Freshly rebuilt 95 4.0 Running Extremely Rich

[rhekman]

Has anyone had trouble with the Comp Cams 410 cam on the stock EEC-V computers? After a few minutes running my rebuilt motor it's incredibly rich, pouring fuel out the exhaust.

I just reassembled my '95 block with new rings, new rod bearings, new lifters, pushrods, and rockers. Reman heads with stock valves. The rest of the motor is otherwise stock/original except for the upgraded cam with a new timing set.

It first started last night and seemed smooth, but this morning under any load it stumbles and hesitates horribly. I found a fuel leak around one injector, so the upper intake came off and I put on new injector o-rings. Spritzed carb cleaner all around the intake, egr, vacuum lines, throttle body, etc, and found no vacuum leaks. Vacuum gauge reads 18-20 psi at idle.

I took it out on the back roads for a 10 minute test drive, and eventually got a code - "P1131 – Lack Of HO2S Switch – Sensor Indicates Lean". Shortly after I got another code that indicated rich on the other cylinder bank.

I backprobed the MAF sensor and it's returning 1.2 volts at idle, 2.6 volts when I blip the throttle, and seems to scale with throttle input. My scan tool live data reports sane Intake Air and Coolant temps. O2 sensor voltages are .3-.4 volts.

What's weird to me is the live PCM data is indicating a Short Term Fuel Trim of +42% which appears to be extremely high, and corresponds with the rough running and fuel out the exhaust.

Does anyone have any experience with this? Does this sound like bad O2 sensors? or bad MAF?

 

[RonD]

Try the Clear flooded engine test, maybe you have a stuck injector but...............should be getting -43 STFT not +43

+ 43 means computer is opening injectors 43% longer than it calculated to balance O2 sensor on that bank of the engine

O2s only work after engine is warmed up, coolant above 150degF
Before that computer is running fuel trims from memory and O2 data is random

Exhaust manifold leak might cause that, but it would have to be a big leak, creates a False Lean
So any air leak between head and upstream O2 sensor cause False Lean

On my 1994 a shop reversed the plugs on my upstream O2 sensors, so I got rich code on one bank and lean code on the other, lol
On 1995 4.0l O2s passenger side should have a red/white wire, drivers side a yellow/blue




Clear flooded engine
Key on
Press gas pedal down to the floor and hold it down<<<0 RPMs and WOT(wide open throttle) tells computer to turn OFF fuel injectors, to "clear a flooded engine,", spark stays on

Crank engine over
It should not start or even fire, injectors are OFF
If it starts you could have leaking injector or Fuel pump regulator(FPR)

FPR has a vacuum hose attached, if FPR leaks the raw fuel is sucked into the intake via that vacuum hose
But again would expect -43 STFT not +

 

[rhekman]

Try the Clear flooded engine test, maybe you have a stuck injector but...............should be getting -43 STFT not +43

+ 43 means computer is opening injectors 43% longer than it calculated to balance O2 sensor on that bank of the engine

O2s only work after engine is warmed up, coolant above 150degF
Before that computer is running fuel trims from memory and O2 data is random

Exhaust manifold leak might cause that, but it would have to be a big leak, creates a False Lean
So any air leak between head and upstream O2 sensor cause False Lean

On my 1994 a shop reversed the plugs on my upstream O2 sensors, so I got rich code on one bank and lean code on the other, lol
On 1995 4.0l O2s passenger side should have a red/white wire, drivers side a yellow/blue

Thanks, the O2 sensor wiring information is helpful. I've had the sensors off in the past (months before the rebuild) but they might have gotten mixed up. I thought they were fine when I reinstalled them, but the dead cylinders might have masked that issue.

I tried the clear flooded engine procedure, (and TPS value on live data does show 94% at WOT) but the engine fires anyway. I was thinking that was just from extra fuel lingering in the intake from previous starts, and I found it confusing if there was an injector/FPR leak why the computer would be calling for more fuel, not less.

