Strange Missfire/adjustable With Timing

izodhalo

New Member
Oct 30, 2013
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Ok, I have posted before about a miss/hesitation in my almost bone stock 90 LX 5.0 5spd. I have tried a few things and I still have a quite a few more things to try/test but I wanted to tell a little bit more to see if anyone has had the same problem and could direct me on something else to test.

The problem: The car has a miss or hesitation under load. It seems to run ok at idle but it doesn't always seem to be smooth, like a very very light miss occasionally. Timing seems to affect the miss while driving but does nothing for idle. The car was set at about 16 degrees initial (93 octane)and drives ok under part throttle and cruising, but shows a distinct miss or stumble when you put the gas to the floor. I have since reset the timing to 11-12 degrees and the miss/stumble is much more noticeable. So much that when you put your foot in the gas more than half throttle, but seems like it hits a wall and misses badly.

So far I have checked for vacuum leaks, replaced the fuel filter, cleaned the IAC, and cleaned the 10 pin connectors. None of the listed things helped at all, only adjusting the timing seems to affect the miss. My next steps are to check the fuel pressure, check the TFI, MAF. A visual inspection of the plug wires seem ok, no damage, but I do hate the straight boots and MAC equal length headers the previous owner installed.

Anyone have an experience like this? Any suggestions other than the ones I've listed?
 
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Do the basic diagnostic steps first...

Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on.

Dumping the computer diagnostic codes on 86-95 Mustangs

Revised 26-July-2011. Added need to make sure the clutch is pressed when dumping codes.

Codes may be present even if the check engine light hasn’t come on, so be sure to check for them.

Here's the way to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

Post the codes you get and I will post 86-93 model 5.0 Mustang specific code definitions and fixes. I do not have a complete listing for 94-95 model 5.0 Mustangs at this time.

Be sure to turn off the A/C, and put the transmission in neutral when dumping the codes. On a manual transmission car, be sure to press the clutch to the floor.
Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.

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If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

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The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.

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The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.


WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and driveablity problems

Some codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, and clutch (if present) is pressed to the floor, and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

Your 86-88 5.0 won't have a working Check Engine Light, so you'll need a test light.
See AutoZone Part Number: 25886 , $10
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Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see www.midwayautosupply.com/Equus-Digital-Ford-Code-Reader/dp/B000EW0KHW Equus - Digital Ford Code Reader (3145It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $22-$36.
 
I bought one of the digital code scanners a month ago because that was my first step. I apologize for leaving that out the first time. I have done just the basic code scan and also the cylinder test. Before I did anything to the car, I had a code for EGR but I have since scanned and it has come back clean, after it does it's thing, it always just shows 11. The cylinder test came back fine, with no problems at all. When I get home I will scan for any codes again.
 
Srthis, a member on here, just found that his balancer had spun on its rubber center attachment. His timing was way off due to this even though it looked correct when timing it. Might want to have a look at your balancer and make sure it is in good condition and you are not running too much timing, or not enough. What about plugs, wires, cap, rotor and coil? What is their age and condition?

Joe
 
My mistake on the codes, I was doing the test wrong. It came back with these numbers:
KOEO-11-10-11
KOER-8-94-44-94-44

Everything else seems in good condition, the plugs, wires, cap and rotor look good. I don't know the age of any of it but it appears the coil is stock. It's strange because the car runs like crap when timed at 12 degrees but slightly better when bumping it up to like 16 or 18. At 12 degrees, it falls on it's face with anymore than 1/4 throttle. Bump the timing up to 18 and it will only stumble at over half throttle.
 
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Ok, after thinking the balancer had spun, I proceeded to verify the timing. The method I chose was to take the passenger side valve cover off, turn the crank bolt clockwise until I first saw the #1 exhaust valve open, then close, then the intake open then close, then marked my position and turned the crank 180 degrees. I then stuck a pencil in the #1 spark plug hole and turned the crank more, then back counter clockwise and a few more tweaks until I could feel (through the pencil) the piston was at the top of it's travel. Only then did I look at the balancer and it was right on 0 degrees. I then took the distributor cap off and the rotor was pointing slightly before #1.
I did notice some vacuum lines off the air bypass valve and air diverter valve for the smog pump tubing. I don't think that could cause this type of problem but I will get some new lines and connect them. Since my only codes were for the air injection system, (94 and 44) I guess my next stop will be the TFI. Anybody have any suggestions based on the info I've given to track down my hesitation/miss problem?
 
Here are pictures of how everything was when I verified TDC.

Based on the pic of my harmonic balancer pointing at 0 and TDC verified, should the rotor be pointing (left) of #1? In the picture, #1 is the closest to the intake or closest to 12 o'clock position. I thought the firing rotation was CCW therefor the #1 would have already fired.

Some more insight would be good. Anyone have any thoughts on this?
 

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