ComancheKid45 Posted September 30, 2011 Posted September 30, 2011 Alright, well I'm back again with another puzzle for you guys. this is my 88 4.0 AW4 4x4. The following parts have just been installed in the past 2 months... Crank sensor Wires/Cap and Rotor Fuel Pump Fuel Pressure Regulator Knock sensor (should be irrelivent) Coolant Sensor in the block MAP Sensor EGR Valve will be here tomorrow Alrighty, well since ive installed the new fuel pump alittle over 2 weeks ago the truck has gone from 2-3 seconds to startup up to 6-9 seconds, ok ive delt with it well, now its really throwing a fit to start, once i fire it up (2-3 tries) and its still cold itll idle itll run fine. Once it hits operating temp. it then slowly begins to fall on its face, starting at feeling sluggish all the way to backfiring through the TB and "misfiring"/idling like garbage... The Oxygen sensor and spark plugs were just replaced back in Janruary but after an inspection of the plugs this evening the cylinders are definently loading up with fuel and the oil has a faint scent of gasoline also (oil change will be performed asap). The truck is not overheating on the gauge. I'm going to throw a new o2 sensor in it tomorrow as well as my new EGR valve, but otherwise i don't know what else it could be. Thanks for any advice as always!
big66440 Posted September 30, 2011 Posted September 30, 2011 Hows the flow in the fuel return lines? cat plugged up? defective replacement part?
ComancheKid45 Posted September 30, 2011 Author Posted September 30, 2011 Cat is hollowed ( :roll: ) Return lines had fuel when regulator was installed as well as the pump. symptoms really escalated after new fuel pump was installed but otherwise can't think 1 of the other parts are faulty :dunno:
mvusse Posted September 30, 2011 Posted September 30, 2011 Fuel pump or filter. You did replace the fuel pump sock when you replaced the pump, right?
ComancheKid45 Posted September 30, 2011 Author Posted September 30, 2011 Sock "seemed" clean and was cleaned up and re installed, filter has been on a few years, will change that as well. Engine is definetly getting fuel, from what I gather its just getting too much. I'm thinking about going back to the other Fuel pump, afterall it was running great before i swapped that out, only swapped it with a new 1 since i had 2 remove the assembly to change the O Ring.
mvusse Posted September 30, 2011 Posted September 30, 2011 If it's not getting enough, it could be pump, sock, filter, clogged line or regulator. If it's getting too much it's the regulator or ECM. The pump is supposed to pump more than the engine needs. The pressure is bled off by the regulator and returned to the tank via the return line. Also, the sock is supposed to be replaced whenever a new pump is installed, and failure to do this voids the warranty on a new pump.
JeffN Posted September 30, 2011 Posted September 30, 2011 pressure should be 31 lbs at idle and 39 at idle with the vacuum line off the regulator and it should hold pressure when you shut the engine off
ComancheKid45 Posted October 2, 2011 Author Posted October 2, 2011 Well i believe i can put a period on this 1. Or atleast what the hard starting issue was Upon removing the fuel pump and sender from the tank i noticed the lower hose clamp on the pump itself was loose, thuss allowing fuel pressure to leak back into the tank and not sustain in the line, after tightining that up and re installation as well as many other parts I did get a small stumble or 2 during about 40 miles of driving but overall I believe i got it. :D
jpnjim Posted October 2, 2011 Posted October 2, 2011 :cheers: Glad you got it. Renix's are great when they work, but can be a huge PITA to diagnose sometimes. (I've been chasing a part throttle stumble in my 88' for a while now).
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