PDA

View Full Version : NEED DIAGNOSIS HELP! PLS!


bigrig81
05-12-2010, 10:28 AM
k so here's the deal, i have a 1990 F-150 302TBI. A while back i took out the single exhaust and made it dual in my shop. I kept the small cross tube between the two lines of exhaust that the O2 sensor, but i did eliminate what i am fairly positive is an EGR line that comes off the exhaust. the truck didn't run much for a couple months as well. and we did have the plugs out, but isn't contributing i don't think.

so here's the problems now.....

When i go to start the truck, it will turn over and over continuously without firing on the first turn of the key, but if i turn it over a couple seconds and then try again it will fire and die. if i try it again it will start. it's about the 3rd or 4th turn of the key it will fire and run. any added throttle kills it when starting and it also stalls very easy when it's cold. after the truck has fired once and ran even for a few seconds, i can turn it off and it will fire right up again with no hesitation. Also, when driving if i hit the throttle quickly it hugely hesitates and then goes. if I apply throttle slowly, no problem. (when it's running, it runs smooth not rough)

my best thought is too low a pressure in the fuel system.

if it was the EGR hose i left unattached (have left it open and plugged and makes no difference) i am pretty sure it would be a rough idling problem. unless.... does that line i think is the EGR cycle hot exhaust past the manifold to preheat the fuel like the exhaust bypass on the carbed engines? :dontknow:

HELP!

:D

radman
05-12-2010, 11:12 AM
sounds like a lack of fuel. i cant remember when they changed the fuel system, it was either 90 or 91 the older trucks had up to 3 pumps and 2 filters, most people change the filter near the firewall, but there is annother one in the botom of the tank selector valve with all the fuel lines running in and out of it, i would start there. the tube you disconnected from the exhost sounds like the one that takes the exhost gases and re burns it by pumping it back to the exhost ports in the head, mine rusted off a long time ago, never had a problem without it.

bigrig81
05-12-2010, 12:42 PM
ya i thought it was an EGR line, but wasn't 100% sure. as for the pumps and filters.... I only have a single tank bc it's a short box, but yes, i think we will be doing the filters asap and seeing if it helps.

other ideas?

Asshat
05-12-2010, 05:11 PM
the tank is the low pressure pump and on the rail is the high presure pump in front of that is the filter.between the tank and frame pump is usually a resevoir (for the dual tanks) it doesnt usually get plugged.I would check ur tps switch on the throttle body if it has one.the j yard is pretty cheap and if that cures the prob then buy it new.
the iac valve controls the idle and start up too i believe but that can be taken out and cleaned with brake cleaner.
same with the egr take it off the manifold and see if its plugged with carbon and not working right
good luck

WagoneerXJ
05-18-2010, 02:21 PM
Never seen TBI on a ford truck before

mus-Tard
05-18-2010, 06:52 PM
Never seen TBI on a ford truck before

thats what l was thinking.




but check your IAC and clean that out. also fuel filters.
if that line you disconected was right behind the first cat then that was you AIR injection to feed your second (reduction) cat.

that is not needed. mine is disconected.

your AIR pump is also known as a 'smog pump' and its not uncomon to take that off as it draws hp from your engine.

regulate34
05-18-2010, 08:54 PM
if your fuel pump primeing?
i have the same kind of issue with my 96
it turns out their is a check valve in the pump and it is desinged to allow the pressue to stay their after the pump is done primeing
check your fuel pressure and after the 2second prime make sure you pressure stays up

4skin
05-18-2010, 11:52 PM
:confused0006: did you disconect battery before wellding:dontknow: