Just got a 94. Misfiring issue and too cold outside to look into.

[Stuntman Mike]

Just got a 94. Misfiring issue, currently trying to solve. (Signs pointing to EGR)

I know, first thing is "check the codes!".. but it's been about 20 degrees out and I suspect the previous owner painted over/disconnected the CEL.

So here's the situation. Starts right up fine and runs fine for maybe a minute. Then it misses like a cylinder is completely dead for a minute or two. Then after it runs full power and doesn't miss a beat until shut off again. It more or less had the same pattern when it was 50 degrees out, so I don't think it's related to the outside temp.

Without checking codes (I will eventually when it's warmer, don't yell at me.) can anyone guess what would cause this behavior? I'm leaning towards a sensor issue. Like the computer after warmup sees the readings are fubar and goes back to open loop.

94 2.3 5speed.

 

[RonD]

No, for sure not a sensor.
First, contrary to DIYer beliefs, sensors rarely fail.
For DIYers, 90% of replaced sensors were working fine.
For professional mechanics it's 50% but some bill padding is going on there.

My first guess, and it is a guess, is that you have a failed spark plug and the other one in that cylinder is starting to fail.
Since it starts up fine I would think the exhaust side plugs are working and one is starting to fail.
Only the exhaust side spark plugs work when starting, intake side do start working until engine RPMs are above 400, then they come on line.

Possibility of a failing injector but a longer shot than sensor.
You could try running a can of Seaform in the gas tank and see if things improve, if it's an injector issue.

Pulling out all the spark plugs and looking at the tips will tell you alot about the engine condition.

 

[Stuntman Mike]

I appreciate the help, though I'm in disagreement with where you suggest the problem lies.


Starts up, runs fine for about 1 minute whether I drive it or let it idle.

After that 1 minute, it has:
(if driving) Major bogging for about 1-2 minutes straight. Not a sputter, not a stutter, not a surge. Just runs flat and weak.
(if idling) It tries to die.

After that period of time, it runs 100% fine again until it is shut off and restarted.

--

I drove it 30 miles home and stopped for gas along the way. It did the exact same thing after pulling out of the gas station. Fine, boggy, fine till parked.

It's acting the same under idle or load, and seems to have a very specific time frame which makes me think it's not a component issue.

I bought this truck a couple of days ago. The seller said they bought the truck with a blown engine and replaced it with a different engine. It's possible that he didn't hook up something correctly when he did the job.

 

[RonD]

How do you move from, " Just got a 94. Misfiring issue" and "Then it misses like a cylinder is completely dead" to "Not a sputter, not a stutter. Just runs flat and weak."?

While guessing is easy, after all it is just typing, it is more fun, for me at least, if there is a description of a symptom that remains fairly consistent.

The computer has to run a Choke mode since a physical Choke Plate won't work with fuel injection, cold engine needs extra fuel, high idle and advanced spark timing or it will "bog down"
Choke mode is mainly coolant temp based.
O2 sensors also can't work under 600degF, which is why they are heated and why computer ignores them after startup, so computer is running a pre-set air/fuel mix based on coolant temp for 5 to 8 minutes on cold start, and 2 to 3 minutes on restart.

When you start the engine cold, is the idle above 1,200rpm?
That's the computer going into Choke mode(open loop, cold)

And outside of the bogging for a few minutes, does the idle slowly drop over the next 5 to 8 minutes until temp gauge shows just below 1/2 and warm engine idle is set, about 700-750rpm for 4cyl.
If it does do this then coolant temp sensor is probably OK.

Also if the engine has an EGR valve try unplugging it's vacuum hose and plug hose with a bolt, then drive it and see if it does the same bogging.
Could be a problem with EGR solenoid, EGR valve shouldn't open when engine is cold or right after restart, it would cause what you describe.
EGR system is there to reduce NOx emissions which only happen when cylinder temps get too high, after warm up and when engine is under load.

 

[Stuntman Mike]

How do you move from, " Just got a 94. Misfiring issue" and "Then it misses like a cylinder is completely dead" to "Not a sputter, not a stutter. Just runs flat and weak."?

Sorry if I may not have worded it clearly enough the first time around which is why I went into greater detail on the next post, but I'm still trying to describe the same thing. I said "misses like a cylinder is completely dead for a minute or two" in that when it gets to the running like crap phase, it does it the entire time without variation until it goes to running normal. I've driven 4 cylinder cars running on 3 and it idles and drives the same way, like one isn't firing. Misfire can mean not firing at all, can't it?

Anyway, the truck does not have a tach so I can't tell you for sure how high the idle is at startup. I'm going to install one once it's not so damn cold out.. It sounds pretty normal though, but it may not be hitting fast idle now that I think about it.

