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Item Posts    Sort Order

rough idle

 
fatboy891
New User
Posts: 7
Joined: 03/12
Posted: 12/10/12 03:29 PM

I have an 89 gt convertible. I bought it a few years ago after the previous owner rebuilt the motor.It has stock fuel system, msd distributor and stock coil.Had a/c removed,cats removed,all emissions removed including charcoal canister and all vacuum hoses,but still has O2 sensors. Has a  pretty aggressive cam(don't know specs or type),equal length headers,offroad x pipe,mufflers,CAI,cobra intake and spacer. This car has good power and runs and idles well once warmed up. Wondering why cold idle is so rough? Just trying to smooth out idle. Don't know if its running rich or lean(plugs are ash gray-lean?) Can i play with timing or update fuel system(pump and injectors).If replacing fuel system how big do you go?I'm a body guy any  help is appreciated Thanks  

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waynep71222
User
Posts: 96
Joined: 04/12
Posted: 12/10/12 09:01 PM

you will need to know what the system is doing..   since its missing many of the sensors..  

with that many changes.. its probably got a specially programmed computer..

there is a book you will probably want to read on the EECIV system...

51Z45DNT0JL

Ford Fuel Injection & Electronic Engine Control: How to Understand, Service, and Modify : All EEC-IV Systems on Ford, Lincoln, Mercury Cars and Light Trucks 1988-1993 [Paperback]  Charles O Probst

there is a great tool for seeing what the system is doing.. but its like 500 bucks.. more than anything else i have ever seen for an eeciv

Screenshot

there is more.. the book is not that much money and it will explain how the system works... so you can understand whats going on..  

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pepsi1
New User
Posts: 39
Joined: 01/12
Posted: 12/24/12 09:57 PM

Was it running okay until then? Or did it have a slight problem you lived with.

I wouldn't just start changing parts thats gets expensive really quick. I would start with the basics.

1.Do a cranking compression test.

2.Check the resistence of the spark plug wires, the coil output.

3.Get an idea of what direction to go it. You can have an intake manifold gasket leaking, and small vacuum leak that seals when the engine warms up.

4.I've seen the O'Ring around the injector split and cause that type of problem.

Bob  

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waynep71222
User
Posts: 96
Joined: 04/12
Posted: 12/25/12 06:59 PM

It has stock fuel system, msd distributor and stock coil.
Had a/c removed, cats removed, all emissions removed including charcoal canister and all vacuum hoses, but still has O2 sensors. Has a  pretty aggressive cam(don't know specs or type), equal length headers,offroad x pipe, mufflers, CAI, cobra intake and spacer. This car has good power and runs and idles well once warmed up.
Wondering why cold idle is so rough?


during start up.. the system operates in OPEN LOOP.. where it depends upon preprogrammed injector pulse width... using RPM, TPS, either MAP or MAF along with coolant and air intake temps to calculate the fuel needs..  so it could be rich or lean as so many things could be different than what the computer is programmed for..

once the oxygen sensors come up to temp. and the coolant temp comes up slightly.. the system switches into Closed loop where it calculates fuel injector pulse width off the oxygen sensor signals..

there are a bunch of things that might be done..  verifying that the existing sensors are working and within spec...   TPS... ECT... ACT... MAP or MAF...  and that the idle air control valve is actually moving properly by measuring the voltage while the idle air control valve is hooked up...

since half the injectors are hard to get to...  but the other half are accessible   if you visit a local junk yard.. search through the saabs and the volvos..  look around under the hoods of the late 80s through late 90s models.. some have both sides of the fuel injector connector .. cut out as much of the wires from each half as you can...   use female bullet connectors to join the wires .. this allows you to disconnect one injector..  hook your new extension harness onto the injector and into the injector pigtail .. now you can use  and i hope you have a digital volt meter that reads Ms .. millisecond..  you can then monitor the injector pulse width.. most cars idle at 1.2Ms to 1.4 MS .. warm up is usually 1.8 ms to 2.3Ms pulse width..

since all your additional Emissions equipment was disconnected and removed.. your computer will probably never pass a self diagnostic KOEO or KOER test thats built into the computer..

does your car FAST IDLE when you first start it??? is the idle air control actually hooked up.?? without the idle air control working properly .. there will be TOO MUCH fuel for the amount of air coming into the motor during cold start and warm up...  

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