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4.0 OHV erratic problems


spittinfire

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I haven't shown my face around here for something like 10 years because I just got burnt out on forums. I've still got the same 1994 Ranger with a 4.0 in it and it now has 403,000 miles and counting. I've got some issues with it that for the life of me I cannot figure out and I'd rather fix this truck then buy a new one. I'll warn you, this is going to get long.

So about a year ago my lower intake gaskets started to leak a little water out the front so I pulled them off and replaced them. Shortly after that I started to get some issues with the idle. It would hang or idle high but fuel mileage never went down and power never changed. I figured I messed a gasket up and had a vacuum leak somewhere. I searched and searched and searched but never found the leak. I eventually just pulled the intake back off, inspected all the gaskets and found no evidence of any leaking and put it back together with new gaskets…same result.

I kept driving it but eventually it started stumbling and power was off. Soon check engine lights followed. I started getting a lean code on bank 2 and the matching O2 sensor wasn’t switching. I replaced the O2s thinking that might be the issue but it changed nothing. Same codes, same issues. I found that if you floored it and held it, eventually it would run correctly after stumbling for a bit and it stay running correctly as long as you were in the throttle hard.

I went rounds and rounds with some different codes but none of them were consistent. I thought I might have a leaking exhaust valve and since I have access to a machine shop I pulled the heads and completely rebuilt them. When I pulled the heads I noticed that bank 2 did in fact look like it had been running lean. After putting them back the same problem showed up.

The O2 sensor isn’t switching because that bank is in fact running lean. This is when I noticed on a data stream while driving that the fuel trim from that bank was about half of the other side. When you stayed in the throttle hard and it started to run correctly then the trim levels nearly matched.

Here is a list of what I have changed or verified against a known good part.

ECM – reman unit – did this after finding some leaking diodes and corrosion on my original ECM
O2 Sensors
TPS
MAF
Coolant Temp Sensor
IAT
Coil Pack
Fuel Pump
Fuel Pressure/Regulator
Fuel Filter
Injectors were cleaned and tested
Cat is not clogged

Keep in mind this is a 94, Federal Emissions truck so it does not have a cam position sensor or and EGR.

I’ve ohmed out injector harness and checked the grounds through the wiring harness going to the ECM and it all checks good. I’ve also verified signals going to and from all the sensors.


That’s a quick recap of what I remember from the past 8 months or so. I don’t work on it regularly as it’s not my daily driver anymore so it’s not as important. Now when I drive it I get no KOER codes but I get 3 KOEO codes and they make no sense to me. 177, 542 and 556

DTC 177
Lack of heated oxygen sensor switches, indicates rich (bank #2)

DTC 542
Fuel pump secondary circuit failure.

DTC 556
Fuel pump relay primary circuit failure.

Keep in mind that this is the first time this thing has ever thrown a rich code during this whole thing. Also, if the fuel pump circuit is failing then why is the pump still working? I took the bed off, cleaned the top of the pump, the terminals and checked voltage going to the pump and found no issue. Driving around with a fuel pressure gauge hooked up I have never once seen low fuel pressure.

Anyone have any idea what might be going on here?
 
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spittinfire

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No one has any ideas? No suggestions?
 

ranger_gord

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Hi Spittinfire,

I have basically the same problem, similar vehicle (1994 XLT 4.0 L 4X4 M5OD etc). I had two small leaks at the front end of the engine so I had the timing chain water pump etc done. It has not run right since. I have the same codes (177, etc) but mine has both lean and rich conditions and the MIL will come on and go off. I have put in almost the same parts as you.
I saw your post and I thought that someone may have an answer as well. I got 22 mpg prior to the fixed leak and 10 to 14 after and it is still that way. Press it to the floor and it hesitates and carries on then like someone turned an afterburner on as long as you held it to the floor. If you let off it starts to stutter and behaves the same way as before.

I am at the point where I am going to remove the PCM and checking to see if all the capacitors are okay and see if I need to repair it. I replaced the Ignition Control module in the front left rad support area and I at least go it to stop stuttering as much to 3500 rpm.

If something comes up as a solid solution I'll post here.

Good Luck
 

cp2295

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I would say possibly a stretched timing chain but you would think in that scenario it would make both banks run incorrectly..? Worth a shot. Have you check the cam and made sure a lobe is not wore flat, lifters are working etc etc. also I assume you have already run an engine compression test? Always good to check the basics like this to verify although they don’t sound like they’d fix the issue, you never know.

Also new also means never ever worked so it may be time to double check all sensors ohms and make sure they are in spec. Just because they are giving a reading doesn’t mean it’s right as you know.

