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A bit of background info. . .

88 mustang lx with speed density. Only mod is CAI. 56k kilometres (believe its a canadian model?). Generally good condition.

Here's what's happening. . . Car will run fine when warmed up but from cold it has a bad misfire. I have reset the comp several times (disconnect battery). After reset the car will run rough for a little while then run well, I assume after it has relearnt settings and such. It will run well from cold the next day, but if started again from cold after that its back to stumbling and misfiring.

I'm relatively new to this but here's my .02 anyway. I have noticed a couple of breaks in the sparkplug wires and know this could cause a problem similar to mine but a computer reset wouldnt cause this to go away and come back again, would it? New wires, cap, rotor and coil have been ordered but seem to be taking forever to get here. Also figured it could be a fuel delivery problem so ordered new injectors and fuel filter. I did notice a couple of days ago that I could have an exhaust leak between head and manifold on cylinder #5. Managed to get round to tightening the bolts yesterday (got around 1 1/4 turn out of both bolts) but same problem persists. Ran well this morning after resetting comp yesterday then tried it after it completely cooled down and still misfires and stumbles under load. Could I still have a leak? I figure thats most likely as the o2 sensor would still be telling the comp the engine is lean and over compensating after reset? Does this sound feasible?

Got check engine code 22 KOEO map sensor out of self test range? Do I need a new sensor? Can it be fixed / cleaned?
KOER - 32 - 33 egr below min voltage, not opening. Probably needs cleaning?
91 o2 lean. Exhaust leak? Or other cause? Spark plugs dont show signs of an actual lean condition. If anything they were a mix of reddy brown, which I'm led to believe is normal, and very slightly black.

anyway, sorry for the long post, thanks if you've had the patience to read it. Any help or advice welcome...
 

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Discussion Starter #3
I will be replacing the o2's along with wires, cap, rotor, plugs (no fouled ones at the mo but figured it was time for new ones) coil pack, fuel filter and injectors. I've heard the EGR can be cleaned?

Ive heard you could rule out the map sensor as the cause of the problem by swapping it with another from almost any ford vehicle. Anyone know if this is true? If so, would the fact that mine is speed density be an issue?
 

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I would pay attention to the MAP sensor it sensitive and controls a lot!!

you can swap it out of course I have read that if you disconnect while running the car should change idle, if it doesn't it is probably no good.

I have speed density as well
 
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Well....I can tell you that I had to replace my MAP (Manifold Absolute Pressure) sensor 3 Times on my Late build '87 GT!!......And when I Traded it in for my '89 LX 5.0 Vert., It was going to need a 4th!!.....I am willing to bet that the MAP sensor is the Main cause of your Problems (With the Wires, Rotor, etc.) being Secondary......It was a well known fact back then, that there was Either a Bad design on the MAP sensors, or that where they were mounted (On the Firewall) was indeed a poor location for the 5.0 Mustangs because of the fact that the Housing itself should have been insulated against the Extreme Heat that occurred under hood of those Fox Bodied Stangs.......I would get a Replacement MAP sensor, (Because even if it was replaced sometime in the early '90's) Chances are its Not working correctly.......I have read where Members have Relocated the MAP to the fender-well for better cooling, and some have even wrapped their Sensor in Heatshield insulating wrap......
As Stated above, you Definately Must change those plug wires, and check for (and fix) all leaks, both Vacuum and Exhaust!.......But I will bet you a Dollar to a Donut, its a Bad MAP sensor:gringreen

Sean.
 

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Discussion Starter #6
Thanks for the advice. I take it there is no fixing or cleaning to be done with the map sensor its a case of it must be replaced. Only thing is its taken me over two months just to get the wires and other parts I mentioned into the country and I still cant get my hands on them, and I think I might go nuts if I have to wait another 3 months to get a map sensor brought in.

so anyway, to check if its the map sensor, just disconnect the electrical connector? Or the vac line?
 
