Broco II "bucks and jerks"

chrislang · 04-02-2012, 10:16 AM

Newbe here with 86 2.9l 5 speed.

I know you guys must have had this discussion come up, but I searched and cannot seem to find an answer.
Issue: Starts up and idles fine. When taking off it is fine, if you rev the engine up on take off. Idles fine, and will rev up fine parked in neutral. It stumbles and jerks violently upon acceleration between shifts. I just bought this, because it is in such good shape. No rust, immaculate interior.
The guy I bought it off of has tested virtually ALL of the sensors, changed both fuel pumps, drained the tank, replaced the computer, new plugs and wires.... NO CHANGE...

Temp. does not seem to matter, IE: does not start this acting up when hot, it can happen anytime. Vacuum issue,(can't find any) Timing? (set 10deg. BTDC)..Cold spark? Maybe I need to use the Motorcraft 42Cs? (not sure whats in it now)

The motor was swithed out to one with a lot less miles. The guy I bought it from wasn't sure of the year although he said it was newer.

Could it be the motor mounts?? I have a truck that acted like that when it needed motor mounts.(Runs fine in 5th gear when your accelerating) Seems to happen most when you are letting off the accelerator, then resuming acceleration.

I know you guys must have discussed this ad nauseam in the past. If so, please point me to the link.

I really like the BII and am determined to find the issue. I hope you guys can help. Any and all comments will be appreciated!!

Thanks in advance!

Chris

85_Ranger4x4 · 04-02-2012, 11:04 AM

It is a Bronco, did you not see the bucking horse badge?

You might install a vacuum gauge in it and see what it is doing realtime as you drive it.

Probably a nonissue but you did unplug the dizzy when you set timing right?

chrislang · 04-02-2012, 12:33 PM

Quote:

Probably a nonissue but you did unplug the dizzy when you set timing right?

By dizzy, do you mean the SPOUT plug? I did indeed unplug it. Does that stand for SPARK-OUT? It is not one of those typical TFI things about getting hot, then shutting off. As long as I am accelerating it seems to do ok. But in between shifts, it bucks when pressing the throttle as you release the clutch.

Thank you all for any info, as I am at a loss of ideas.......

Danni84 · 04-02-2012, 01:34 PM

"Seems to happen most when you are letting off the accelerator, then resuming acceleration"
I dont know if the 2.9 has it or not but my 2.8 did that and the EGR valve was stuck closed from carbon build up. Finally got it diagnosed after the 3rd mechanic looked at it. EGR valve and timing had it running well again.

85_Ranger4x4 · 04-02-2012, 01:41 PM

Yeah, dizzy = distributor = spout plug (implied, sorry)

chrislang · 04-02-2012, 01:54 PM

Quote:

"Seems to happen most when you are letting off the accelerator, then resuming acceleration"
I dont know if the 2.9 has it or not but my 2.8 did that and the EGR valve was stuck closed from carbon build up. Finally got it diagnosed after the 3rd mechanic looked at it. EGR valve and timing had it running well again.

Thanks Dannie84!
I'll try that this evening or tomorrow. It can't hurt!

tw205 · 04-04-2012, 03:59 PM

Sounds like a faulty throttle position sensor

**shane96ranger** · 04-04-2012, 04:33 PM

Have you checked for play in the distributor shaft?

tdjar · 04-25-2012, 12:45 PM

I have an '86 as well and it does the same thing except it happens when I try to maintain a constant speed. Doesn't matter what gear I'm in or what speed I'm going. I haven't been able to get at this yet 'cause the input bearing went in the tranny , it is going back in this weekend, then it will be diagnosis time. I will post what I find and hopefully we can figure this out

