1989 Bronco 5.8 starting

[captsb890]

My 89 used to start--without touching the pedal, fast and idle about 1500 until coolant warmed up and the drop to idle around 750----normal
But now it doesn't do that. I changed the coolant sensor, new idle valve (Motor craft) ignition control module,--TPS, Now I have to tap the pedal to get it to idle as start up it drops to around 4-5 hundred rpm.
I put an OBD 1 on it and it didn't show anything except thermactor left side---I don't think that has anything to do with it as it all worked fine until I had the transmission overhauled-- It worked even then so I don't think that had anything to do with it as they put a new throttle cable in----it worked but all of a sudden now it doesn't have that great start up like it used to.
What could it be-? I don't want to adjust the throttle plate idle, as it would give me a higher idle. I checked for vacuum leaks as it seemed to need more air. Couldn't find any vacuum leaks, I disconnected the battery , negative, as maybe the computer needed be be re-set----didn't help. New fuel pump--had 35psi steady---even tried to do the ignition twice before start--thinking maybe not getting enough fuel--no help ?
Is there maybe an adjustment at the pedal-?? maybe coolant sensor ,even new, is bad-? Once it starts it runs great--when hot fires right up. I'm perplexed--! Sam

 

[joserios1970]

My 89 used to start--without touching the pedal, fast and idle about 1500 until coolant warmed up and the drop to idle around 750----normal
But now it doesn't do that. I changed the coolant sensor, new idle valve (Motor craft) ignition control module,--TPS, Now I have to tap the pedal to get it to idle as start up it drops to around 4-5 hundred rpm.
I put an OBD 1 on it and it didn't show anything except thermactor left side---I don't think that has anything to do with it as it all worked fine until I had the transmission overhauled-- It worked even then so I don't think that had anything to do with it as they put a new throttle cable in----it worked but all of a sudden now it doesn't have that great start up like it used to.
What could it be-? I don't want to adjust the throttle plate idle, as it would give me a higher idle. I checked for vacuum leaks as it seemed to need more air. Couldn't find any vacuum leaks, I disconnected the battery , negative, as maybe the computer needed be be re-set----didn't help. New fuel pump--had 35psi steady---even tried to do the ignition twice before start--thinking maybe not getting enough fuel--no help ?
Is there maybe an adjustment at the pedal-?? maybe coolant sensor ,even new, is bad-? Once it starts it runs great--when hot fires right up. I'm perplexed--! Sam

I had the same problem.whit mi 90 bronco .I did replace almost same parts as you did .. untill.i pull out the distributior I found out the shaft has been whit lots of play .I did replace the distributior and now it's super terrific .good

 

[captsb890]

I had the same problem.whit mi 90 bronco .I did replace almost same parts as you did .. untill.i pull out the distributior I found out the shaft has been whit lots of play .I did replace the distributior and now it's super terrific .good

Thanks for that---With 202,000 miles ,I think I'll just put a new 351 in there---Been told a valve job and this and that---Would also increase the resale value!

 

[Tiha]

what happens to your fuel pressure when you shut the truck off and let it sit?

If it drops there could be bad fuel pressure regulator, check ball on fuel pump, or leaky injector. All of which make it harder to start after sitting.

 

[captsb890]

what happens to your fuel pressure when you shut the truck off and let it sit?

If it drops there could be bad fuel pressure regulator, check ball on fuel pump, or leaky injector. All of which make it harder to start after sitting.