 

[RonD]

Test throttle cable for length
Engine off
Use a stick to push, and hold, gas pedal down to the floor
Then check at engine end to see if throttle is at WOT, try to open throttle more, if it opens more then cable has stretched so you are not getting WOT for the test, so injectors are not turning off
Google: Ford Ranger throttle cable mod

You just need to add some zip ties at the cab end of throttle cable to get WOT back
Then retest

On a fuel injected engine the injectors are shut off by key off, and engine then goes from say 700rpms down to 0 rpms, so there would be NO residual fuel left in the intake of the engine, it would have all be sucked out as rpms dropped down and evaporated by heat of engine and exhaust

Yes, that is what is odd, should have rich(-43) after warm up if it is indeed running rich

And have to mention this for any 3.0l or 4.0l that uses a coil pack
Coil pack spark plug wires should be like this
3 4
2 6
1 5
front

The 5 6 4 side often gets mis-wired, so follow #5 wire around the intake and to the center cylinder spark plug on drivers side
Same for #6 and then #4
Easy to goof up drivers side spark plug wires
This is the firing order for the Ford 3.0l and 4.0l V6 engines

 

[rhekman]

Test throttle cable for length
...
On a fuel injected engine the injectors are shut off by key off, and engine then goes from say 700rpms down to 0 rpms, so there would be NO residual fuel left in the intake of the engine
...
Yes, that is what is odd, should have rich(-43) after warm up if it is indeed running rich

And have to mention this for any 3.0l or 4.0l that uses a coil pack
...

The 5 6 4 side often gets mis-wired, so follow #5 wire around the intake and to the center cylinder spark plug on drivers side

Good Stuff RonD.

TLdr; bad bank 1 O2 sensor.

Oddly enough I modded my throttle cable last winter when the throttle stuck on in a -10F blizzard. During the rebuild I completely disassembled the TB to clean it. I also reset one of the return springs, added lithium grease to the linkage, and ground off the back of the throttle blade screws. Foot to the floor and the throttle blades goes completely flat, even though the TPS only reports 94%; not sure if that's enough for the PCM to register WOT.

I tried the clear flood mode, but got scared when the engine immediately roared to redline. After that, I just unplugged the emergency fuel shut off switch above the passenger kick panel. There was literally so much fuel pooled, the engine started and continued to run for 5 seconds before dying.

Amen about the firing order. On first start last Friday before the rich issue became apparent, I noticed a stumble (not at idle oddly enough) and rechecking found I had the plug wires swapped between cylinders 4 & 5. I had literally checked page 1 of chapter 2C in the Haynes manual only two minutes before and got the order mixed up in my head by the time I got under the hood. Ford really should have put the coil-plug arrangement on a sticker between the spark plug specs & serpentine belt routing.

I stopped at O'Reilly's this morning and picked up a new MAF and upstream O2 sensors. Installed the MAF first since it was cleaner and easier, but rich condition returned after 2 minutes.

I then proceeded to replace both upstream O2 sensors one at a time. Neither were dead according to scan tool live data, but the old bank 1 (right side) sensor was basically stuck at 300 millivolts and never changed. That happens to be the bank containing my formerly cracked cylinder head, which is why I didn't notice the problem before the rebuild.

Early this afternoon I put 30 miles on the truck while returning rental tools to O'Reilly's. The first 1/2 mile looked like I was laying down a smokescreen for the USS Nimitz, there was so much fuel in my exhaust. One or more spark plugs were also probably fouled, judging by the rough cruise characteristics. Slowly but surely over the first 20 minutes the motor ran better and better.

It now starts immediately, idles smooth, accelerates without hesitation, and doesn't stutter during part throttle cruise. I'll be focusing on engine break-in for the next 500 miles or so, varying engine speeds, accelerating & decelerating more on the highway, etc.

Thanks again RonD for the attention.

 

[RonD]

Above 90%(4.5volt) on TPS is WOT
Under 20%(0.69-0.99v) is closed throttle

Its a 5volt scale, so never 0% or 100%
20% is 1volt, so 16-19% is normal
90% is 4.5volt, 94% would be WOT for computer

To check for leaking injector do this test
Disable spark, unplug 4 wire connector on coil pack
Cycle key on and off 3 or 4 times
Then do Clear Flooded Engine test again, it won't start of course, no spark

Now pull out spark plugs and check each ones tip for fuel
All should be dry of course
WET tip means leaking injector
If all tips are WET then there is a computer issue most likely

 

[rhekman]

Yup, TPS range the PCM sees is 18% at closed, 93-94 at WOT.

