[Donvitto1290]

So I have some issues. I have a 1991 5.0 EB. Starting the project up as it is getting colder outside. Bought it non running, finally got it to start up with some part replacements. But now it’s seeking rpm from 700-1500 rpm sparatically before dropping below 500 and dying. Here is a list of parts replaced so far... yes it’s a long list...

Fuel Pump
Fuel Relay
Fuel filter
Fuel regulator
TPS
IACV
Distributor (including cap, rotor, ICM)
Ignition coil
Starter
Alternator
Starter relay
Ignition switch
Ignition actuator
Lock cylinder

tomorrow... MAP
any help would be amazing

 

[BroncMom]

Jumping rpm could be vacuum. I don't see new lines on your list.

 

[BroncMom]

Jumping rpm could be vacuum. I don't see new lines on your list.

 

[rpeters549]

A hunting idle is often a vacuum leak.

Sent from my Pixel 3 XL using Tapatalk

 

[jermil01]

Hi @Donvitto1290 , welcome to FSB..while it could very well be vacuum related, before you go throwing any more parts at, have you checked for codes?? That will at least give us a base line of what we're working with. Over time as the EEC's age in these rigs they do start to go bad, so that is something to potentially be aware of.

Was going to suggest checking fuel pressure as well, but I see you pretty much replaced the entire system.

For reference, here's a great thread that covers replacing all the vacuum lines. Good luck.

Replace Plastic Vacuum Hoses with Rubber

This should cover most 87-96 V8s (302\351); for the I6s (300)s the solenoids are in the same general area, as well as the valves. You can use this article as a basis to replace yours, just keep in mind it will be slightly different. Parts you'll need: All available from a local autoparts...

www.fullsizebronco.com

 

[Donvitto1290]

Jermil thanks for the input on vacuum lines with the link. It’s not loading on my phone so I’ll hope on the laptop and see if it works on there. I was only getting a 62 tps code but the it’s the first time I’ve ever had to use a jumper wire to get codes on leer vehicles I am used to mopar’s turn the key 5 times.
Fuel pressure in the rails prior to replacing everything was 40 when turning key to on. With engine on it dropped to 30 so I just replaced everything so I wouldn’t have to. All the parts I have been replacing were original so they would’ve went at some point. It’s a project after all.
It’s a Cali rust free but not dust or heat damage free especially in the Central Valley. So I will start looking a vacuum lines after my paycheck I’ve already spent enough this paycheck lol

 

[Siggy89]

Here's my .02 based on a similar problem I had recently.

Since you've replaced the bulk of the fuel system I think it's an air issue. I'd replace the EGR Valve and EGR solenoid first. If that doesn't work my next step would be to replace the EEC (computer) that runs the ratios. The truck is 30 years young.

Similar situation happened on my 1992. EGR valve and solenoid replacement fixed it for awhile, but once I swapped in a rebuilt computer everything was gravy. But look into the valve and solenoid first because if they're no good, it won't matter if you replace the computer.

 

[BroncMom]

Not that I'm any kind of a pro here but wouldn't the cheapest alternative be replacing the lines first since they're original and likely desert rotted? After all it is a project and they likely definitely need it 🤷 and vacuum line is pretty cheap...

 

[TomR]

Looks as if water pump, power steering pump, radiator and master cylinder about all you haven’t replaced... not critical assessment as you have made a big investment in this Bronco. Which I appreciate. Guess my point is if your long term plan is keeping the Bronco then money well spent. Run a compression test to see the overall condition of the motor. You bought it not running, so stop, assess what you have.

 

[Rob_64-365]

I had bought my bronco barely running, and like you replaced everything I could buy EFI related. It ran much better, but still had a hunting idle. I pulled off vacuum hoses at the manifold one at a time, and plugged the steel post that the vacuum hose plugged on to & found that when I pulled off the vacuum line to the cruise control, it settled the idle... my cruise control module had rusted thru, and that was my vacuum leak.
Additionally, after being annoyed enough times trying to count flashes to get my codes, I bought a $29 OBD1 code reader at autozone, and found several items throwing codes, which once i corrected them, it really started running as it should. I have just gone down this same road you are on, go read my build/restoration thread, I tried to include as much information as I could as to how I found the problems and corrected them.

 

[Jeffs 96]

So I have some issues. I have a 1991 5.0 EB. Starting the project up as it is getting colder outside. Bought it non running, finally got it to start up with some part replacements. But now it’s seeking rpm from 700-1500 rpm sparatically before dropping below 500 and dying. Here is a list of parts replaced so far... yes it’s a long list...

Fuel Pump
Fuel Relay
Fuel filter
Fuel regulator
TPS
IACV
Distributor (including cap, rotor, ICM)
Ignition coil
Starter
Alternator
Starter relay
Ignition switch
Ignition actuator
Lock cylinder

tomorrow... MAP
any help would be amazing

I had a similar issue on an '88 w/ 5.0L. I took off the throttle body and cleaned it with carb cleaner. It was gunked up with carbon in the internal emission passages. Also had to do the same to an '89 5.0 Mustang and my '96 Bronco. Maybe give it a try ... could be a cheap fix and can be done in less than an hour.