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SOHC - 2.3L & 2.5L Lima Engines Discussions and Topics specific to the Lima 4 cylinder engines

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  #1  
Old 05-23-2015
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Chronic Power Loss

My 91 2.3, standard, loses power most times I drive it soon after it warms up. I can't get the RPMs over 2000 and have to pull over. A few minutes later when I start it up it runs okay, but then the problems returns. The computer diagnostic said faulty EGR valve and faulty ECT sensor. I replaced both but problem remains and the codes still come up. No other computer trouble codes come up. This used to happen once a month, but now it's every time. I have put in new plugs, replaced broken timing belt, fuel pump, fuel filter etc. Any theories welcome. Running out of ideas. Thanks. JXM
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Old 05-23-2015
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What were the code numbers?

Faulty ECT sensor could be a wiring problem depending on the code number.
ECT(engine coolant temp) sensor is a TWO wire sensor located on the front drivers side of the engine, below intake manifold, this is only used by the computer.
There is also a ONE wire Sender used only by the dash board gauge.
Did you replace the correct part?

ECT sensor works this way:
Computer sends it 5 volts on 1 wire when key is on
ECT sensor sends back 3 volts on the other wire when it is cold, and this voltage goes down as engine/coolant warms up, when fully warmed up it should be sending back .5volts, under 1 volt.


EGR system has several codes, 31, 32, 33, 34, 35, 84, and 3 main parts.
EGR valve
EGR solenoid
DPFE sensor

Without the exact code number it could be a number of issues.


ECT and EGR are both temp related so it could be either one causing your problem.
EGR system is disabled until engine warms up
ECT tells computer when engine is warmed up

Last edited by RonD; 05-23-2015 at 12:05 PM.
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Old 05-23-2015
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Ron: Thanks for the reply. The codes that came up originally were 33 and 51. To be frank. I didn't pay attention to see if the exact number changed after the repair since the description of the error hadn't. changed.. I replaced the two-wire ECT sensor below the intake manifold. I also replaced the EGR valve itself, not the solenoid. As you suggested earlier, I tested the old one first by sucking on the vacuum line when motor was idling but got no response. Any suggestions welcome. Uncle Buck
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Old 05-23-2015
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code 33 can be ignored because it can come up if computer thinks you are testing the system, and you are not.

Does the new EGR valve cause engine to idle rough when you apply vacuum to it?
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Old 06-01-2015
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re: EGR test

Ron: Sorry it took a while to get back. I put a vacuum on the EGR today and it immediately killed the engine. What does that tell us? I haven't driven the truck in about a week and a half or more, but I assume it will again llose power as soon as it warms up. Thanks. JXM
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Old 06-01-2015
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Ron D: I put a vacuum on the EGR today and it immediately killed the engine which had been idling nicely for 10 minutes. What does that suggest? Thanks. JXM
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Old 06-01-2015
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It means EGR valve is working, and if idle is OK it means EGR valve isn't leaking.

Unhook EGR vacuum line and plug line, go for a drive and see if power is back to normal.
If so then EGR sensor, DPFE, could be giving computer wrong info, check it's two hoses for leaks or water.
EGR sensor tells the computer how far open the EGR valve is, if info is wrong computer could be opening the EGR valve too much, which you see kills the engine at idle and robs it of power at higher RPM.
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Old 06-01-2015
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EGR issue

Thanks, will do. jxm
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Old 06-01-2015
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road test ..

Ron: I plugged the vac line going into the EGR valve and took the the truck for a run. Ran very well for about the first 10 minutes, and then I started getting power loss at about 3,000 rpm which is much higher than before, when I'd lose power at 2,000 and have to pull over. This time it just stumbled a little at 3,000 and I could still drive it almost normally at 40 mph. After a stop at the grocery for a few minutes, I drove home and all seemed fine, again, until I was almost back, and then I had some power loss at 3,000 RPM> So, it's much, much better than before, but still not quite cured. Any advice welcome. JXm
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Old 06-01-2015
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Wondering if your exhaust might be limiting flow, a partial blockage, thinking Cat converter because of the warm up time frame.

My thoughts are that as cat converter heats up it is limiting exhaust flow, when EGR was connected the back pressure in the exhaust system caused more exhaust to flow through the EGR valve than should have, so power loss was felt at lower RPMs.
With EGR not opening you can get more power but still hit a limit because of exhaust back pressure.

You could remove the O2 sensor, giving the exhaust an outlet, and do a test drive, it will be loud, lol, and I guess it needs to warm up to be sure, so watch where that exhaust is going, don't want to melt any wires.

If you can drop the header pipe it might be better.
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Old 06-02-2015
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Ron: I take it that the results so far do not suggest a faulty ERG sensor. Is that correct? I'll do the exhaust test you suggest later this week and see if that helps. Thanks again, JXM
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Old 06-02-2015
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EGR sensor could be bad, but have to find the root problem first, if exhaust system was causing some back pressure that would through off the EGR sensor because pressure differential with EGR valve open wouldn't be as high, so it would set a code.



Exhaust systems, even factory exhaust, are "tuned", usually for mid-RPM range.
Tuned means the diameter of the exhaust port pipe and the diameter of the collector pipe are setup to create a lower pressure at the exhaust valve at a specific RPM.
This is call "scavenging" the exhaust flow.
The port pipe diameter is small enough to create a high velocity flow when exhaust valve opens, when this high velocity pressure wave hits the collector pipes larger diameter, it causes a pressure drop in the other port pipes on that collector, a siphoning or scavenging effect.
This can be a -2psi to -5psi pressure drop at a specific RPM, the diameters and lengths of the exhaust manifold/header pipes and collector is what determines the specific RPM, and those calculations are above my pay grade, lol.

The negative pressure at the exhaust ports means less power is needed to push out exhaust gases from the cylinder, so more power is available for the wheels.
Exhaust manifolds/headers can be tuned for lowest pressure in low-RPM range, mid-RPM range or high-RPM range, most 3rd party headers are tune for low-RPM.
When engine RPMs are near the specific tuned RPM is when you feel/get the extra power.

People who try "free flowing" headers, i.e. just slapping on larger diameter header pipes, will get a reduction in power, "WTF? , this engine must need back pressure", wrong conclusion and where that Myth started, no 4-stroke engine runs better with any back pressure, it kills power real fast.
They eliminated the velocity and negative pressure from the tuned exhaust by using larger pipes, so they lost the power it was creating.
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Old 06-02-2015
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Thanks. I'll remove the O2 sensor this Friday and see what results. JXM
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Old 06-02-2015
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You can also test for exhaust flow issues with a vacuum gauge($25)
In your case you would have to warm up the engine first, so symptom was present, then open and close throttle while engine was running to see how far and fast vacuum dropped and how fast it returned.
I would also hold it at a steady 2,000rpms and see if vacuum held steady or started to slowly drop, meaning exhaust is being held up so engine can't pull in as much air

Good read here on what vacuum gauges can tell you about engine conditions: Technical Articles: Engine testing with a Vacuum Gauge - at Greg's Engine & Machine

Very handy tool to have in the box
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Old 06-02-2015
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Ron: I'm going to buy a vacuum gauge today on the way home from work. Where typically on an engine do you measure the vacuum? Where on a 2.3? Thanks. JXM
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Old 06-02-2015
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Vacuum manifold is the best place, it will have several vacuum hoses attached, and usually an unused port with a cap on it, if all ports have hoses use the EGR solenoid port.

Follow the EGR valve vacuum hose, it goes to the EGR solenoid, which will have another vacuum hose going to the Vacuum manifold.
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