small wire harness and it's good, distributor cap, rotor is also new and I thin the distributor is new too, just bought it and I'm trying to figure it out on how to get it back on the road thank you in advance