I should have bench tested the injectors before the motor went back together, but this procedure is helpful.

 

[Angie]

A few years back (10) or so, i built a 410 engine and when it was started and ran for the first couple days I could watch the gas gauge drop. it was a rich running unit. after that it mellowed out and ran smooth. I just chalked it up to the ecm re-learning the new settings. My guess is it should calm down over the next few days.

hope that helps

have you taken it out onto the road and opened it up? freeway speeds were a battle watching the gauge... LOL good luck and i hope it mellows out for you.

 

[RonD]

The +43% is why its running Rich, so leaking injectors probably are not the issue BUT it should also NOT START using clear flooded engine so..................that points to a problem, maybe in the computer

I use clear flooded engine every morning on my high mile 4.0l to pump oil thru the engine before I release gas pedal and let it start

And I can't think of a reason it would go to +43%, a sensor issue or vacuum leak is +20 to +25, lol

 

[Angie]

found my old thread on this topic... cheers

New build burning rich

Hey guys, I finally got around to finishing my 4.0 build up and placing it into the ol'92. Background info: new: all bearings - timing chain - gaskets - all seals - lifters - filters - thermastat - plugs - push rods (5.5" custom) - rings - cam 410 cleaned: injectors - heads P&P - block (A...

www.therangerstation.com

 

[rhekman]

A few years back (10) or so, i built a 410 engine and when it was started and ran for the first couple days I could watch the gas gauge drop. it was a rich running unit. after that it mellowed out and ran smooth. I just chalked it up to the ecm re-learning the new settings. My guess is it should calm down over the next few days.

hope that helps

have you taken it out onto the road and opened it up? freeway speeds were a battle watching the gauge... LOL good luck and i hope it mellows out for you.

Yes I've taken it out and opened 'er up. I put 160 miles on this morning, mix of back roads and freeway 70+mph. Replacement O2 sensors have fixed the dead rich condition. Now, the fuel trim on the scanner fluctuates between +10/-10 depending on conditions as expected. Gas mileage is also back to "normal" where those 160 miles used less than half a tank. I haven't refilled yet, but I'd guess around 18mpg, and that's with me laying into it a little and downshifting to 4th every few miles to vary the RPM during break-in.

I think there's still a little stumble during part throttle cruise, and I think it's worse when the engine is cold (running open loop). I haven't had a chance yet, but I'll be checking for leaky injectors and fuel pressure regulator later this week.

 

[RonD]

Check or replace ECT sensor, computer bases Choke settings on coolant temp so it needs to be accurate during warm up
Too little or too much "choke" will cause running issues

 

[Angie]

don't worry about it much over the next while, call it a break in period. run it for a few 100 miles and i bet it will settle down and be a good unit

i was worried about mine also, then it seemed to take care of itself

 

[Angie]

Any update on this? how is it running now?

 

[rhekman]

Any update on this? how is it running now?

It is running better. I unexpectedly had to go dog/house sit for my sister this weekend, so I haven't had a chance to test for injector leaks. However the flood mode start procedure doesn't actually fire the engine now, so at least it appears the regulator or injectors are not leaking bad enough to flood the intake. I'm still suspicious of a worn or sticky injector(s) because occasionally during highway cruise it responds less smoothly than I'd like during changes like passing or hills.

Cold start/running seems fine now. The IAT and ECT values on the computer match at key-on when stone cold. Once warmed up, the IAT matches ambient air temps plus a few degrees, and ECT hovers around 195*. I do have a small exhaust leak I can only hear under hard acceleration. It doesn't "tick" so much as "woosh", so I suspect the header pipe/manifold ball flange. I'll be sure to troubleshoot that so I'm not messing with O2 sensor function.

First tank of gas netted 17.9 mpg with mostly a mix of 50, 60, and 70mph highway driving. That's only 1 mpg shy of what I was getting last summer before the head started cracking.

Overall break-in seems to be going well. I few little niggles to take care of with the motor, which I'll report back once I figure out. Next on the list are replacement front levelling coils, radius arm upgrades, and new front tires to replace the badly cupped pair I've been dealing with.