Thanks--The pump puts out 35---i think my old pump put out 40--it had a bad check valve--starting issues are different--not as fast but, still within the book 5seconds--used to start as soon as I touched the key!---put new regulator in--think the old one actually, was ok.-

 

[L\Bronco]

My 89 used to start--without touching the pedal, fast and idle about 1500 until coolant warmed up and the drop to idle around 750----normal
But now it doesn't do that. I changed the coolant sensor, new idle valve (Motor craft) ignition control module,--TPS, Now I have to tap the pedal to get it to idle as start up it drops to around 4-5 hundred rpm.
I put an OBD 1 on it and it didn't show anything except thermactor left side---I don't think that has anything to do with it as it all worked fine until I had the transmission overhauled-- It worked even then so I don't think that had anything to do with it as they put a new throttle cable in----it worked but all of a sudden now it doesn't have that great start up like it used to.
What could it be-? I don't want to adjust the throttle plate idle, as it would give me a higher idle. I checked for vacuum leaks as it seemed to need more air. Couldn't find any vacuum leaks, I disconnected the battery , negative, as maybe the computer needed be be re-set----didn't help. New fuel pump--had 35psi steady---even tried to do the ignition twice before start--thinking maybe not getting enough fuel--no help ?
Is there maybe an adjustment at the pedal-?? maybe coolant sensor ,even new, is bad-? Once it starts it runs great--when hot fires right up. I'm perplexed--! Sam

Hey Captsb890
As Tiha said, put your pressure gauge on and cycle the key a couple times to get to full fuel pressure, then see how long it takes to leak down. I think the spec is around 15psi in 30 seconds (Don't quote me on that one, my memory isn't as good as it used to be) It sounds like a possible leaking injector or 2. It will cause one or more cylinders to "flood" on startup after it sits. An injector will usually leak slowly, so it takes a while to cause the concern. often overnight.
If it doesn't drop too much, then you might try doing a KOER (key on engine running test) with your code reader.
If the throttle body gets too much sludge buildup behind the throttle plates, it will act like the idle is too low, and it often only shows up on cold starts in its early stages. This test actually runs the idle up and down to verify that its in range.
Good luck
Cheers

 

[captsb890]

Hey Captsb890
As Tiha said, put your pressure gauge on and cycle the key a couple times to get to full fuel pressure, then see how long it takes to leak down. I think the spec is around 15psi in 30 seconds (Don't quote me on that one, my memory isn't as good as it used to be) It sounds like a possible leaking injector or 2. It will cause one or more cylinders to "flood" on startup after it sits. An injector will usually leak slowly, so it takes a while to cause the concern. often overnight.
If it doesn't drop too much, then you might try doing a KOER (key on engine running test) with your code reader.
If the throttle body gets too much sludge buildup behind the throttle plates, it will act like the idle is too low, and it often only shows up on cold starts in its early stages. This test actually runs the idle up and down to verify that its in range.
Good luck
Cheers

Thank you---I'll do some checking!

 

[L\Bronco]

Thank you---I'll do some checking!

Let us know how it goes!

 

[captsb890]

what happens to your fuel pressure when you shut the truck off and let it sit?

If it drops there could be bad fuel pressure regulator, check ball on fuel pump, or leaky injector. All of which make it harder to start after sitting.

Ater keying it twice it reads 40 psi---takes a long time to slowly drop--to about 35 ---then sitting for a while slowly goes down

 

[Motech]

Ater keying it twice it reads 40 psi---takes a long time to slowly drop--to about 35 ---then sitting for a while slowly goes down

That's a fine result.

For grins, try putting your old Idle Air Bypass Valve back on. I've had many, many aftermarket IAC valves not work as well as the old ones they replaced, including Motorcraft brand (which also is aftermarket). It's gotten so if I test and confirm the IAC is bad, I'll swap out with one of the old factory ones I've got laying around and get better results than the new aftermarket junk.

Also, TPS signal can get a little muddy at closed throttle and give off this exact symptom, especially if the throttle body has been cleaned with heavy chemical spray instead of wiping with a cloth moistened with carb cleaner. If that is the case, a little tweak on the throttle stop bolt... (will you let me write bolt here as that other "s" word so commonly used for small, threaded fasteners is just too risky for we sheltered Bronco wrenches to be exposed to FFS) Anyway, opening up your throttle blades a little might get past the corrupted closed-throttle voltage and bring your startups back to sweetness.