Another Tale Of A Rough-running 5.0

fairct

New Member
Aug 5, 2017
2
0
1
Maryville, TN
Hey everyone. Posting here to get some advice about what to do next. Prepare for an enormous wall of text. TL;DR: my mustang hunches above 2k RPM and I'm not sure what to do.

I have an 89 mustang GT. Owned it since 09, not driven it very much at all (~2k since purchased, has ~129k miles), but finally have a garage big enough for it so I'm trying to get it running right.

For the past several years, it's developed a, for lack of better word, miss, while driving. It seems to have gotten worse lately, and I've now pinpointed it to really occur most frequently around 2k RPM and above.

Mods from stock (no, they were already on the car when I bought it):
  • 3.73 rear end
  • Cobra intake (not sure if it's just the upper intake or the whole thing)
  • Stock airbox delete with a cone filter stuck onto the MAF with a radiator clamp (sigh)
What I've done/replaced so far:
  • Fuel filter changed ~1-2 years ago (has maybe 200 miles on it since)
  • Spark plugs replaced around the same time as the fuel filter
  • Rotor and distributor cap this past week
  • Confirmed it was in time (set at 12 degrees without SPOUT) and confirmed it was higher with SPOUT (somewhere above 20, it's difficult to know for sure because of how rusty the harmonic balance wheel is)
  • All of the fuses are good
Tests I've done:
  • KOEO (no codes, but a MAF code was found stored)
  • KOER (no codes, but the first time I ran this it gave a 6 cylinder ID)
  • Cylinder balance test
    • 1st run: Codes 20, 40, 60, 70
    • 2nd run: Code 50
    • 3rd run: Code 50
I checked the number 5 plug and it was pretty dark, and had some residue blown out around the plug. I wiped off the surrounding area and tightened it back down, but still noticed the hesitation/miss.

It's difficult to describe the miss. It's more like it's cutting out. The tach dips down whenever it happens, and it feels very violent. My family has referred to it as "hunching."

Not sure what to do next. Could this be caused by the stubby warm air filter that gets fan wash? The battery positive cable is pretty shot but makes a decent connection. I know it needs to be replaced but I'm trying to prioritize my spending toward making it run right again. I know the fuel gauge doesn't work, nor does the temperature gauge, but I assume they're unrelated. If you've made it this far, congratulations! You've shown a lot of perseverance :)
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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Perseverance or stamina.
That hot air intake is not helping, get a stock air box or intake tube that puts the filter in the inside fender well.
Make sure all your connections are clean and tight, fix the suspect cable. There are four hunderhood ground wires that are extremely inportant to the efi system, battery ground cable to block by the oil sender, one small wire fron negative battery connection to a small screw on the inner fender panel between the battery and the solenoid, there is another small wire from that same screw going down to a cylindrical connection then down into the wiring harness. A wire bolts to the drivers side head in back and connects to the firewall. There is one in the wire injector harness, it comes out of the harness on the passenger side in back below the egr area and bolts to the lower intake.
There is a couple of tech threads that will help too, on the main 5.0 tech page there is 5.0 tech/how to threads, scroll down to troubleshooting, there are instuctions on checking for problems.
Hows that for perseverance, or just being long winded.
 

jrichker

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If the car has set unused for over 90 days, pump or syphon out the old gasoline and put fresh gasoline it the tank. Gasoline has alcohol in it which attracts water and water makes corrosion.

If you have idle or IAC/IAB problems and the engine will not idle on its own without mechanically adjusting the base idle speed above 625-750 RPM, this test will fail with random cylinders pointed out every time it runs. The IAC/IAB must be capable of controlling the engine speed to run in the 1300-1500 RPM range. Playing with the base idle speed by adjusting it upwards will not work, the computer has to be able to control the engine speed using the IAC/IAB.

Do the obvious fix the battery cable and anything else that looks like it needs attention.

Do a full tune up - distributor cap. rotor, spark plug wire, spark plugs, fuel filter. Replace the air filter or service it.

MAF meter on CAI system that needs clocking or protection from engine compartment air turbulence. A cone type filter located inside the engine compartment is almost sure to have surge problems due to the hot, turbulent airflow around it.

Don't do this: it is a big NO NO.





Try cleaning the MAF element & then "clock" the MAF by rotating the entire MAF housing to see if changing its position helps.
 

fairct

New Member
Aug 5, 2017
2
0
1
Maryville, TN
Thanks for the info guys. I wasn't sure if I should use the 'surging idle checklist' since it seems to idle ok, but it stumbles at 2K RPM on up. I'll start checking those things though.

My current idle is around 900 or higher I think. Maybe someone set the idle higher and it's masking a problem I would have seen otherwise...

