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Old 09-27-2016
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Icon5 Confusing codes, hesitation at steady speed

Hi, I have a 1990 4x2 Ranger compact truck, purchased new 26 years ago. The last few months the check engine light has come on intermittently, and sometimes when driving at highway speeds (~60mph) there will be little hiccups in power intermittently. Almost like a sequence of stutters that last just a fraction of a second each. Hardly ever happens at low throttle, but seems correlated with higher load and speed. It's almost like the kind of interruption that you get from really bad gas, but I've tried gas from a couple different stations lately and it never completely goes away.

I have a code reader, so I did the Key On Engine Off readout. In the first set of codes I got the number 52 repeated twice; then the single beep separator for the stored codes; then codes 34 and 41, repeated twice.

Code 52 supposedly means "Power steering pressure switch open." Problem is, my truck doesn't have power steering!

Code 34 supposedly means "EGR control circuit fault." Could that be an explanation for the hesitation that I'm seeing?

Code 41 supposedly means "HEGO (HO2S) sensor voltage low / system lean." Is that the oxygen sensor? I don't think it's ever been replaced... should I replace it?

I recently had the truck serviced by an independent, non-dealer shop; they replaced the fuel filter and pump assembly under the gas tank (to revive the gas gauge operation), replaced spark plug wires and plugs, cleaned the MAP sensor. However, the truck came out of service more or less the same as it went in, other than the gas gauge works again.

I could bring it in and let them take another crack at it, but I wonder if I should just shotgun replace the oxygen sensor and EGR; what do you think?

Thanks for your advice,

Kurt
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Old 09-27-2016
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Power steering has zilch to do with your hesitation.

EGR stands for exhaust gas recirculation. It recycles some of the exhaust to be burned again. Helps the environment and makes the engine run cooler. Could be part of the problem.

H02S is a heated oxygen sensor. H stands for heated, 02 is oxygen, and S i'm sure stands for sensor.

How many miles do you have on your Ranger?

You can replace it if you want, but at this point I see no reason to recommend you to do so. This code is telling you the sensor is reporting a lean condition. Lean = not enough fuel, rich = too much fuel. You can compare lean to meat you find at the market if it helps you remember.


There's two possible theories I have. One, the sensor is bad and reporting a lean condition, which the ECU tries to account for and correct but can't, thus your hesitation.

Two, the engine isn't getting the proper fuel ratio to begin with, the sensor is being truthful to the ECU, and thus the code is set.

If you want to replace something right off the bat; change the fuel filter. An old and dirty fuel filter can restrict fuel flow, causing lower pressure.

Now it is possible the EGR control circuit fault can add to this problem, but I don't necessarily believe it's the root of your issue.


I would suggest a certain piece of scan software, but yours is a 90, pre obdii thus it won't work for you. Unfortunately, without that data, you've got to be rather familiar with other techniques. I hear a vacuum gauge can tell you a lot about an engine.

One thing you could try right now for $0.00. Start the engine when it's cold, then smell the tail pipe then do it again when it's warm. If option 1 is correct, then in theory the engine is dumping more fuel into the engine, and you should smell a rather gassy exhaust. Of course just because it may not be there doesn't mean that possibility is off the table, but it should help clue you in to the problem. Good luck on your journey.

Also, before replacing any o2 sensors or the like, wait for RonD to chime in. He knows more than I do, and can likely shed some further light onto your issue.
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Old 09-27-2016
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OK, I'll do the cold/hot sniff test. The fuel filter was just changed, so I don't think that is the issue. The truck has about 180k in miles.

I forgot to mention that the gas mileage has dropped off... usually in the summer I can count on 27 to 28 mpg, but all I'm getting these days is 23-24 mpg.

Thanks for your help.
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Old 09-28-2016
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+1 to what Arcticwolf said

But IMO O2 sensor should be replaced at least every 150k miles, so yes replace it, I assume you are over 150k

O2 sensors are similar to batteries in that they use a chemical reaction, for O2 sensors this chemical reaction is used to detect oxygen levels in the exhaust.
The chemical does get used up, when that starts to happen they will show false Lean, so computer will start running engine richer, and MPG will fall off over time, it is a slow process not ON/OFF so hardly noticed except in the wallet, lol.
New O2 will pay for itself in MPG over the next 150k

Ford Code 34 means computer is not seeing correct results from EGR sensor, so doesn't know if EGR valve is opening.
In 1990 the EGR sensor may be ON the EGR valve, you will need to look at it, if there are wires on the EGR valve then there is a sensor in the EGR valve.
The computer uses a Vacuum valve to send engine vacuum to the EGR valve to open it.
Follow the EGR vacuum hose back to that solenoid/valve, then follow the other hose on that solenoid/valve to the intake manifold.
Make sure both hoses are good, no cracks, no leaks.
Make sure the wires connected to the EGR sensor, AND solenoid/valve are in good condition, no corrosion inside connectors.

Use current vacuum hose on EGR valve, and suck on it, it should hold vacuum, if not replace EGR valve, it should come with new sensor.
You may need longer vacuum hose for this, start engine, now suck on EGR vacuum hose again, engine should start to run rough as EGR valve opens, and even stall if opened far enough and long enough.
If there is no change then either EGR valve is bad or EGR tube is clogged.

Hard to test EGR solenoid/valve, with engine idling you can apply 12volt and ground to its two connections, valve should "click" open all the way causing EGR valve to open all the way and engine would start to run rough or stall.
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