I have a 92 4x4 with a 5.0 ltr. It will start and run fine till the high idle shuts down after warm up, it then overfuels causing the motor to idle roughly when in gear(some black smoke out the exhaust). Would appreciate any suggestions where to look into the problem, there are no problem codes when truck is koeo test.

 

Couple of things. There is your IAC valve which controls your idle. It is located on the right side of your throttle openings. Take off this unit and scrub up the inside and clean up the throttle butterflys with cleaner and a toothbrush. Also check for a vacuum leak. Could be a hose or like mine, it was a manifold leak. Good luck...

------------------
1993 F-150 4x4 5.0L EFI 5spd. Silver Shortbed..Kelly Safari AWR tires,K&N Air filter,Cat-Back Exhaust. Soon to get: Improved Ignition

 

How do I check for a manifold leak? I have done everything else you mention.

Guy

[This message has been edited by 92F4x4guy (edited 04-11-2000).]

 

One thing that troubled fuel injected Ford's like ours is sensors that confused the computer and made the engine either run rich or run too lean. One sensor called the coolant Temp sensor regulates the rich/lean. It is located on the intake manifold at the bottom of the distributor or towards the top of the thermostat housing. You would be surprised what this $11 sensor can do to your engine. Mine ran completely different. You can tell it made a difference, because in the winter when the engine is cold, usually when you acclerate a cloud will come out very largely, after replacement mine doesn't make such a big cloud. I am guessing that it improved mileage too.

 

Thanks guys. I'll check the intake for leaks first. I'm sure my hayes shop manual has a procedure to check the coolant temp. sensor. The truck seems to loose some power too after it's warmed up.

 

Several ways, but the quickest would be to spray either some carb cleaner or Wd-40 around the manifold where it bolts together as the truck is running and if your motor idle's up, you've found your leak. Be careful with the sprays too! Dah ..Hope this helps........You might have to get a meter (or have someone check) the resistance and voltage of your sensors. They could be still working but out of the specified range (low or high). It sucks when you don't get any codes to work with, even though the truck runs like crap. Patience? Ha...Good Luck.............Les

[This message has been edited by JOHNNY MC (edited 04-11-2000).]

 

I must be overlooking the obvious. The manifold doesn't leak and the Coolant temp sensor is fine(according to the hayes shop manual). Is there an easy way to check fuel pressure? The Tool costs 40 bucks. what should I look for when I have a gauge hooked up to the fuel rail? (ie: pressure at idle, in gear with throttle applied). Do the '92 5.0 truck engines have a Manifold air temperature sensor?
Thanks

Guy

 

Hey Guy...My Chilton's Manual is not the most reliable in exact numbers, but for what it is worth...93-95 had the air intake temperature sensor and says for a 92, it had a air charge temperature sensor. And according to the manual, once you get your pressure gauge hooked up to the fuel rail, at idle it should read approx. 30 psi, and with normal running conditions, it should be approx. 39-40 psi. I would wait for a more reliable source for the numbers, but that Hays Shop manual you have should have some numbers to compare with my worthless Chiltons Repair...Hope this helps some.

------------------
1993 F-150 4x4 5.0L EFI 5spd. Silver Shortbed..Kelly Safari AWR tires,K&N Air filter,Cat-Back Exhaust. Soon to get: Improved Ignition

 

I believe the sensor your looking for is between the 5th and 6th fuel injecter. It is on the intake manifold and is fairly large.

 

Hey,
I had a similar problem on my 86 302. It started running slightly rich, and eventually got so bad it would foul the plugs within a few minutes. After replacing just about every sensor and even the ECM, I found out that the fuel presure regulator had been leeking fuel directly into the vacuum line that connects to it. I connected my handheld vacuum pump to it and it drew gas right through the diaphram. Just something you may want to check if you haven't already.

Later,
Jon

 

End of story...

