93 5.0 idle issues, stalling?

surratt · Mar 3, 2015

yeah so i swapped in a 93 5.0 in my 87 bronco 2. Has a c4 transmission. HAvent really dud deep trying to fix it yet but basically I start it up and it idles ok for a little but after a minute of driving or two it will stall at idle or deceleration at times. I can drive it but i have to powerbrake and give it gas. Engine is low mileage and plugs are new.

Pre obd2 stuff is harder for me to diag. Im going to start by smoking it for vacuum leaks. I set the distributer to where i had it before but i dont have a pointer for the crank installed. Need to get that set up and double check the ignition timing. Im using a throttle body/intake off a later year 1998 explorer I believe.

what are some common areas to look at for this idle issue?

RonD · Mar 3, 2015

Well I guess you would start with..........what the heck do you got??? lol

5.0l V8 with a distributor.......what kind of ignition system?
TFI, HEI, points/vacuum advance.

Using an EEC-IV V8 computer I assume since you mentioned not having OBD2
But what year is it.

1998 5.0l intake should still have the injectors for 40psi fuel pressure.
1987 system would have 2 fuel pumps, 7psi pump in the tank, 40psi pump in frame rail under drivers seat.

Computer needs a PIP signal from distributor to time injectors and to even know if engine is running, computer just shuts of injectors if there is no PIP.
PIP signal is the same as the CKP(crank position) sensor signal needed in distributorless engine, i.e. engine will just stall without a steady PIP(RPM) signal to computer.

IAC Valve sets idle, cold idle target is 1,100rpm, warm idle is 650-700rpm
If IAC valve is sticking or losing power then it will close and engine can't idle

RangerSVT · Mar 4, 2015

Since I'm guessing this has happened since install, I gotta ask that all the engine primary sensors have been wired correctly and you are using a matching ecu from the donor year. A 93 5.0 could of had maf or map, which vehicle did the 93 5.0 come from? How is your intake piping run?

Sounds like its running fine in closed loop, but when it goes into open loop, its stalling. I'd check the engine sensors...

SVT

surratt · Mar 4, 2015

Ron its a 5.0 TFI distributor type, eec/IV computer from a 93 i do believe. I eliminated the high pressure pump on the frame and installed a fuel pump for a 98 explorer (high pressure) in the tank. Do not believe the iac is sticking, I cleaned during install and it had this problem with the old IAC. I may buy a new one and start from scratch for shits and giggles though

surratt · Mar 4, 2015

by old IAC i mean the one from my stock 93 intake/throttle body.

surratt · Mar 4, 2015

this is a MAF engine from a 1993 mustang....proper ECU for that model. Wiring is all clean solders. Now when you say how is my intake piping run...I had to close up alot of vaccum outlets on the intake that were not needed. I had no rhyme or reason as to which outlet i used for each vacuum operated item. Smaller one for the fuel regulator, small one for the c4 trans, bigger one for the pcv and a bigger one for the booster. Im assuming it doesnt make a difference how or where you run the vacuum from as long as its getting vacuum?

surratt · Mar 4, 2015

eliminated the EGR with a delete plate by the way

RangerSVT · Mar 4, 2015

What i mean by that is properly spaced maf from tb...

SVT

surratt · Mar 4, 2015

For the intake tube I used the factory setup for a 1998 explorer along with the MAF. So the rubber tube puts the air filter box in the passenger front corner of the engine bay. The MAF is a 6 wire and I just wired the IAT wires from the intake into the MAF

surratt · Mar 4, 2015

Well I spent a few hours messing around today and this is what i knocked off the list
1) confirmed strong spark reaching to all the plugs and the plugs are new and properly gapped

2) fuel pressure at 35 running

3)no leaks at regulator

4)smoked the intake to check for vacuum leaks...system is sealed up tight

5)cleaned the cap and rotor

6)checked base ignition timing and it was close enough around 10 or 11 btdc

7) ive got a fuel injector pulse detector and all the fuel injector seem to be working

8) removed IAC and cleaned it, the valve moves freely but not 100 percent sure it is functional

9) idles around 850 surging and hunting...not sure if its running rough or there is a misfire at idle but it doesnt run smooth. Will not stay running unless i rev it to 1200 or so and will still sputter. It seems to drive fine though with no dead misses

surratt · Mar 4, 2015

im going to get a code checker tommorrow and see if the computer can tell me anything and Ill let you know from there. Im scratching my damn head. Also the oxygen sensors are pretty old......could shitty o2 sensors effect my idle?

RonD · Mar 4, 2015

Surging at idle is either computer "trying" to stablize idle using IAC Valve or IAC Valve isn't responding correctly to computer commands.
IAC Valve uses a Step motor, Stepper, it usually has over 100 unique voltage commands that turn the motor to a specific "step", i.e. motor turns XXX number of degrees in "steps"
So, for example, computer sends IAC Valve "step 20" command, motor turns 15degrees and IAC Valve is open 1/4", "step 40 open 1/2", step 60 3/4", ect.
Computer builds up a memory of what step commands sets what RPM, and it is pretty accurate, if warm engine target idle is 650, computer would be within 10rpms of that.

Warm up engine if possible but you can try this cold.
Have your hand holding throttle open a bit, unplug wires on IAC valve, it should close all the way.
If surging/hunting stops then IAC Valve was causing it, BUT.........it could be because IAC Valve is not holding steady position or computer is telling it to move for another reason.
Next unbolt IAC valve but leave it connected to wiring, turn key on, Valve should open all the way, turn key off and it should close all the way, repeat a few times.

Computer always opens IAC Valve all the way for starting, it then closes it to set idle based on engine temp.

No, O2 sensors are only used after engine is warm and they are not used at idle, computers run rich idles, and they are also not used at WOT(wide open throttle), fuel economy isn't primary concern then, lol.
O2 sensors also only "fine tune" air/fuel mix, MAF sensor is the Primary for 14:1 air:fuel
IAT is also for "fine tuning".
O2 and IAT issues would usually show up as MPG drop(rich) or maybe Pinging/Knocking under load(lean), but engine would run fine otherwise.

surratt · Mar 4, 2015

cool Ill try that check with the IAC and see what happens

RangerSVT · Mar 5, 2015

What Ron said, I also suspect the IAC. Did you install the injectors from the 98 explorer as well as the maf? If you didn't, do it. It will give you slight mpg variances if you didn't...

SVT

surratt · Mar 5, 2015

no i did not swap the injectors...I may purchase a new set soon any way and match them up. ill play around with the IAC and maybe just buy a new one. I can remember if this is the IAC from the old intake set up or the one i got with the new 1998 intake, not sure if they are different. Ill also add that it will die coming to a stop not just at idle, coming to a stop i have to throttle the gas.

93 5.0 idle issues, stalling?

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