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  #1  
Old 03-07-2016
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Icon5 New to Forum, need EGR help.

I recently bought a 1997 Ranger XLT, 2.3 liter 5-speed. It was cheap and I'm retired, so I have time to work on it. Now, as I'm a Californian, I have to get it smogged.

I'm a fairly competent amateur mechanic, and have a scanner. Here's the deal: The CEL is not illuminated, but my scanner is showing the EGR as non-op. I'm worked on smogger cars for a long time, and I've never seen a bad EGR valve, just ones that needed cleaning or a new vacuum line.

I've located the EGR valve (I think) on the rear driver's side of the engine on the intake manifold, almost against the firewall and inboard of the wiper motor. The line to the valve has vacuum. So, do these trucks (or this engine series) have problems with EGR valves? I can't figure out, if the valve is bad or dirty, why the CEL isn't on.

Thanks for your responses.
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Old 03-08-2016
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Welcome to the forum

CEL should come on when key is turned on, then go off after engine starts, if there are no codes pending.

If CEL isn't coming on with the key then you won't pass smog, and bulb is burned out or CEL has been disabled(bulb removed or taped over).
As far as I know it is against the law to sell a vehicle in most states with disable CEL, although hard to prove who disabled it.


There should be NO vacuum at EGR valve when engine is idling, Exhaust gases are added only when engine is under load, accelerating or going uphill.
The exhaust gases cause air/fuel mix to burn slower, this keeps cylinder temps lower so lower NOx emissions, which tend to spike at higher cylinder temps.
As a side effect it also prevents pinging/knocking on Regular gas when engine is under a load.

To see if EGR valve is opening get a longer vacuum hose and attach it to EGR valve.
Start engine
Suck on the end of the vacuum hose to pull open EGR valve
Engine should start to stumble and may even stall if you hold the EGR valve open long enough.

If this doesn't happen or when you suck on the hose it doesn't hold a vacuum, then EGR valve is bad.

There are 3 parts to EGR system, 4 if you count the computer
EGR Valve
EGR modulator/solenoid
DPFE sensor

You know what the valve does, it opens and closes when vacuum is applied or removed

EGR modulator is a 12volt solenoid controlled by the computer, it has 2 wires and 2 vacuum hoses attached.
Computer will pulse 12volts to solenoid to pull it open and send vacuum to the EGR valve, the speed of the pulses opens it a little or alot, which opens the EGR valve a little or alot.
1 vacuum hose will go to the intake(vacuum source), the other to the EGR valve.
So trace the EGR valves vacuum hose back to the EGR Modulator.

DPFE sensor often fails, it has a wiring connector and 2 hoses, not vacuum hoses but look similar.
One hose will be on or near EGR Valves tube to exhaust manifold
Other hose will be on the exhaust manifold.
DPFE stands for Differential Pressure Feedback
The DPFE sensor tells the computer the pressure difference between the two hoses, when EGR valve is closed pressure would be the same on both hoses.
If EGR valve opens the pressure at the hose closer to the EGR valve will be less than the one on the exhaust manifold, farther away from EGR Valve.

The more the EGR valve opens the bigger the pressure difference, this is how the computer "reads" the amount of exhaust gases it is sending to the intake.

If you have vacuum at the EGR valve while idling, then EGR solenoid is open when it shouldn't be, you can pull it out and test it with 9v battery or car battery, there is no polarity(+/-) it will click open and closed by applying and removing voltage in either direction.

And if you have vacuum at EGR Valve while idling, and idle is smooth then EGR Valve is bad, not opening with vacuum being applied

Last edited by RonD; 03-08-2016 at 11:55 AM.
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Old 03-08-2016
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Icon14

Ron, thanks for your advice. I should have mentioned that the CEL light does work when the ignition is turned on. The CEL light was on when I bought the truck. When I got it home, I looked under the hood and found the PCV valve lying on the valve cover (hose still attached) plugged it back in, put the truck on my scanner, and turned off the light. It remains off, even tho the scanner shows the EGR in-op.

I will follow your advice on locating possible problems and check them out later today. Thanks again for your prompt and informative reply.

Best,

Bob
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Old 03-08-2016
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You're welcome

It is probably an old code in memory then, so problem could have been fixed but previous owner didn't clear the memory.
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Old 03-13-2016
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Update...

