When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hi all.... First time poster, but have researched and used the information on this board extensively since I got by bronco.
Here's my problem
Every time the truck sits for more that an hour it takes 2-4 trys to get it started. I hear the pump come on and pressure up the system but it either sputters and dies or wont fire at all the first couple of times. The funny thing is that it seems to start better the colder it is outside. It has done this since I got it with 75K miles and it now has 130K. I have done the obvious and replaced the following: plugs, distributor cap, fuel filter, fuel pressure regulator...all to no avail. I decided to pull the codes before I keep wasting money, and see if you all could help. Here is what I got:
I have the sheet that defines the codes and they seem to point to the MAP or Knock sensor. Am I looking in the right direction, could this cause it to start hard? Other than this annoyance the truck runs great. Thanks in advance for any help!
'91 Bronco custom all Stock
4.9L EFI
Mazda 5 speed
31" Yokohama's
130K miles
Part of your problem is that you're reading the codes wrong. You computer uses 3-digit codes. Look at the definitions for 521, 181, & 556 (this link takes you to the instructions & a short list, but it has another link to my full list). Put a fuel pressure gauge on your fuel rail and see what it is when it's sputtering.
Thanks for setting me straight Steve. I found the definitions of those codes. Am going to try to get my hands on a fuel pressure tester tonight. Here's another question, I had to replace the gas tank (old one rusted through) a while back and it came off a '96 Bronco from a boneyard in Texas....with a fuel pump already in it. I didn't used that pump at the time, but if I do find that my problem in fuel pump related can I use the one from the '96. They cut the wiring harness when they pulled the tank off the donor vehicle.
Steve, I went to your link above and clicked on you link to the full list of code and read the following:
---------
KOEO
Continuous memory codes will be separated by a code 11. (92 and later models will have a 3 digit code and will flash the CHECK ENGINE light.)
KOER
(92 and later models will have a 3 digit code and will flash the CHECK ENGINE light) After repairs have been made, clear codes, run and recheck.
------
So does this mean I have two or three digit codes? My bronco is a 1991. Are data trouble codes and continous memory codes always the same lenght? Thanks
KU, my book says that 91 was a transition year for the 2/3 digit codes, so yours might use either one (depending upon the date of mfg). I suspect it's 2 digit, because the 3 digit code definitions make no sense for a hard start.
I would look at the IAC (idle air control). It may be plugged with carbon, as may the throttle body blade area. Clean them both, and see if it helps. If not, try cleaning the MAF sensor next. (Do a search for the procedures, there's bunches.)
Since it starts good when cold, it may be a faulty or corroded temperature sensor. Although the codes don't point to that......
Thanks guys, I am going to use the two digit codes and start my diagnosis from there. Will take the lonerangers advice and clean the IAC and throttle body, Im sure they have never been off before. Is a MAP/BAP sensor a servicable item or is it better to replace it? And what exactly does it do?
MAP sensor is not servicable, although it is testable. Do a search for "test MAP sensor" and you'll find the procedure; it gives its output as a frequency so you'll need a meter that picks up frequencies.