As far as the o2 sensors, have you made sure that the heated part of the o2 is working properly? There should be a 12v supply via a 15a fuse in the power distribution block. And also a corresponding ground for the heater element itself. Also, If you can get your hands on a known good ecm just to use as a tester I’d try that.

Harmonic balancer appears to be in good shape and not wobbling either? Ckp readings could potentially be incorrect if it’s wobbling, still unlikely imo.

The fuel pump relay deal is kind of an odd one, as far as I know all the ecu does is activate the ground on the relay when the engine is running (and also for a few seconds in koeo). Either way I dont see how that would affect engine running considering you have good fuel pressure and voltage back there

Just trying to come up with some solutions but this is a difficult problem. Good luck keep us informed. Glad to see that 4.0 still ticking after 400k!


Sent from my iPhone using Tapatalk
 
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cp2295

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Another thing I forgot to add, I had my 86 bronco 2 2.9 run horrendous at times and fine others. There ended up being a hole in the hose that attaches the fuel pump to the fuel line. Far fetched but maybe worth a shot.


Sent from my iPhone using Tapatalk
 

RonD

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I also have a 1994 and had a shop REVERSE O2 sensor wires when doing the clutch
Ran OK cold but as soon as Closed Loop started it ran poorly EXCEPT at WOT(wide open throttle).
Open Loop, cold engine, and WOT cause computer to ignore O2 sensors

Since O2 sensors have universal connectors there is no right or left as far as plugins
Only 1 wire difference in colors as well.
Engine harness connector has this difference:
Red/Black wire is Drivers side O2
Grey/blue is Passenger side O2

Your comment about WOT running better made me think of this
I got Lean AND Rich codes on opposite banks, because of the reversal


After engine is warmed up and idling, unplug the 2 wires on IAC Valve, IAC Valve should close all the way and engine RPMs should drop to 500 or engine may even stall, either is GOOD, no vacuum leaks
If RPMs don't drop then there is a vacuum leak


Computer expects to see 12volts from the coil part of the fuel pump relay when key is on, thats the Primary power, computer then Grounds that wire to activate/close fuel pump relay.
Computer has another wire connected to Inertia Switch wire, it expects to see 12v(system voltage) here after it closes fuel pump relay, this is the secondary power going to the fuel pump, which turns on the pump.

I would pull out Fuel Pump Relay and check its contacts, they can get corroded.

Inertia switch in cab, passenger footwell or kick panel, should show 5-8v key on, that is the computers monitor voltage, no amps just volts, so fuel pump is off.
It will read Battery voltage(12v) for 2 seconds just after key is turned on, thats the computer Priming the fuel system, it does this EACH TIME the key is turned off and on, so you can test for that, thats the fuel pump relay closing and then opening
When engine is started, it will read 13.5-14.8volts, alternator voltage, if fuel pump relay has closed
 
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telsar

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EGR leaks
vacuum leak
PCV valve
 

spittinfire

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Thanks for the responses guys.

It doesn't have an EGR so I can't check that. I have capped off all the vacuum ports except for the fuel pressure regulator and seen no change, I've also gone over the engine countless times with brake clean and found no leak. PCV is clear. I do not believe this is a mechanical issue but an electronic/sensor issue.

Bank two physically showed signs of running lean when pulled apart which was supported by what the O2 sensors where showing. I believe this to be a fuel delivery issue but I can't understand why it is happening. Bank 2 fuel trip shows roughly 50% of bank one until it "switches" after been held wide open for a period. Once this happens the O2 switches just like it's supposed to.

I'm leaning towards injector pulse being off for some reason or maybe a bad injector. Even though all the injectors ohmed out correctly and sprayed properly when bench tested. The injector harness also tested good. All grounds to the ECM tested good and all the ground in the engine compartment were checked and cleaned.
EEC and Fuel pump relays were replaced and connections were checked.

If I unhook to the AIC it idles at 500 and if it's cold it will almost stall. I've thought about putting a new fuel pump in it but I think it would be pointless. I'm really at a loss here.
 

spittinfire

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So since I last posted I have put a set of reman injectors in it and verified the ignition control module with no change at all. I am running out of ideas and options....
How much does the GEM, if at all, get involved with the ignition system?
 

RonD

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1994 has no Body Computer(GEM), that was first used in 1995 with the newer EEC-V computers
And in 1995 and up GEM only interfaces with Cab(Body) electrics, nothing to do with engine system
 

spittinfire

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1994 has no Body Computer(GEM), that was first used in 1995 with the newer EEC-V computers
And in 1995 and up GEM only interfaces with Cab(Body) electrics, nothing to do with engine system
Thanks for clearing that up. I was getting mixed info in my research on what all it controlled.
 

Bjurovich

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Have you made any progress with this? My 1997 is having an identical issue and I’ve done everything you have to no avail
 

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