Idle & Hesitation Issues
Idle & Hesitation Issues I need some help with my '02 5.3 swap into my '67 Bronco. On start up the idle jumps way up, almost to 3K and the slowly comes down. Even when it settles at high idle when revved it comes down slowly. Also when I am driving it drives normal when under about 30% throttle, but whenever I depress the throttle further it has a huge hesitation and doesn't accelerate any faster. The MAF is brand new and I cleaned it just to be sure, my O2s are brand new but have been causing issues (wouldn't explain the idle), I have sprayed carb cleaner everywhere and cannot find a leak. If I unplug my TPS sensor the idle drops down to normal & when revved it drops back down quickly like it should. Also when I unplug the IAC nothing happens? Any suggestions on what the issue is? The only codes I am pulling are P0507 (high idle), P0134 & P0154 (O2 inactivity). Obviously I am replacing the O2s, but what about the idleing and hesitation/ no-go issues?
Try hooking up the O2's. That may alleviate your problem. Once you've got the o2 going it's one less thing that could potentially cause your problem. Are you using DBW or Cable TB? If it's cable type, then ensure that your TPS is adjusted correctly.
Thanks for replying. I have always had O2s hooked and they never threw a code until now, but the motor has always done this since swapped. It is a cable TB and I just got a hold of spare TPS & IAC sensors. My understanding is that you only need to adjust the TPS on an aftermarket TB? I will try replacing it in a couple hours because I have a spare.
was the tune messed with. If so, return all tables to stock and start from there. Maake sure heads grounds are good and make sure the alt charging, low batt will send idle and fuel thru the roof.
The tune is all stock, just modified for no emmisions. I have not performed a vacuum test per se, but I have sprayed every square inch of the motor with carb cleaner and got no response anywhere.
Tonight I put in new O2s and that took care of the O2 code of course. I pulled a functional TB w/ TPS & IAC sensors off of my buddies motor and swapped it in and it made no difference to the idle issue. I also put a can of Seafoam in the tank and ran it around some and the hesitation lessened but it is still prevelant. I think the hesitation issue may be a mixture of dirty injectors & what ever is causing the idleing problem (maybe causing a lean condition).
The odd part is that if I am cruising at 60MPH & 1700 RPM and roll into the throttle the vehicle actually seems to slow down and as I ease out of the throttle it starts accelerating again (change in speed is very mild, but noticeable). WTF?
Tonight I put in new O2s and that took care of the O2 code of course. I pulled a functional TB w/ TPS & IAC sensors off of my buddies motor and swapped it in and it made no difference to the idle issue. I also put a can of Seafoam in the tank and ran it around some and the hesitation lessened but it is still prevelant. I think the hesitation issue may be a mixture of dirty injectors & what ever is causing the idleing problem (maybe causing a lean condition).
The odd part is that if I am cruising at 60MPH & 1700 RPM and roll into the throttle the vehicle actually seems to slow down and as I ease out of the throttle it starts accelerating again (change in speed is very mild, but noticeable). WTF?
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Have you had a fuel pressure gauge on it that you could see while driving? The last thing you described sounds like low fuel pressure so as you get on it at speed it actually leans out past the lean burn limit and the car noses over..picking back up when you get off the throttle. How is the fuel system set up?
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Verdad Gallardo Have you had a fuel pressure gauge on it that you could see while driving? The last thing you described sounds like low fuel pressure so as you get on it at speed it actually leans out past the lean burn limit and the car noses over..picking back up when you get off the throttle. How is the fuel system set up?
I have seen people talk about using those MSD pumps but I never have. They are only rated at running around 45psi if I recall correctly. You definitely need to beg, borrow, or steel a fuel pressure gauge you can put on the rail with enough lead that you can slide it under your windshield wipers and watch it as you drive. This could be causing a lot of your issues. Obviously if you don't have enough fuel and you keep getting on it, you are going to have another issue - needing another 5.3.
added: even a fuel pressure tester from autozone or a buddy would be fine to just screw onto the shrader valve and place where you can see it for testing. Don't really need to build one into the vehicle if you dont want. Although, I think a -4an premade line, -4an to 1/8 female NPT and a small 0-100 psi gauge would be all thats needed and 5 minutes to install if you wanted a permanent one...not a bad idea IMHO
added: even a fuel pressure tester from autozone or a buddy would be fine to just screw onto the shrader valve and place where you can see it for testing. Don't really need to build one into the vehicle if you dont want. Although, I think a -4an premade line, -4an to 1/8 female NPT and a small 0-100 psi gauge would be all thats needed and 5 minutes to install if you wanted a permanent one...not a bad idea IMHO
I have seen people talk about using those MSD pumps but I never have. They are only rated at running around 45psi if I recall correctly. You definitely need to beg, borrow, or steel a fuel pressure gauge you can put on the rail with enough lead that you can slide it under your windshield wipers and watch it as you drive. This could be causing a lot of your issues. Obviously if you don't have enough fuel and you keep getting on it, you are going to have another issue - needing another 5.3.
added: even a fuel pressure tester from autozone or a buddy would be fine to just screw onto the shrader valve and place where you can see it for testing. Don't really need to build one into the vehicle if you dont want. Although, I think a -4an premade line, -4an to 1/8 female NPT and a small 0-100 psi gauge would be all thats needed and 5 minutes to install if you wanted a permanent one...not a bad idea IMHO
added: even a fuel pressure tester from autozone or a buddy would be fine to just screw onto the shrader valve and place where you can see it for testing. Don't really need to build one into the vehicle if you dont want. Although, I think a -4an premade line, -4an to 1/8 female NPT and a small 0-100 psi gauge would be all thats needed and 5 minutes to install if you wanted a permanent one...not a bad idea IMHO
EDIT: My fuel pump is actually a Summit branded pump good for 85PSI and 500HP. http://www.summitracing.com/parts/SUM-G3138/
Last edited by madmaro00; Aug 25, 2009 at 10:08 AM.
I haven't had any issues with the truck FPRs but anything can go bad. I have had lots of issues over the years with any cheaper fuel pumps though. Had more of the offbrand and Airtex/ Autozone etc pumps go bad or be bad right off the bat than I can count. Hard to beat a good Delphi/ AC-Delco or Walbro pump. Get a gauge on it just to rule that out. If the pressure is low and you suggest the regulator, cap off or block the return and see what the fuel pressure does, this will point your problem to either the regulator (pressure goes up) or the pump (pressure doesnt really change)
I drove it to the dealership after work (about 50 miles) and on the way the problem started clearing up more. By the time I got to the dealer it was non-existent. The dealer drove it and gave it the full check-up with the Tech2 to give me the warm fuzzies and the said everything is flawless. I'm so pumped, time to go turn and burn in the dunes! Thanks guys, Justin.