Once it starts dying though I have to keep fluttering it to keep it alive. When it's back to running regularly again, after revving it the engine drops to a stable idle at what seems like a normal pace from what I remember.

I'll do some more careful observations tomorrow when I start and let it warm up. As cold as it is outside it takes a good amount of time to even move the temp gauge at all.

Again, thanks for the help and sorry for the initial confusion.

 

[Stuntman Mike]

Broke out the stop watch and timed it.

(from completely cold)

0:00 - 0:30 fast idle
0:30 - 2:30 regular idle
2:30 - 3:30 bad idle
3:30 - 7:30+ running fine

Restart after warm:
0:00 - 0:30 fast idle
0:30 + bad idle

I cut the test short but I'm sure it'll do the same thing after 1 minute of rough running.

 

[RonD]

There are two coolant temp devices on all fuel injected engines.
ECT(engine coolant temp) Sender
ECT Sensor

The Sender will only have 1 wire connected, it is only used by the dash board temp gauge, it uses the engine as the Ground so only needs the 1 wire.

The Sensor will have 2 wires, it is only used by the fuel injection computer, computer sends it 5volts on 1 wire, that voltage passes thru the resistor in the sensor and back to the computer on the other wire.
When cold the resistance in the sensor is weak so computer sees around 3volts coming back, the colder it is the higher the return voltage.
As the sensor is warmed up by the coolant resistance goes up and the return voltage starts to drop, at 180degF sensor's return voltage would be below 1 volt, around .5volts.

Not sure on the '94 2.3l but ECT Sensor should be on the drivers side of the engine, at the front just below intake manifold, you can often see it thru the drivers side wheel well.

When starting the engine the computer always opens the IAC Valve all the way, warm or cold, so fast idle at start up is expected, then computer looks at ECT sensor and sets idle according to coolant temp, i.e. choke mode or no choke mode.
If cold idle should be faster than warm, almost twice as fast usually.

If this is not happening, or not holding high idle when engine is cold, then I would suspect ECT sensor, or its wiring.
Computer puts alot of confidence in the ECT sensor when choosing idle level, spark timing and air/fuel mix.

IAT(intake air temp) sensor plays a smaller roll and would tend to show different symptoms, drop in MPG maybe.

MAF sensor is the Big Kahuna of air/fuel mix sensors, while the MAF sensor can cause the bogging effect for sure, it wouldn't come and go as describe.
Cleaning the MAF sensor should be done every few years or so, just a quick spray with electronic cleaner does it, never use brake cleaner or similar, that will ruin it.
Read here on cleaning MAF: http://www.therangerstation.com/tech_library/CleanMAF.shtml

Dirty or faulty IAC valve would probably show other symptoms.

 

[Stuntman Mike]

Okay. I managed to clean off the paint from the CEL (I was right..) and checked the codes using KOEO method:

116 (O,R) Engine Coolant (ECT) sensor out of range - ECT
335 (O) EGR feedback signal is/was out of range - EVR or PFE
341 (O) Octane jumper installed (information only code to notify you if it is installed)

and the memory codes which I'll clear/deal with after I get the other ones sorted out:
122 (O,M) TP low (possibly grounded or open circuit) - TPS
172 (R,M) Oxygen sensor not switching - system is or was lean - Single, Right or Rear HO2S - Fuel control
173 (R,M) Oxygen sensor not switching - system is or was rich - Single, Right or Rear HO2S - Fuel control
332 (R,M) EGR did not open/respond during test or if memory code, did not open intermittantly - EVR or PFE

So.. prime suspect is ECT maybe? Mine's got the one that's tapped into the coolant line instead of the housing so pretty easy to mess with.

If I can't find my multimeter, would I be able to test it by unplugging the connector and seeing if it starts and runs any different?

 

[RonD]

No, can't test it that way.

Need a volt meter.

Code 116 and 122 could be related, they both share the 5volt power from computer, so both would be effected if there was a problem with that wire/voltage.

TPS(throttle position sensor), code 122, gets 5 volts from computer on one wire, when throttle is closed TPS sends back under 1volt(.69v-.99v is spec) to the computer on other wire, at wide open throttle TPS will send back above 4.5volts.

ECT sensor, code 116, gets 5 volts on one wire(same 5volt wire as TPS), and if engine is cold, say 60degF, it will send computer 3volts on the other wire, when engine is warmed up, about 190degF, computer would see under 1 volt.

So if the 5 volts wasn't 5 volts then both sensors would show codes.
It could be ECT or TPS is shorting and effecting the other sensor, but long shot on that one.

