Veeky Forums I need your help...

Veeky Forums I need your help. I inherited a 1984 Mustang GT with the CFI injection and need to get it running semi reliably. I have heard that this year of the Mustang has a defective wiring harness where the insulation can be crumbly. Other than just a couple forum posts I have not seen any proof of this. I know of most of the issues with this era of mustang including issues with cracked floor pans and weird cfi system. Are there any Anons out there that have worked on these type of early fox bodies or that era Ford 5.0 with CFI and could provide some expertise? I would appreciate it greatly. Sorry if I lack the knowledge of board culture here, I mostly lurk over on /k/ and on occasion /g/.

How dedicated are you to keeping it? Any wires over 30 years old can become crumbly. You're better off with making the engine fuel injected or some other system instead of the early 80's weird half carb thing.

part of it is money, It would be much cheaper for me to keep the car with known problems then invest in a new one with unknown problems, and it was my Grandfathers so it is sentimental to a good degree. I am not completely opposed to just ditching it or mothballing it if I have to though. Another idea I had is to ditch the EFI aspect of it and just go pull a carb and intake off an older ford 302. That would make it easier to some degree,just trying to keep cost down.

tell me how much you know about dragon dildos and where you keep em and I will point you in the right direction

Slap on a new intake and carb homeboy

Just slap a carb on it

Eh. I know enough of them to be dangerous and that's about it. What's your question?

As for the harness insulation what you'll see mostly is that the insulation has pulled back from the end of most connectors a bit and exposed the wire. That leads to corrosion and various problems with low-voltage circuits like the efi system

The CFI is essentially the same system based on the EEC-IV found in 85-ish Crown Victorias and Thunderbirds. It operates much the same as the later multipoint systems. However as far as I know no one offers any sort of tune for the CFI, airflow through the throttle body is terrible, and there's not a lot of extra fuel delivery capacity. Which is not a problem because you can't really move much more air through it anyway.

knowing ford it may even be the same intake, I have not seen any difference between the carbed manifold and the efi manifold. My main concern with that is that it has an AOD rather than the T5 so it may be rough in the winter. There is a substantial drop in temp where I live about 100 average in summer to 30 average in winter degrees freedom of course. I could just adjust the ratio if that is an issue. It also has the TRX tire package so it would be a pain in the ass to get new tires for it so I am just going to slap some 15" aluminum rims I bought off someone for 75$ in good shape so not a problem. I appreciate all the info anons.

mostly am just curious as to if you know of any good resources on it or any quirks of the system, based on what you are saying it would seem that I would need to splice in more wires where the insulation has failed and wire on new pigtails to make the efi system happy. I have not had a good look at the car in a while so I will have to go and assess the situation a bit more and determine if that would be good or if I will try to go to the carb.

About the only quirk is that the cylinder-to-cylinder A/F distribution sucks and starves the front two cylinders. Ford's solution was to issue an updated throttle body gasket that partially obstructs the front of the intake opening in order to create a deeper low-pressure area and cause the a/f mix to "hook" around the gasket and towards the front intake passages.

EGR passages like to develop carbon chunks which then get in the EGR valve and block it open partially causing surging and stalls.

Mechanics seem not to understand how the idle speed system system works. There's a base idle speed setting like a carb and then there's an Idle Load Compensator that's used when starting and when A/C is on. Problem is the ILC is operated by vacuum and it's tied in with a vacuum break for the Fast Idle Speed cam. The diaphragm in the vacuum break goes bad and bleeds off vacuum for the ILC causing it not to work. Mechanics get in there and set the idle with A/C on but the ILC inop due to the vacuum leak so the car ends up with a 1200 rpm free idle.

Slap a carb on it and call it good. How far is your commute?

...

The car has a Cold Fast Idle system that operates much like a choke in that you have to press the accelerator to the floor once in order to set it. It has a choke thermostat on the right side that operates the fast idle cam. First problem with these is the previously mentioned vacuum break which is what allows you to kick it down from Cold Fast Idle (about 2500 rpm) to Cold Intermediate Idle (about 1800). If the break is inop you won't be able to kick it down for some time until the Fast Idle thermostat heats up.

Which leads to the next problem. The Fast Idle Thermostat heater is operated by either the 7 volt Field circuit on the alternator (white w/black stripe) or uses a 12 volt supply via a relay that's activated by the Field circuit on the later models. the Field circuit is used so that the choke heater only gets power when the engine is actually running, not just the ignition being on.

Anyway the heater fails so the Fast Idle never comes off and mechanics don't fix the problem they just crank the thermostat back so the the Fast Idle doesn't work. Or the car goes everywhere with a high idle. Fast Idle not working isn't a problem down south but sub-freezing temps may result in cold stalls if it's not working.

cool, that could be what is causing the surging idle and stalls, my grandfather ordered it new off the lot it was one of the first 84 fox bodies in the bay area back in the day so the old gasket is probably still there. Had a problem with that since it was driven off the lot.

less than 3 miles, it takes me about 7 mins to get there on a bad day with about maybe 300 yards total at driving highway speeds so it would not be a bad commute to work at all. Going to be starting school hopefully soon and that is about 15 mins across town but where I live there is little in the way of traffic so it is about 8-9 miles to get there.

>surging and stalling

Another one they like to do is have the O2 sensor cool off at idle and stop reporting A/F mixture changes. It's a one-wire O2 so it doesn't have an internal heater like modern four-wire O2's do. Anyway the O2 cools off and stops reporting rich mixtures and the EEC interprets this as a lean condition so it adds fuel until the thing is almost flooded out and this causes surging as the EEC also sees the drop in rpm from the too-rich condition that it thinks is lean and tries to correct. They really should have had it open-loop under 1000 rpm or so but that probably wouldn't fly for emissions.

cool thanks for the info user, thanks to all in the thread for some great info.

You asked a detailed car question at the right time when an expert was on. Feel lucky.

yes, pretty damn lucky. Hopefully it will counteract some of the bad luck I have had when messing with that car before.

anyhow thanks a ton Veeky Forums for all the info I will put it to good use!

I don't get the haters.

It looks better than the one before, and definitely more remarkable than the one after it.
Last good Mustang was '69 anyway.