Just got my 1988 F-150 back last night. Newly rebuilt 5.0 with basically new everything.
Runs great at highway speeds and but has lousy idle. Idle seems OK when first started but as engine reaches operating temperature, idle stumbles and will eventually cut off unless I nurse the throttle. It has a new IAC and TPS. Vacuum hoses have been checked and appear to be OK.
I picked up the truck about 200 miles away and drove home without any problems until I got off the interstate and came to a stop sign. Looked at everything this morning and noticed the tailgate was getting blackened by the exhaust. Looks very rich and I have to believe this is part of the "idle" issue. I need help.

 

I'm sure you have Error codes! Sounds like it's running in Fail Safe Mode. Run Error code scan.http://www.extreme-check-engine-ligh...%20Decoder.htm or $20./ships next day http://www.handsontools.com/Equus-In...ol_p_5574.html Might check to see if o2 sensor is even connected. Should have been replaced. I wouldn't run an old one on a rebuilt engine personally.

 

Thanks for the information. I will start reading codes tomorrow.
I'm reading the Haynes manual tonight and it says "if the problem is bad enough to cause a non-operational condition, the EEC-IV will switch to another alternate mode, allowing only very limited operation so the vehicle can get to a repair facility. In either case, the fuel injection system will need servicing."
What kind of servicing? Got any idea?

 

Beats me! I'd take that comment w/ a grain of salt. You need the codes. I'm thinking they failed to hook some sensor back up. The Error code scan will tell you alot. Like if the ECU is even communicating. Remember to be at norm. op. temp. when doing the test. I have the Code reader unit I posted the link for. Digital numeric display. $20./ works great & comes w/ a very informative manual. Here's a great Information site on Ford Fuel Injection. A to Z overview!http://fordfuelinjection.com/?p=1 Come back w/ your Code #'s, I'll check back. When you see a # 10 code during the Key On Engine Running (KOER) scan, step on the accelerator once, Turn the wheel 1/4 turn & release. If you miss it, not that big a deal, you'll just get a couple of codes noting the tests weren't preformed. Good luck! Note: After the engine reaches norm.op.temp. is when the ECU enters Closed loop function and attempts fuel trim determined by sensor input.

 

Just finished doing the test. First I did the KOEO and had two stored codes 63 and 33 but it gave me a pass code 11 first. Then I moved on to do the KOER test. My code reader has a cylinder ID code first and read 8. I then did the power steering pressure switch and the brake on/off. The reader then displayed 10 and I did the WOT. The codes that showed up were, 42, 33,73, and 25.
I guess I have to read all the voltages on these circuits to see what's wrong.
Got any shortcuts??

 

The TPS isn't new or not seated correctly or not the right one or not adjusted correctly (there are two types, one is adjustable, one is fixed set. Remove and clean your EGR. Inspect it while off, make sure the diaphragm doesn't leak & it's closing completely, the code suggests it's not closing completely. You need to rev a little higher on the WOT. How old is your o2 sensor? If you don't have a clue, replace it too. At least remove it & douche the crap out of it w/ MAF sensor cleaner or electronic contact cleaner. I'd lean on the guy's that rebuilt it for a little help. I think I would have replaced the EGR if I had the engine rebuilt, even if it didn't seem actually needed, if it was the original.

 

TPS is new but I didn't see the guy use a meter when installing it, so chances are I don't have a good baseline voltage of 1.0V. I'll check that tomorrow along with all the other stuff. O2 sensor is only 2 months old but I'll check the voltage output on that also. EGR valve is cleaned but I will check resistance of EVP sensor to make sure it decreases when diaphram is under vacuum. Last but not least I'll make sure the knock sensor is hooked up and has a 5 V reference signal.
I'll post new readings tomorrow. I think the guy who did the installation would help but he's 200 miles away and I need a reliable truck now.
Thanks for your help and support.

 

Not a great day for me. Started with TPS and found it to be within limits for the voltage and the resistance. Replaced O2 sensor and checked the heater did have battery voltage. Read decreasing resistance with EGR/EVP valve/sensor (with vacuum applied) and found correct voltage on initial read with throttle closed .94V and 4.7 volts with WOT. May be a little off but I think it should work. Did not get any numbers on the KS but I did see that it was hooked up.
Idle fine for approximately 2 minutes then gets ragged and continues to degrade until it shuts off.
The only common denominator I see is the EEC-IV. This is making me crazy.
Help!!

 

Got my sensors and numbers confused. The .94V to 4.7V is for the TPS.

 

Well I have an idle most of the time. Problems found were mostly because before engine was rebuilt, it had started using oil. This showed up indside intake manifold and EGR pipe. Pieces were breaking loose and getting stuck in the EGR valve causing it not to close. What it really needs is to be taken apart and tanked but I have tried cleaning with brushes and throttle body cleaner. I also did the "Sea Foam" treatment and I have to admit, it runs better. Also had a tremendous exhaust leak where installation clown crimped the flange of the right header. Got that fixed.
My next question is, can a FOMOCO part be that much better than an after-market part? I'm speaking of the IAC, I have a new one installed but idle still lopes (but not to the cut-off point).
Any thoughts?

 

When the engine was re-built, did they use the stock camshaft? Speed density is not very forgiving is the EFI camshaft isn't being used.

Another issue could be a faulty fuel pressure regulator. Get a gauge and attach it to the fuel rail. Without the vacuum line disconnected, it should be at 39 psi. If you're seeing more than 40, the regulator needs replacement. Because your issue was sudden and running rich, this is a very likely possibility. The regulator is attached to the fuel rail.

If it is the fuel pressure regulator, change your 02 sensor and change the oil after you've gotten it fixed.

 

Stock camshaft was used albeit a new stock cam. Shouldn't I get a code for the fuel regulator? All I'm getting is a KS, the TPS, O2, and was getting EGR. Engine cranks fine and idles well for about 1 minute (I think this is about how long it takes for the computer to get all initial readings and starts trying to fix itself). Engine seems to run well on the highway.

 

Nope, no codes from the regulator, but will cause the 02 to report it's running too rich. The regulator has no electronics. It's a mechanical device. Only way to tell if its not working is with a fuel pressure gauge. The regulator should also have a vacuum signal which under vacuum should reduce fuel pressure by about 5 psi. Make sure you have a good vacuum signal to the regulator. That might be causing your issues if it only occurs at idle.

 

SUCCESS!!
Thanks Windsor.
I replaced the fuel pressure sensor and idle is great. I have no idea of how many unnecessary tests I ran or how many hours I wasted looking at electrical codes. I guess it's a lesson in basics, all you need is fuel and spark.
If there is a plus side, I do know practically every test code and voltage and resistance reading to be expected from this engine.
Thanks again for the help.

 

Cool deal. If you start hearing a rattling sound in your exhaust, you may have fried the catalytic converter. That happened to me after I had a regulator failure. Too much fuel and the cat sort of self destructs. Maybe you caught it in time. Mine took a while to fail and I replaced it with an aftermarket high flow converter. Waayyyy cheaper than what Ford wants for the stock parts.