04-02-2012, 10:16 AM	#1
chrislang New Member Join Date: Apr 2012 Year: 1986 Make: Ford Model: Bronco II Posts: 3 Rep Power: 0 iTrader: (0)	Broco II "bucks and jerks" Newbe here with 86 2.9l 5 speed. I know you guys must have had this discussion come up, but I searched and cannot seem to find an answer. Issue: Starts up and idles fine. When taking off it is fine, if you rev the engine up on take off. Idles fine, and will rev up fine parked in neutral. It stumbles and jerks violently upon acceleration between shifts. I just bought this, because it is in such good shape. No rust, immaculate interior. The guy I bought it off of has tested virtually ALL of the sensors, changed both fuel pumps, drained the tank, replaced the computer, new plugs and wires.... NO CHANGE... Temp. does not seem to matter, IE: does not start this acting up when hot, it can happen anytime. Vacuum issue,(can't find any) Timing? (set 10deg. BTDC)..Cold spark? Maybe I need to use the Motorcraft 42Cs? (not sure whats in it now) The motor was swithed out to one with a lot less miles. The guy I bought it from wasn't sure of the year although he said it was newer. Could it be the motor mounts?? I have a truck that acted like that when it needed motor mounts.(Runs fine in 5th gear when your accelerating) Seems to happen most when you are letting off the accelerator, then resuming acceleration. I know you guys must have discussed this ad nauseam in the past. If so, please point me to the link. I really like the BII and am determined to find the issue. I hope you guys can help. Any and all comments will be appreciated!! Thanks in advance! Chris
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04-02-2012, 11:04 AM	#2
85_Ranger4x4 Member Join Date: Aug 2007 Location: Between Omaha & Des Moines Year: 1985 Make: Ford Model: Ranger Engine: 5.0 Class: 4x4 Used For: A weapon of massive consumption. Posts: 11,267 Rep Power: 52 iTrader: (0)	It is a Bronco, did you not see the bucking horse badge? You might install a vacuum gauge in it and see what it is doing realtime as you drive it. Probably a nonissue but you did unplug the dizzy when you set timing right? __________________ 1985 Ford Ranger Custom, 4x4, PA 3" BL, 5.0 HO wannabe, C5 Transmixer, 31 spline T/L 8.8 w/ disc brakes. Build Thread My Ranger is not old; no one would call her old. She has a bluff bow, lovely lines. She's a fine truck: weatherly, stiff and fast... very fast, if she's well handled. No, she's not old; she's in her prime.
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04-02-2012, 01:34 PM	#4
Danni84 New Member Join Date: Feb 2012 Location: KS Year: 1984, 1988 Make: Ford Model: Ranger, Bronco II Engine: 2.8l 104k miles & 2.9l 245k miles Class: 4X4 Used For: Work in Progress Posts: 23 Rep Power: 0 iTrader: (0)	"Seems to happen most when you are letting off the accelerator, then resuming acceleration" I dont know if the 2.9 has it or not but my 2.8 did that and the EGR valve was stuck closed from carbon build up. Finally got it diagnosed after the 3rd mechanic looked at it. EGR valve and timing had it running well again.
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04-02-2012, 01:41 PM	#5
85_Ranger4x4 Member Join Date: Aug 2007 Location: Between Omaha & Des Moines Year: 1985 Make: Ford Model: Ranger Engine: 5.0 Class: 4x4 Used For: A weapon of massive consumption. Posts: 11,267 Rep Power: 52 iTrader: (0)	Yeah, dizzy = distributor = spout plug (implied, sorry) __________________ 1985 Ford Ranger Custom, 4x4, PA 3" BL, 5.0 HO wannabe, C5 Transmixer, 31 spline T/L 8.8 w/ disc brakes. Build Thread My Ranger is not old; no one would call her old. She has a bluff bow, lovely lines. She's a fine truck: weatherly, stiff and fast... very fast, if she's well handled. No, she's not old; she's in her prime.
	Tweet

04-04-2012, 03:59 PM	#7
tw205 Junior Member Join Date: Jan 2011 Location: Angola Indiana Year: 1985/1988/2000 Make: Ford Model: Bronco II/Mustang LX/F-250 Superduty Engine: None/5.0/6.8 Class: 4x4 Used For: An excuse to drink in the garage Posts: 34 Rep Power: 5 iTrader: (0)	Sounds like a faulty throttle position sensor
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04-25-2012, 12:45 PM	#9
tdjar New Member Join Date: Oct 2011 Year: 1986 Make: Ford Model: Bronco II Posts: 2 Rep Power: 0 iTrader: (0)	I have an '86 as well and it does the same thing except it happens when I try to maintain a constant speed. Doesn't matter what gear I'm in or what speed I'm going. I haven't been able to get at this yet 'cause the input bearing went in the tranny , it is going back in this weekend, then it will be diagnosis time. I will post what I find and hopefully we can figure this out
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