Running rough and lacking power

Tiny
ALAN54
  • MEMBER
  • 1988 DODGE LANCER
  • 2.5L
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 200,000 MILES
While out on a couple of errands, The car started running rough and lacked any power. On my second stop it was very hard to get it started, had to put my foot on the gas to keep it running. Had the same problem at my next stop, On my way back to the house the car did not have any power and the back hatch area got smoky. At home I found that the carpet that covers the area over the muffler was melted and the bottom of the trunk area was blistering hot. I have not done anything more than look at the muffler or tailpipe, thought I would check here first. Anyone have any idea's?
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Tuesday, September 13th, 2016 AT 4:28 PM

15 Replies

Tiny
CARADIODOC
  • EXPERT
The only way for the exhaust to get that hot is when too much unburned fuel is going into the catalytic converter. The most likely cause is a spark-related misfire that sends unburned gas and oxygen into the exhaust where it burns in the converter and overheats it. By continuing to force the car to go with noticeably-reduced power, the catalytic converter will typically be damaged too. The catalyst overheats and melts, and that blocks exhaust gas flow after that. The symptom after the misfire is fixed is the engine still wont have much power and you will hear a steady hiss from the tail pipe instead of the normal "putt putt".
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Tuesday, September 13th, 2016 AT 10:19 PM
Tiny
ALAN54
  • MEMBER
After the car had cooled down I went out and checked the fluid levels. I found that the coolant level was fine as well as the transmission fluid. When I got to the oil I thought that it looked a little thin. So I smelled it and it smelled like gas. I still have not tried to start it but will as soon as the weather clears a little. Does this information change anything?
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Wednesday, September 14th, 2016 AT 6:19 AM
Tiny
052361
  • MEMBER
After the rain stopped, I started the car. It cranked for about three seconds before starting. Idle was a little rough. Got the put put sound at the tailpipe. What next? I really need my car.
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Wednesday, September 14th, 2016 AT 8:54 AM
Tiny
KEN
  • ADMIN
Hello,

I would remove the spark plugs and do a compression test it sounds like some kind of internal, engine damage could have occurred.

Here is a guide to help you

https://www.2carpros.com/articles/how-to-test-engine-compression

Please let us know what you find so it will help others.

Best, Ken

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Friday, September 16th, 2016 AT 8:37 PM
Tiny
CARADIODOC
  • EXPERT
Yup. The rough running is a concern. That could be caused by excessive fuel flooding one cylinder, and that may clear up quickly as it burns away, or it could be caused by excessive fuel continuing to flow from the injector. My bet is on the second condition because of the previous history of the exhaust system getting hot enough to melt the carpeting.

The injectors have caused very little trouble so I think I'd be looking at some other cause of excessive fuel. The main sensor used for fuel metering calculations is the MAP sensor. It measures intake manifold vacuum very accurately and precisely. There are two things to consider on this car. First, your MAP sensor is not original. It was developed by GM. They had a ton of problems, so they sold them to Chrysler. All of that older design failed a real long time ago, and you have a newer design with a pretty low failure rate. The biggest cause of failure as repeatedly seriously over-filling the gas tank on a hot day, AND immediately driving a very short distance, then allowing the car to sit. Fuel vapors expand and could work their way up to the MAP sensor where it eventually deteriorated the protective jelly in the sensor, then it attacked the circuitry. That was the cause of the failures on the first design. This current design is more likely to cause running problems from too much fuel due to a cracked or leaking vacuum hose. A leak will cause low vacuum which the Engine Computer interprets as high engine load, as in accelerating, and the need for more fuel. Check the vacuum hoses first.