171 and 174 are lean codes, they are not related to above 122 or 116 codes.
Lean code doesn't mean engine is running Lean.
Computer reads the weight of the air coming in from the MAF(mass air flow) sensor data, computer then calculates the amount of fuel to add using the 14.7:1 air:gasoline mix ratio.
It adds that amount of fuel via the fuel injectors, then checks the O2 sensor on each bank to see if Oxygen levels are correct.
If there is too much oxygen in the exhaust then it was a Lean burn, computer adds more fuel to the mix until O2 shows correct oxygen levels for good burn, all this happens in under 1 second.

IF computer has to add too much fuel it will set a Lean code for that 1 bank, and turn on CEL, this is to notify the driver that computer is having to add more fuel than calculated so driver needs to check why.
Engine isn't running Lean, so MPG isn't effected, computer always adds the extra fuel, CEL is so you can check out why.
If you get lean code for both banks that usually means the O2 sensors are working correctly, both failing at the same time would be very very long odds.


To get both codes at the same time means upper intake vacuum leak, or air tube leak between MAF and intake, if ALL the air coming into the engine is not going thru the MAF sensor then computer won't be adding enough fuel, it has to add more fuel to compensate for unreported air, so Lean code set.

Could be dirty MAF sensor as well, MAF sensor uses a heated wire, the more it cools down the more air is reported, if it gets dirty, a coating, it acts like insulation so wire doesn't cool down as much, less air reported than there is and Lean code, both banks.

Could be low fuel pressure, computer expects 30psi of fuel pressure, but has no way to monitor that, if fuel pressure is low15-20psi then less fuel flows in when injectors open, computer see Lean from O2 sensors and has to add more fuel(injectors open longer) so lean code set, both banks.

332 and 341 EGR(exhaust gas recirculation) system issue can cause Lean codes by EGR valve being open when it shouldn't be.

 

[Stuntman Mike]

Found the meter, tested things.

Terminals were pretty gunked. Cleaned em up, ran it, tested codes, and the 116 disappeared.
4.5v on plug. ~55 kOhm @ 50 degrees outside, ~8 kOhm after about 10 minutes parked with engine off from a short drive.


Cleared the codes out and after a 15 minute drive I'm left with:
335
341

172
332

I disconnected and plugged the vacuum line to the EGR, still same symptoms.

Bad/stuck solenoid maybe?

 

[RonD]

341 is just an information code, so ignore it.

With engine idling pull off the EGR Valve's vacuum hose, feel if hose has vacuum, it shouldn't.
If it does then yes, EGR system's vacuum solenoid is leaking, so replace it.

If no vacuum on that hose at idle then follow that hose back to the solenoid where the intake hose(vacuum source) is located, and follow it back to the intake manifold.
Make sure both hoses are "air tight".

If these hoses are OK then you should remove EGR valve and see if it is clogged up.
You can put a vacuum hose on the EGR valve and while engine is idling suck on that hose(apply a vacuum) to see if engine begins to run rough, EGR valve is opening, if open enough it should stall the engine.

 

[Stuntman Mike]

Got out the vacuum gauge/pump and tested the egr.
The vacuum line going to it has a constant but extremely weak pulsing when the engine is running. I've read elsewhere that this is normal.

Applied vacuum to the EGR itself. It holds a vacuum and I can hear a clunk around 5 inHg. This made no difference in idle, so I pulled it up to 15 inHg. Idle still did not change at all.

 

[Stuntman Mike]

Checked the two hoses going to the DPFE, both are flowing exhaust. Now I just have to wait for the temp to go above freezing outside to attempt a removal...

 

[RonD]

Got out the vacuum gauge/pump and tested the egr.
The vacuum line going to it has a constant but extremely weak pulsing when the engine is running. I've read elsewhere that this is normal.

Applied vacuum to the EGR itself. It holds a vacuum and I can hear a clunk around 5 inHg. This made no difference in idle, so I pulled it up to 15 inHg. Idle still did not change at all.

EGR tube or Valve is clogged, or EGR diaphragm is good but not connected to valve so holds vacuum but valve isn't moving.
Engine can not idle with exhaust gases added in even small amounts.

Yes, very slight pulsing vacuum can happen at the EGR valve's hose, and yes that could be considered normal, or within spec

 

[Stuntman Mike]

Pulled the EGR off, as expected, gunk everywhere.

I scraped out the bigger chunks before hitting it with some carb cleaner. The valve actually sealed and opened without leaking... but when I sprayed it in the engine intake side (EGR out) to let it soak, I noticed it running out of the diaphragm vent holes.

Correct me if I'm wrong but I do believe I found the problem.