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1985 Ford Mustang Lean/Timing issues

Tiny
FIXALLMAN_77808
  • MEMBER
  • 1985 FORD MUSTANG
  • V8
  • 2WD
  • AUTOMATIC
  • 175,635 MILES
Why is my timing when I checked it, advance to approx 28 degrees at about 2000 rpm, then retard to 12 by 3000rpm? I just purchased the car and noticed it will get weak under full throttle after about 2500 rpm and stop pulling by 4000. It's currently set at about 14 degrees at idle. The plugs say lean condition, and it seems to be thru out the rpm range. What should I look at first?
Sorry. Let me clearify. This is a 85 5.0 CFI intake, electrically controlled timing. Guessing this is a control issue. Thinking along the lines of o/2 sensor. I've checked my plugs after a short drive and after a long hard pull with emmediate shut down and check and have found the plugs to be showing lean condition. Little short on money after this purchase and am looking for help thru the net so as to work out a game plan of attack on this issue.
A lean condition from idle all the way thru red line seems to be the issue causing the computer to pull timing after 2000 rpm. I appreciate the ansmer to my question. Felt I needed a little clearification on my engine type. Sorry for the lack of info.
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Saturday, June 6th, 2009 AT 12:04 AM

14 Replies

Tiny
MIKE H R
  • MECHANIC
  • 3,094 POSTS
The timing should be 12 degrees at idle with the vacuum advance disconnected and the hose of the engine glugged. After the initial setting the advance should increase with the increase in engine speed. There could be a problem with the advance unit. Where it is loosing vacuum as the engine speed increases.
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Saturday, June 6th, 2009 AT 7:50 AM
Tiny
FIXALLMAN_77808
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  • 9 POSTS
I left some info out of my initial posting. This is an 85 5.0, CFI intake, electrically controlled advance. This lean condition exists from idle thru full throttle and appears to be coming from th O/2 sensor reading and causing timing to be pulled after 2000 RPM. Just need a direction to follow to get my game plan on.
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Sunday, June 7th, 2009 AT 6:32 PM
Tiny
MIKE H R
  • MECHANIC
  • 3,094 POSTS
Didconnect the battery and leave off for a few minutes, then reattach this could help and reset the computer so it picks up the correct settings.
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Saturday, June 13th, 2009 AT 1:45 PM
Tiny
FIXALLMAN_77808
  • MEMBER
  • 9 POSTS
Thank you for this answer, However I've had to do this several times with other repair issues in interior and it doesn't seem to help. Still getting a lean condition and miss. This miss seems to go away when I advance the timing beyond specs but it failed emmissions. Had to move it back to 12 before it would pass. So still looking for a possible solution.
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Saturday, June 13th, 2009 AT 3:38 PM
Tiny
MIKE H R
  • MECHANIC
  • 3,094 POSTS
The car has done it since you bought it maybe there is something changed that you don't know. What about the chip? Could the chip had been changed before you bought the car? I had noticed Summit racing had something to change the timing from one timing to another depending on what timing is for best performance.
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Sunday, June 14th, 2009 AT 7:55 AM
Tiny
FIXALLMAN_77808
  • MEMBER
  • 9 POSTS
Thanks again for this info. I will check for a chip or tampering with the computer in my next tuning session. However in my first quote I stated an issue about the timing backing out at higher rpms. I have and 88 5.0 engine in my garage that I had in a Grand Marquie that did not back the timing out. It would stay at top advance after 2000 rpm thru redline. Also this engine is a multi port FI, where the 86 in the stang is a TBI. I thank you again for this info and will continue to work on this.
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Sunday, June 14th, 2009 AT 12:23 PM
Tiny
MIKE H R
  • MECHANIC
  • 3,094 POSTS
Something we have not talked about is the timing timing chain belt wonder if it would make that much of a diference? Or the timing tensioner. If the tensioner was weak and at higher rpm would let the timing to be off and would cause a timing issue. It's is something to think about. I will bring this topic up to other moderators and see if there is something we could be missing.
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Sunday, June 14th, 2009 AT 4:29 PM
Tiny
FIXALLMAN_77808
  • MEMBER
  • 9 POSTS
To the best of my knowledge, and due to my experience disassembling and reassembling a 1979 302 in a in a ford fairmont, I'm sure that this particular engine design does not have a chain tensioner. The cam gear and crankshaft ger seem to be to close together to need a tensioner. And finally, I've checked the timing and it is stable for an engine with this much milage with only about 2 to 3 degrees of timing fluctuation under no load conditions. I believe this slight fluctuation cannot be resposible for a 20 plus degree retard after 2000 rpm. But i'm still learning.
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Sunday, June 14th, 2009 AT 4:51 PM
Tiny
2CARPRO JACK
  • MECHANIC
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Have you checked fuel pressure with a manual gauge? If the engine is real lean, the computer may be backing down the timing to keep it from pinging.
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Thursday, June 18th, 2009 AT 9:49 AM
Tiny
FIXALLMAN_77808
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No, I have not. That is on my to-do list and I will see if this tells me anything. I think as you do this could be the issues. I'm looking to get a guage soon. Budget is what it is. What should I see in pressure? Any idea?
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Friday, June 19th, 2009 AT 10:57 PM
Tiny
2CARPRO JACK
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Looks like 13-16 psi with a volume output of 1 pint in 30 seconds while cranking the engine
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Saturday, June 20th, 2009 AT 8:08 AM
Tiny
FIXALLMAN_77808
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  • 9 POSTS
Is this on the TBI system, or a carb. This engine is currently set up with the TBI.
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Sunday, June 21st, 2009 AT 1:18 AM
Tiny
2CARPRO JACK
  • MECHANIC
  • 11,533 POSTS
Thats what Mitchell calls for with TBI, they are low pressure compared to the new stuff
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Sunday, June 21st, 2009 AT 9:41 AM
Tiny
FIXALLMAN_77808
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  • 9 POSTS
Good info to know. Thank You.
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Tuesday, June 23rd, 2009 AT 7:55 PM

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