I went out and bought a new IAC assy, re-gapped and cleaned the new plugs (were carboned up). The problem is gone. I think the IAC plunger might have been sticking. This must have been causing a rich fueling condition by not supplying enough air during idle! As Good as EEC-IV is, It can set codes that have nothing to do with the real problem. I checked everything from spark plug wires to fuel pressure on this one. Thanks for your replies. I learned alot about FI systems with this problem (spent alot of money too)

Guy

[This message has been edited by 92F4x4guy (edited 04-18-2000).]

 

39-40 psi; Those are good for normal operations, not sure about idle, unless its a mechanical fuel pump..

 

You just replied to a thread that's been dead for 16 years.

 

"Dead" just a matter of interpretation.

My truck is 32 years old, not much information lately for a 1985 Ford 150 w/302 EFI. Loads of information in the old threads.

This guy posted his fix, most just pillage and go away........


1985/86/87 F-150 5.0L MFI/EFI

30 seconds is an interesting time-frame; after cold startup (ECA Open Loop Operation), the first 30 sec you should be pulling 15-20 in of vacuum. Then can spread between 7-20 in. for the next 30 sec to 2 min, if you stay idling or are using the throttle in park.

Inputs to the ECA (Cold Start)
ECT Sensor - Engine Temp reading is about 3.52 vdc when cold.
(Shorted is read as 0v or Warm by the ECA (lean mixture occurs))

Air Temp Sensor (ACT) - interrogates Intake or Manifold Air Temperature. Air Temp reading is about 3.52 vdc when cold. (Shorted is read as 0v or Warm by the ECA (lean mixture occurs)) This gets gummed up like the EGR & Throttle Air Bypass.

MAP - is sending intake vacuum pressure frequency signals. (0 in. Hg = 152 Hz. To 20 in. Hg = 101 Hz.

Coil - is providing RPM results.

TPS - Throttle is closed, so the output should be 1.0 vdc on the TPS sensor.
Injectors - are in Full Rich mode for the first 2 min (30sec + 90sec), unless engine warms up quicker as signaled by the ECT. If warm after the first 30 sec, ECA switches to Closed Loop Operation (then more Sensors are at play). (MFI)

PIP - Generated from the SPOUT in TFI in distributer.

Knock Sensor - (if installed) not activated until temp is 140F. (Retards Timing)

Outputs from ECA (Cold Start)

Spout – Timing signal sent to TFI in distributor
Fuel Pump Relay - Comes on for 1 sec when key is turned on. Once engine starts and runs, the ECA gets a PIP signal from TFI in distributor, if it is within 1sec intervals, ECA continues to apply power to the Fuel Pump Relay. Once the engine stops, Fuel Pump Relay is turned off.

Throttle Air Bypass Valve Solenoid (TABVS) (ISC-BPA)- Is allowing air to bypass the closed throttle butterfly. Full Open after startup (11.5 Vdc). After 30 Sec, ECA uses the Map and RPM signals to determine Valve position.(After Throttle is depressed Bypass Valve closes up some during Acceleration due to Map and RPM input signals) (newer models it’s called IAC)

Inputs to ECA after ECA thinks engine is warm (ECA switches to Closed Loop Operation)

EGR Position Sensor -
PIP -
Knock Sensor -
Throttle Position (TP) Sensor –
Engine Coolant Temperature (ETC) Sensor -
Air Charge Temp (ACT) Sensor -
Manifold Absolute Pressure (MAP) -
Coil -

Outputs from ECA after ECA thinks engine is warm

ERG Solenoid/Emissions Solenoids - circuit is turned off for the first 60 seconds, then allows exhaust flow at higher RPM, but not at idle or WOT (old EGR valves, leak exhaust into the intake at idle)

Emissions Solenoids; TAB / TAD / Purge /

O2 sensor - is ignored for the first 2 min, no signal when cold (giving it time to warm up) Range 0.4 Warm to 0.85vdc Hot.

And;
Injectors -
Spout –
Fuel Pump Relay –
Throttle Air Bypass valve -