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1994-1995 5.0 Mustang SN95 Tech Forum

5.0L Talk | 5.0L Tech | 94-95 Tech | 1979-1993   1994   1995   Upload Pictures | Timeslips | Power Adders | Mustang Tech 


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Unread 08-14-2011   #1 (permalink)
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Default 1994 Mustang 5.0 Idle? Intake? Fuel Pressure?

Hey guys,

New to the forum! Had to sign up because I just cannot seem to diagnose the issue I'm having with my pony. I am going to be as specific as I can, so that hopefully someone can help me narrow down what's going on.

I bought her back in November 2010 with about 106,000 miles on it. (I have every intention of rebuilding the motor, but for right now she's a daily driver). As of right now the odometer sits at about 120,000, just in case the issue has to do with high mileage.

Anyway, the first issue I ran into (besides body damage, I had a 97 civic ex before lol) was an exhaust leak. Diagnosed, coming from the exhaust manifold (driver's side). A few months later, my car started idling ridiculously high, and every once in a while, I would start it and the idle would fluctuate from about 500 RPM's to 1500. This was a very intermittent issue. So I rolled my sleeves up, replaced the exhaust manifold gasket and bolts and sealed them with some lock tight. Ordered and Intake Air Control module, which fixed the high idle. The 5.0 never purred better. Until a few days later I noticed it that the idle would surge then fall, back and forth, every once in a while though, not all the time. If I try to drive it like this it misfires terribly and has a noticeable loss of power. Then I started noticing why: The fuel pump (normally) whines for about 2 seconds, and then starts perfectly. Now when it fluctuates, the fuel pump doesn't stop whining. And then I noticed it only does this when it's hot outside, or when it's a hot start.

So, I started researching. Talked to a few shops. Replaced the throttle body gasket, cleaned the throttle body, and pretty much cleaned out the whole intake up to the manifold. Had my MAF rewired, and bought a new battery just in case.

Now that I've spent about three hundo, I'm hoping to be making some progress. But she continues to not co-operate. Had another shop tell me he would diagnose for free, tried to pull my codes and couldn't because my cig lighter fuse was fried. He was an idiot. But I looked up the wrong fuse diagram, so we didn't get anywhere there (Figured out why my power seat doesn't work!!). The original shop said something about "relearning my ecu" after I fixed exhaust leak and idle issue, is that the same as just resetting it? Like, pull the neg terminal off the battery for 10 minutes?

So I've narrowed it down to 3 things, I hope. Well two
1. Simple, the fuel pump, just a little more expensive
2. The fuel pump relay, which is housed in the ccrm which is on the radiator core support for this year. It was moved to three different places over a matter of 7(?) years, so it took me a while to locate it. I cant seem to find anywhere though a good diagram of how to check, dismantle, or even locate that specific relay in the ccrm. Is it all one piece?

3. No bueno... my buddy told me the ignition control module was notorious for going bad in these cars. Replaced it today to no prevail.

I really hope someone knows the specific issue and can help out. I know I wrote a lot but I know with issues like this you need to be extremely specific. The only other possibility that has crossed my mind is an electrical problem or a fried computer. But I'm pretty much a beginner. Let me know if you need a list of mods, there's not many.

Thanks guys!!
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Unread 08-14-2011   #2 (permalink)
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Well, you really need to pull the codes. The connector is in the engine bay, passenger side between the firewall and strut tower. You can buy a code reader for under $30 or you can jumper the connection and count flashes.

Save on Equus 3145 at ToolTopia.com

Sorry but I don't have a link for the KOEO jumper procedure.
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Unread 08-14-2011   #3 (permalink)
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Excellent thanks! I'll order it tonight. The only reason I hadn't yet is because I thought they were super expensive. Is there a universal one though or do I have to get Ford specific?
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Unread 08-15-2011   #4 (permalink)
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These are Ford specific for the OBD1 system.
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Unread 08-18-2011   #5 (permalink)
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Got the code reader (actually cheaper on amazon.com!) and just pulled the KOEO codes:
118: Engine coolant temp sensor above max voltage (that's on the top of the coolant reservoir? just replace? Pretty sure thats not the issue)
327: EGR valve position circuit belowmin voltage (makes sense, I dont have an EGR valve.. :/ )
564: electro drive fan circuit fault (when my fuel pump continues to prime, the fan kicks on immediately)

Continuous memory:
124&125:TPS voltage above/below normal, respectively?? (replace?)
157: MAF sensor fault, low voltage (just rewired... replace?)
173: HEGO (HO2S sensor always rich)
177: HEGO (HO2S sensor always rich)

Tried to run KOER wouldn't even pick up the cylinders. The manual said something about the test wouldn't work unless the KOEO sent the pass code, which means no errors (11 or 111)

Thinking the O2 sensors and the tps are the first things I should replace.

Thanks for all your help toyman. This problem has been a huge burden.. I lost a job because my car wouldn't run right, and I've been dumping parts into it for 6 months..

Let me know your recommendations all!!

Thanks Again,
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Unread 08-22-2011   #6 (permalink)
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I have to be honest I'm not very familiar with the electrical/computer system. Do I need to replace one at a time and reset the computer each time? Or should I go ahead and do it all just because of the high mileage?

Thanks guys!
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Unread 08-23-2011   #7 (permalink)
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The ECT sensor is not on the reservoir bottle. It's in the housing above the T-stat where the bypass hoses are. That sensor is #3 in rank. If the voltage is sensed as being high that a cold engine condition and the PCM will be adding extra fuel. Change that one first, erase the codes and check again to see if that eliminated earlier codes.
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