Can't figure out Bronco issue

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My 1993 Bronco in my sig is giving me a hard time. It's running noticeably rich, idle surges, and it has a noticeable skip or miss sporadically. I've replaced the MAP sensor, TPS, IAC, fuel pressure regulator, and of course new plugs, wires, dizzy cap and rotor. Issue still remains. I'm wondering if it's a bad injector? Check engine light is on, I bought an obd1 reader, and it would not do an key on engine off test, but it did give me a few codes on the key on engine running test. Main one being thermactor air system malfunction. No vacuum leaks, I had a ford tech check for me. I'm not sure what to try. Any help or advice would be appreciated!
 
First, I know little about Fords, so this is just generic info. The first two things that come to mind are a leaky injector or a bad coolant temp sensor.
 
Unplug the O2 harness and see if it runs normally. The rich surge is a common EEC-IV issue. It can be as simple as a baffed O2 sensor.
 
Originally Posted By: zrxkawboy
First, I know little about Fords, so this is just generic info. The first two things that come to mind are a leaky injector or a bad coolant temp sensor.

I will look into that.
 
Originally Posted By: OVERKILL
Unplug the O2 harness and see if it runs normally. The rich surge is a common EEC-IV issue. It can be as simple as a baffed O2 sensor.

I will try that tomorrow. Glad it only has one to check!

Early EFI Fords are new to me. I grew up with carb'ed SBFs, and Modular Fords that you just plug up to an OBDII reader and find out what's wrong.
 
EEC-IV is something I'm very familiar with due to my past involvement with the 5.0L Mustang scene
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Originally Posted By: OVERKILL
EEC-IV is something I'm very familiar with due to my past involvement with the 5.0L Mustang scene
smile.gif


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Love an old pushrod 5.0. I am going to get one soon, so I better figure this stuff out. I'll try it out tomorrow and let you know if that is the prob.
 
Originally Posted By: Joe_Power
The previous owner wasn't Al Cowlings by chance, was it??

Haha nope!
 
Did you check/adjust the voltage on the TPS to ensure it's under 1v?

Also, what condition are the vacuum hoses in? They become very brittle over time. You might need to replace the vacuum hoses with rubber hoses.
 
Also, check your EGR valve position sensor and the EGR DPFE.

Regarding the EGR valve position sensor, if your EGR valve is an OEM unit, the Motorcraft EGR valve is the only one that will work.

If your EGR valve is an aftermarket unit, the OEM or any aftermarket EGR position sensor will work.
 
Originally Posted By: OVERKILL
Unplug the O2 harness and see if it runs normally. The rich surge is a common EEC-IV issue. It can be as simple as a baffed O2 sensor.


O2 sensor likely lazy. If you can connect a fuel pressure gauge, you can check pressure and for a leaky injector or regulator issue. The pressure should hold for some time after shutting down the engine.
 
Sadly, not really enough info to go on. You have already thrown parts at it, and that makes diagnosis more difficult.

Find someone with an EEC-IV scan tool that can display PIDS. Look at left and right long term trims,compare left and right to determine whether an O2 sensor is bad/slow, or whether a problem is effecting both banks. Look at the IAT data, not an uncommon problem. You are sure idle is rich? Ck your vac line to the MAP. Sometimes an old MAP will leak that gooey sealant into the vac line and cause problems. Sometimes vac lines leak. Agree with the first post in suspecting a MAP sensor/vac problem first.

Oh, if you are getting a thermactor code,ck your diverter/dump valve out . Very possible to have a bad valve/vac solenoid feeding air upstream and throwing your O2s off . Bad injector patterns can cause weird idle problems that dissipate as RPM ramps up. As simple as they seem, this engine combo was not the easiest to diagnose.

EDIT: Unless you are paying good money for a scantool that can do PIDS/data display, this pulls EEC codes to. http://www.thorssell.net/hbook/eectest.html
Ignore the DVOM and use your MIL blinks to see the code.
 
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Originally Posted By: Vikas
Wow, Ford had all that in 1993?


Yes, it took a whole lot of external plumbing to get their old engines to make emissions.
 
No, I meant all the sophisticated electronic sensors and controls and the ability to provide diagnostic details similar to OBD-II.
 
Originally Posted By: Vikas
No, I meant all the sophisticated electronic sensors and controls and the ability to provide diagnostic details similar to OBD-II.


1986 actually. EEC-IV was an incredible system developed by Ford with Bosch and Intel. It evolved to incorporate Mass Airflow a couple years in as well.

It had a number of abilities that generally weren't used on many platforms such as the capability to actuate an electric fan based on a set temperature for example. Devices like the TwEECer could be used to modify things in the ECM and enable those features.

In car applications it featured fully sequential injection (most other systems including Ford's version used on the trucks were batch fire or bank fire) with eight individual injector drivers and complex (for the time) adaptive feedback strategies.
 
Unplugged o2 sensor, idle smoothed out, and the overt fuel smell went away. Still feels like it's skipping at cruising speeds 45mph and up. I should replace it, I suppose?
 
Personal opinion: Hook everything back up, clear codes, warm it up and drive it a few miles then do a KOEO and a KOER to get some reliable codes (hopefully) to help diag the problem.
 
Originally Posted By: austinlunsford
Unplugged o2 sensor, idle smoothed out, and the overt fuel smell went away. Still feels like it's skipping at cruising speeds 45mph and up. I should replace it, I suppose?


When you say "skipping" do you mean like a misfire?

What unplugging the O2 sensor harness does is make it run out of base table and never go into closed loop. The base table values are "correct" for the engine but of course don't account for wear or ambient adaptations, they are basically just (good) guidelines for the ECM that it can improve upon. It then writes its new tables when in closed loop using the feedback mechanisms at its disposal.

When you have something that throws a wrench in the feedback process, you end up with an idle "surge" because the O2 sensor is telling it rich, then LEAN! and then RICH and then LEAN and it's flying back and forth trying to compensate for both of these things, which makes the idle surge up and down.

A misfire can cause the surge because there will be a pocket of "nothing" (or unburned fuel) in the exhaust which, depending on whether it ignites on its way will either trigger a massive rich or massive lean. The other thing is that this all doesn't go out the exhaust, some of the fuel stays in the cylinder and so if the mixture is ignited on the next stroke, that cylinder will be extra rich, further screwing up the feedback loop.

This can also be caused by a bad injector that makes one cylinder rich (or lean).

Also, the ECT (engine coolant temperature) sensor tells the ECM which table to run out of. But usually when this is bad, even in open loop with the O2 harness unplugged it will run poorly.

EEC-IV has the ability to run a cylinder balance test. It shuts off the injector for each cylinder and watches for idle drop based on it. However, since yours is a truck and has the single O2, I believe it is batch fire and won't have that capability
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Which sucks, it is a great diagnostic tool.

What's the background on this problem, did it just start one day? Or has it been just building up and getting worse?
 
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