Bronco Forum - Full Size Ford Bronco Forum banner
1 - 11 of 11 Posts

·
Registered
90 Bronco, 4.9 inline, 5 speed mazda. skyjacker level coils + 4 shocks on 33x12.50 A/T on 15x10
Joined
·
33 Posts
Discussion Starter · #1 ·
Hello y'all
My 1990 Bronco 4.9 has been giving me hell. I decided to replace my whole ignition system. New plugs, wires, distributor and coil. My plugs are motocraft copper cores and my timing is set to 12°. Before I did this my truck ran well, but I felt replacing 30 year old parts would be good of me since this is my daily. What ive run into is the truck now hard starts, has to crank much more than before and runs rough for about 5 to 10 seconds then smooths out. She also sounds like shes missing when I get above 1/2 throttle, like the distributor is wet. I'm at a total loss here and dont want to throw money at it chasing false alarms, any and all help is greatly appreciated. Thank yall!
 

·
Registered
1984, 300 L6, smogless, manual 3speed with overdrive.
Joined
·
2,318 Posts
First thing I’d do is double check the firing order to be sure your plugs are on the right firing order , then start messing with the dizzy a few degrees each way, when my to freshly built Fords (460 & 300) had a rough time starting I just kept moving the distributor till they found that sweet spot.
 

·
Registered
90 Bronco, 4.9 inline, 5 speed mazda. skyjacker level coils + 4 shocks on 33x12.50 A/T on 15x10
Joined
·
33 Posts
Discussion Starter · #4 ·
Thanks yall, I'll mess with the timing tmr. I pulled codes tonight and got 167, bad TPS it seems. Do my symptoms sound like a bad tps? Anymore idea would appreciated!
 

·
Super Moderator
Joined
·
5,168 Posts
IF adjusting the timing fixes it, you should check that your harmonic balancer hasn't slipped. If it has, the outer ring won't be lined up properly and even though it says it's at 12°, it won't actually be at 12°.
You can also check this by bringing the #1 piston to TDC (pull the #1 or #6 spark plug and look in the hole with a flashlight and turn the engine until the piston is at its highest point). Then, check your timing mark. It should be pointed at 0. If not, you need to replace your balancer ASAP.
 

·
Premium Member
If it is not a Bronco, it's just not worth driving.....
Joined
·
1,900 Posts
Make sure your vacuum lines are all good. Bad vacuum lines can rob you of power too....
 

·
Registered
1984, 300 L6, smogless, manual 3speed with overdrive.
Joined
·
2,318 Posts
IF adjusting the timing fixes it, you should check that your harmonic balancer hasn't slipped. If it has, the outer ring won't be lined up properly and even though it says it's at 12°, it won't actually be at 12°.
You can also check this by bringing the #1 piston to TDC (pull the #1 or #6 spark plug and look in the hole with a flashlight and turn the engine until the piston is at its highest point). Then, check your timing mark. It should be pointed at 0. If not, you need to replace your balancer ASAP.
We check tdc on #1 with a 36 inch 1/2 inch socket extension slip it in the hole spin the Jesus nut (Jesus that night and tight) and wait till it reaches max height.
 

·
Registered
Joined
·
142 Posts
Thanks yall, I'll mess with the timing tmr. I pulled codes tonight and got 167, bad TPS it seems. Do my symptoms sound like a bad tps? Anymore idea would appreciated!
Yes, the TPS is a variable resistor and it can get dead spots in it. It can make the truck do all sorts of bad things. I don't know how to check this on the 4.9 but typically you just need a voltmeter and you can have someone measure the voltage on the pins of the TPS as you rotate the TPS (or have someone slowly step on the gas pedal with the truck off as you measure it).
 

·
Registered
Joined
·
327 Posts
Thanks yall, I'll mess with the timing tmr. I pulled codes tonight and got 167, bad TPS it seems. Do my symptoms sound like a bad tps? Anymore idea would appreciated!
Yes, if the computer is throwing a code for a bad part then replace the part. These computers are simple so they only show what is failed.
 

·
Registered
90 Bronco, 4.9 inline, 5 speed mazda. skyjacker level coils + 4 shocks on 33x12.50 A/T on 15x10
Joined
·
33 Posts
Discussion Starter · #10 ·
Alright, I replaced the tps and it helped when on the throtttle but the idle is still bad. I bought a Haynes manual and it turns out ive not been removing the spout connector but the connector to the noise ballast. So tomorrow I will be going over the timing again and see how she runs. Thank y'all and hope for the best!
 

·
Super Moderator
Joined
·
29,093 Posts
Yo Nater,
Borrow or purchase a vacuum gauge and read this Vacuum Gauge Diagnosis @
1996 Bronco/F-Series
Similar to other EFI years.

One way to do a quick check is to grab a vacuum gauge. Some parts stores will loan you a gauge with refundable deposit.
The vacuum gauge should read between 15 and 22 in-Hg depending upon the engine condition and the altitude at which the test is performed. SUBTRACT ONE INCH FROM THE SPECIFIED READING FOR EVERY 1,000 FEET OF ELEVATION ABOVE SEA LEVEL.
The reading should be quite steady. .
When engine is rapidly accelerated (dotted needle), needle will drop to a low (not to zero) reading. When throttle is suddenly released, the needle will snap back up to a higher than normal figure.

When vacuum leaks are indicated, search out and correct the condition. Excess air leaking into the system will upset the fuel mixture and cause conditions such as rough idle, missing on acceleration, or burned valves. If the leak exists in an accessory unit, such as the power brake, the unit will not function correctly. Or Air Conditioning when in MAX mode may switch to Defrost.
Read more in my post #11 @ Help with dtc codes and idle
 
1 - 11 of 11 Posts
Top