(4-day rain delay-it's pouring in California.)

My EGR problem has been solved. My scanner says it works now with the truck thoroughly warmed up. However, on the drive on the freeway, PO171 popped up again.

Watched a Youtube video on this fault and noted the fuel trims, which said my MAF sensor was probably dirty. Given the maintenance level of this truck, wouldn't surprise me.

So, I pulled the MAF sensor from the intake tube and squirted it down good with CRC sensor cleaner. It was definitely in need of a cleaning. Assembled everything back up after checked vacuum hoses and that problem seemed to be solved, but a few miles later it popped up again, although my fuel trims are both just +/- 3 or less.

Today's plans are to replace the fuel filter and air cleaner element (air cleaner is filthy) and see if that helps. Certainly needs to be done anyway.

One thought: Truck was running with no muffler or tail pipe, just a 2 foot long section of pipe out of the converter. I installed the new muffler and tail pipe yesterday. Hmmm? Could that cause a lean condition? Thinking maybe some back pressure to help heat the converter is necessary.
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Old 03-13-2016
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No on the back pressure, that is a myth from the old days of people putting on oversize header pipes and losing power.
Exhaust manifolds actually create a lower pressure in a specific RPM ranger, this creates more available power in that range because exhaust is being pulled out so piston doesn't have to push it out, leaving more power for the rear wheels.
Only a two-stroke engine needs back pressure.

But yes, if there is an exhaust leak on the passenger side(P0171) before the O2 sensor then that will suck in air(see above low pressure in exhaust manifold), this air is seen by O2 sensor which creates a false lean so computer is adding too much fuel to that bank and will set the 0171 code to let driver know.

Also check Long term fuel trim(LTFT) if you have had the Lean codes the LTFT will be high, that will take a few weeks to come back down once problem for lean code is found and fixed.
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Old 03-13-2016
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At the risk of drowning, I checked fuel pressure at the rail (too wet to get under and change the fuel filter) and my fuel pressure at idle is 30 PSI, which jumps up to about 35 when I blip the throttle and then falls back to 30.

Judging by my previous experience with GM cars (3800 series II in Pontiac Bonnevilles) this seems low. Anybody know the spec? Bet it's the filter if it's low-truck has 215K and judging by the lack of previous maintenance I'll bet it's the original.
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Old 03-13-2016
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That is fine for a 1997 or earlier Ranger, spec is 30-40psi, 35-42psi is factory, but 30-35psi is fine, under 20psi would be a problem

1998 Rangers got Returnless fuel system, 60-70 is spec for '98 and up

Partially clogged Fuel filter probably wouldn't show up on static test, fuel use is minimal so Fuel Pressure regulator is sending most of the fuel back to the tank.

You could try raising RPMs to 2,500 and holding it there, watch if pressure starts to go down a bit.
Problem is that a working fuel pump can maintain more fuel flow than the engine can use, even a V8 at full load.
If filter was partially clogged, so less flow, you would have to pass that flow level to see a drop in pressure, and that is hard to do sitting in a driveway, you really need engine to be under a load to get fuel use high enough.

Sign of clogging fuel filter is limited speed on the highway, or losing power going up a long grade

But for $10-$15 it is better to change a fuel filter every 5 years or so and not worry about it.
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Old 03-16-2016
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The quest for a smog certificate continues...

My scanner showed a completely in-op downstream O2 sensor, so I ordered one (and the front one as well) from Amazon. Came today and popped it in no prob, and now after a freeway drive, it's operating, showing voltage right around .11, which I understand is near optimum.

I ordered the front one as when I graphed it on my scanner, it's operating, bouncing from around .090 up to .800 or so, but it seemed lazy, and I also have an "X" on my IM check mode for 02 sensor HRT, so I guess the heater side is duff. Anyway, it was cheap, and the back one is a Motorcraft part, which leads me to believe it's the one that came with the truck.

I plan to change spark plugs and wires, as I don't know their status or mileage. I was a little weirded out to see this truck has TWO plugs per cylinder? Never seem that before. What am I going to do, some hot lapping at Indy?

Eager to see if the front 02 sensor replacement makes my intermittent code PO171 go away without further running the vacuum lines. That would be nice.
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