About the "cold" air intake: any thoughts on where I can pick up the stock air box? I would love to go back to stock but have no idea where to find one. If stockers are difficult to find, is there an aftermarket solution that isn't garbage?
 

jrichker

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Thanks for the info guys. I wasn't sure if I should use the 'surging idle checklist' since it seems to idle ok, but it stumbles at 2K RPM on up. I'll start checking those things though.

My current idle is around 900 or higher I think. Maybe someone set the idle higher and it's masking a problem I would have seen otherwise...

About the "cold" air intake: any thoughts on where I can pick up the stock air box? I would love to go back to stock but have no idea where to find one. If stockers are difficult to find, is there an aftermarket solution that isn't garbage?
How do you spell "J u n k y a r d?

You might try http://www.daves-mustang-parts.com/
or
Mustang Parts Specialties Inc  Statham, GA (770) 867-0863 - I have dealt with them and they deliver what they sell.

since you are in TN, checkout https://www.google.com/search?tbm=lcl&q=used+mustang+parts+Tenn&oq=used+mustang+parts+Tenn&gs_l=psy-ab.3..0i22i30k1.210952.212154.0.212825.4.4.0.0.0.0.213.525.2j1j1.4.0....0...1.1.64.psy-ab..0.4.525...33i22i29i30k1.HnNfavdw7Qg
 

imp

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Jul 13, 2017
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MAF meter on CAI system that needs clocking or protection from engine compartment air turbulence. A cone type filter located inside the engine compartment is almost sure to have surge problems due to the hot, turbulent airflow around it.

Don't do this: it is a big NO NO.





Try cleaning the MAF element & then "clock" the MAF by rotating the entire MAF housing to see if changing its position helps.
@jrichker
I expect you won't agree, but as a quickee, I'd move the MAF sensor to the other end of the shiny pipe. imp
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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Check out lmr (50resto.com) for cai, or shop around for a stock air box and use an k&n panel filter, either one is better than what you have.
Don't forget the discount for stangnet members, there is cj pony parts and american muscle also.
 

jrichker

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@jrichker
I expect you won't agree, but as a quickee, I'd move the MAF sensor to the other end of the shiny pipe. imp
What about the turbulence caused by the 90° bend? Look at the stock system - there is at least 6" before any bend in the pipe.
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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If the maf is placed too close to a bend it changes the airflow, too close to the bend at the tb, like the 90 degree turn in the pic, the airflow will slow down and not give an accurate read.
Place the maf too close after a bend and the turbulence right after the bend can cause erratic readings, sometimes that can be helped by 'clocking' the maf, if you look at a stock maf there is a screen that acts as a 'air straightener',
To get a picture in your head, take a piece of 3 or 4"pvc a foot or so long and use a 90° first then a 45° and then a 45° sweep at the end, I took a siphon gun with about 6psi siphoning from a water can and watched how the mist exited the turn, I noticed the higher the pressure the worse the 90 backed up.
I know, my neighbor thinks I'm strange too.
 
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imp

Mustang Master
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@karthief I gotta admit, you guys are on your toes! I failed to see that elbow in my dark image, but should have realized it was there. OTOH, the MAF could be placed halfway along that long straight-away. In reality, I suspect real laminar flow of air in hardly any of these duct systems is hard to find.

Note the problems started some years ago, getting progressively worse. Hard to blame suddenly appearing turbulence happening, I think. Here's an interesting imponderable. What it had:

blue_m12.jpg


What it has now:
mustan11.jpg


Runs smooth as a baby's ass! Idles perfectly, runs well hot, cold, in-between. Why? I dunno. imp
 

jrichker

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@karthief I gotta admit, you guys are on your toes! I failed to see that elbow in my dark image, but should have realized it was there. OTOH, the MAF could be placed halfway along that long straight-away. In reality, I suspect real laminar flow of air in hardly any of these duct systems is hard to find.

Note the problems started some years ago, getting progressively worse. Hard to blame suddenly appearing turbulence happening, I think. Here's an interesting imponderable. What it had:

blue_m12.jpg


What it has now:
mustan11.jpg


Runs smooth as a baby's ass! Idles perfectly, runs well hot, cold, in-between. Why? I dunno. imp
When you disconnect the IAC does the idle speed decrease? If not, the you have your answer - the computer isn't controlling the idle speed, the screw on the bottom of the throttle body is...
 
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imp

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When you disconnect the IAC does the idle speed decrease? If not, the you have your answer - the computer isn't controlling the idle speed, the screw on the bottom of the throttle body is...
@jrichker
The T.B. is brand-new, off a Ford Motorsports 5.0L HO Mustang engine, sold through SVT in the late '90s. I have the whole new, never used engine sitting in the corner. Danged sure the TB adjustment is as it was from Ford. BTW, I have no problems with this set-up in my '94 GT. imp