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I really don't think that you will be able to really test the MAP while driving the car, because your Fuel Table Maps will be going bonkers inside that PCM. And you don't want to Put it on to much of a Load if you are running Lean (As even those Stock Forged Pistons can be damaged) Try by disconnecting the electrical sensor, and see what it does at Idle, and in Neutral Give her a bit of throttle and see if you can recreate the problem..... (If you remove the Vac line, it will really run like crap due to the Leak.....Get it when the car is running good, remove the Elec. connection, and see if it sounds the same as when its in trouble .....Jeez, it terrible that you cant get parts into your Country.....Have you tried Looking for a source in the Middle East (As I know there is a Bunch of Stang. Lovers there) or what about South Africa?....As they have Ford Dealers in Johannesburg:gringreen .....

Sean.
 

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Discussion Starter #8
Never thought about trying south africa. Might give it a go. Highly doubt they will be able to deliver though. Worth a try.

might see if I can borrow my step dads sensor out of his explorer and see if that works. Any compatibility probs doing this?
 
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That Im NOT sure of....Don't forget, the Expo (Even the Earliest ones were MAF, right?) and I do realize that even AFTER The Stang. converted to MAF '88 California, and '89 for the rest of the US, that the Mustang Kept the MAP sensor as a redundant system, although Im not sure if they are the same as Pre MAF, as the Newer MAF PCM started using the More powerful "A9 EEC-IV" not the earlier "EEC-III PCM's ......But its worth a Try, as you wont damage the MAP from your Dads EXPO because they both run on a 0-5 millivolt electrical signal.....

Sean.
 

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Ok. Started the car this morning, idled a little low at first but then straightened out at around 800 rpm. Maybe the computer still learning the idle after the reset? Idk, but it doesnt usually do this so I thought I'd put it in incase it is relevant.

After the idle even out I unplugged the map sensor and surging ensued. Almost died at one point as well. I take this to mean that the map is functioning correctly, at least at idle? Could it be functional at idle yet not quite fully functional under load?
 

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Discussion Starter #11
Also ive noticed that the fan switches on immediately when you start the car. I thought the car needed to warm up before the fan switched on? Could this mean the car is stuck in closed loop or something like that?
 
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To answer the 1st question....The MAP might be OK at first startup but once it gets Hot it could be malfunctioning........As to whether or Not the Fan should Run upon Startup??....Does your car have a replacement "Electric" Fan?....I ask this, because, On a Stock '79-'95 5.0 Motor, the Stock Setup is a Belt Driven "Clutch" Setup on the Fan......Do you mean that the Fan is Spinning upon Startup?......As this could mean a Bad Fan Clutch......And a True Closed Loop system did Not come into effect until the OBD-II PCM's in 1996 and Later...

Sean.
 

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Discussion Starter #13
The thing is, the car is driving normally after its warmed up? Actually a lot better since I tightened the header bolts and cleaned the plugs. Was still misfiring when cold this morning but didnt seem to last as long (that could be in my head though) . . Also when I started it it had a bit of an idle surge, up and down for about a minute.

and yeah, the fan spins as soon as the engine starts. I take it thats not correct then? Bad fan clutch? Sounds a lot better than stuck in closed loop. Haha. Didnt know there was no true open /closed loop until a specific year. Thought that was standard from SD on through Maf? Sorry to carry on picking your brains but could you explain what you mean by 'no true open closed loop'?
 
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Nah, just check and see (With Engine Off Of Course) if you can Spin tat Fan, by hand, and IF it Spins freely......If you cant Spin it, then you have a Bad Fan Clutch, meaning it is locked and will spin like heck regardless of what the Temp. is........

Sean.
 

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Discussion Starter #16
Hi Sean.

sorry been busy with a recently acquired jeep. Cars will be the death of me. Lol.

anyway, the fan will spin (with engine off, lol.) I wouldnt say freely. I can spin it, let go and it will go on for another few inches. Normal?

Got round to cleaning the plugs again, made a slight difference. Not as much of a misfire when cold but still there. When I cleaned the plugs I noticed a build up of some sort on the plug boots. Pretty much been there since I got the car two years ago so didnt think too much of it. Anyway, I cleaned up the boots (cleaned the all the wires for good measure) and man, what a difference! No misfires from cold anymore! Only problem is its started to do it when warm now. Haha. checked the coolant and it had been getting a little low so topped it up and it took longer for the misfires to start, so I'm going to flush the cooling system today. My question is, do you think that having a misfire for this long could have caused a carbon build up inside the engine? If so, is it possi le to get it out without dismantling the engine?

once again, thanks for helping the noob :)
 
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