Bronco Forum - Full Size Ford Bronco Forum banner

1 - 15 of 15 Posts

·
Registered
Joined
·
8 Posts
Discussion Starter #1
I own a 1989 bronco 4.9L inline 6 5speed. Lately the truck has been hard to start. If the truck is not driven for 3 or 4 days, it starts immediatly, otherwise it takes a few cranks and the idle will stumble initially. Also, the idle quality when running has deteriorated. Instead of a smooth idle, I get a rolling idle. For instance, when the truck is warmed up, the idle will drop to almost stalling, then jump back up over 1000rpm and slowly settle back down to almost stalling over and over as if the computer is changing the timing. Another symptom I have is that if the truck is accidently stalled, upon restart, the starter seems to have a reluctance to turn the motor, just as if the timing were way to advanced. After letting it sit for a few seconds, it will start normal. Although its only an hunch, I feel it may be timing related. The things I have checked so far are replaced coolant temp sensor, and ISC valve. All standard maintenance has been done on this truck. Before I throw tons of money at the problem only to find it was something dumb and cheap, I'd like your input on what it could be.

Thanks in advance
Dave
 

·
CheeseBurger Milkshake!!
Joined
·
3,760 Posts
Try resetting the computer, also look for any possible vacuum leaks.

How long has it been since the O2 sensor has been replaced?

Good Luck!
 

·
Registered
Joined
·
8 Posts
Discussion Starter #4
forgot to mention I just changed the o2 sensor maybe 2 weeks ago hoping that would help. I checked for vacuum leaks and couldn't seem to find any, also replaced all the easy to get to hoses while I was there. I'll try resetting the computer, but I am pretty sure I tried that a few weeks ago.

As far as codes go I never noticed any check engines, but i have the scan tool, so I might as well check. The funny thing is I disconnected the knock sensor to see if it would have any effect and I never got a check engine. I'll give code checking a try.

Thanks
 

·
Registered
Joined
·
1,616 Posts
A couple possible problems here. 1 is that your egr valve is bad. 2 is that you could have a bad Idle Control Motor. My 300 is doing the samething you're describing...the "rolling idle". I'm going to replace my throttle body with the one I pulled off my 91 to see if that does anything. I sprayed some carb cleaner in the one on the truck now to clean it out......shop teacher said it would be ok for throttle bodies.......wrong! :mad: So I'm going to see if that does anything. I also have a stuck egr valve....
 

·
Registered
Joined
·
8 Posts
Discussion Starter #6
replaced the idle control motor, forgot to mention that too. I'll troubleshoot the throttlebody and egr valve.

Thanks
Dave
 

·
Registered
Joined
·
8 Posts
Discussion Starter #9
OK, well an update. I had a little bit of time this week and my replacement ECU arrived. I gave that a try. No good, but I did get a check engine, which I didn;t get before. I pulled the codes and it was 33 and 41. Lean condition and EGR stuck. I checked all the vacuum lines around the EGR and didnt come up with anything. I pulled the vacuum off the egr and noticed that I didn't really get any vacuum. Is this normal? I saw there was what seems to be a vacuum switch valve controlling it underneath the EGR. I pulled off the vacuum feed to that and no vacuum before the VSV as well. Should I be getting vacuum at that point? I also noticed what looks like a sensor bolted onto the actual EGR valve. I have no cue what this is.

Listed under the codes to check are:

33 EGR not opening Clogged or bad EGR, bad EVP/PFE sensor, and even a sluggish O2 can set this.

O2 sensor is new. I am at school and my manual is at home. I do not know how to trouble shoot the EGR and evp/pfe sensor

41 O2 low (lean) Vachum leak, EGR stuck open,bad MAP sensor, bad O2, clogged fuel filter,weak fuel pump

Fuel filter and pump are new. Another reference to EGR which puts that at the top of my troubleshoot list. MAP: could be, don't know how to troubleshoot that either, although, wouldn't the computer have trouble calculating mixture all the time though, not just at idle? I'll save that for when I am out of ideas.
 

·
OUT OF BUSINESS / M.I.A.
Joined
·
10,873 Posts
check fuel pressure
Remove EGR and make sure it staying closed at idle.
Put a vacuum gauge T'ed in the EGR vacuum line and test drive the truck. Check to see when and how much vacuum it has.
Check the PCV valve it can cause issues too
 

·
Registered
Joined
·
8 Posts
Discussion Starter #13
I'll try checking that out, the strange part of it seems the vacuum feed to the solenoid doesn't even get vacuum. Its a crazy routing too, I see it came off the intake into the charcoal canister and a bunch of other hard to reach places before it gets to the egr. I'll check it out though.

Thanks
 

·
Registered
Joined
·
8 Posts
Discussion Starter #14
Resolved! Fireguy50, you hit it. Bad fuel pressure regulator. The diaphram ruptured. Thanks for all your help, truck is running like new with 160,xxx on it!
 
1 - 15 of 15 Posts
Top