The second problem had to do with these sensors are so sensitive, they could be used to measure engine speed by detecting the very tiny pulses of increased vacuum when a piston draws a gulp of air. They don't actually do that, but there is a diagnostic fault code that can be set related to that sensor being too slow to respond to changes in vacuum. The computer knows the engine is running, and how fast, and it expects to see those tiny signal voltage pulses. The problem was the sensor sits on the right front strut tower and a really long hose connects it to the intake manifold. There's a dip, or low spot in the hose where fuel vapors can condense to a liquid and muffle those little vacuum pulses. The fix for that was to cut the hose near each end, install a pair of vacuum tees, then connect a second hose to run parallel to the original one. The theory, that didn't make sense, was air could circulate through the two hoses and the vapors would be drawn out. Doesn't seem logical, but it worked really well.
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Friday, September 16th, 2016 AT 11:12 PM
Tiny
052361
  • MEMBER
I ran a compression test and the values were from 1-4, 125,130,140,120 at operating temp. The spark plugs were all black and sooty and dry.
I also did a fuel pressure test. With the gauge in line at the throttle body, and the key on I have 34psi. My manual says to remove the vacuum line from the fuel pressure regulatorand start the car. I ccouldn'tfind a line going the FPR. When I started it has squrioted out of the little black piece in the top middle of the FPR. So I turned the engine off and didn't get a running value.
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Saturday, September 17th, 2016 AT 1:44 PM
Tiny
052361
  • MEMBER
The last reply should say that gas squirted out of the little hole in the top center of the FPR.
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Saturday, September 17th, 2016 AT 2:22 PM
Tiny
CARADIODOC
  • EXPERT
I don't check fuel pressure very often so I'm not sure what the specs are for your engine, but from memory, yours is either too high or too low. If you have the more common single injector in the throttle body assembly, those run around 14 psi and have the pressure regulator in there too with no vacuum hose. If you have four injectors, typically used on turbocharged engines, those run near 45 to 50 psi and have the pressure regulator on the passenger side end of the fuel rail. Those do have a vacuum hose but disconnecting it isn't going to change the reading that much. Fuel pressure is lowered when vacuum is real high, as in when coasting from highway speeds.

If you're supposed to have 14 psi and you have over 20 psi, you found the cause of the overheated exhaust system. The mixture will be way too rich.
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Saturday, September 17th, 2016 AT 5:17 PM
Tiny
052361
  • MEMBER
Is fuel suppose to squirt out of the fuel pressure regulator?
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Saturday, September 17th, 2016 AT 5:35 PM
Tiny
052361
  • MEMBER
My manual says that indicates a restricted return line. Could it also indicate a bad fuel pump? Or would a bad FPR cause high pressure also?
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Saturday, September 17th, 2016 AT 6:18 PM
Tiny
CARADIODOC
  • EXPERT
You still didn't say if you have one injector in the throttle body or four in the front of the engine. When you have four, the regulator will open a spring-loaded valve to bleed off excess pressure and the fuel will run back into the tank through the return line. The tension on that spring-loaded valve needs to vary a little. That's where the vacuum hose comes in. Higher vacuum is going to pull fuel from the injector(s) faster. To offset that excessively-rich mixture, the vacuum on the regulator makes the valve open easier, meaning to maintain lower fuel pressure. The net difference between the two forces working on the fuel remains constant. The point is, once the desired pressure is reached, anything higher makes the valve open and the fuel must be able to flow freely, under no restriction, back into the tank. That line can be restricted from being crushed or if it was disconnected and plugged.

The regulator can leak internally, then fuel will leak out the vacuum hose and get sucked into the engine. That has been a big problem with GM trucks. I've never run into that on any other vehicle, but I did read about it happening once here on a Chrysler product.

I worked on so few of your car model that I can't remember if they used a fuel return line, but they almost have to. Regardless, there should never be fuel leaking from anything on the regulator. My suspicion is the return line is blocked or the regulator is stuck causing fuel pressure within it to go too high and it's being forced out through a seam, or seal, or something like that. The throttle body injection system runs at 14 psi. The fuel pump will not cause too much fuel pressure, even if you had the fuel pump for the higher multi-port injection system in the tank. The pump is supposed to be able to build too much pressure. It's the regulator's job to set the pressure in the system. The pump can pump for all it's worth. All the fuel will flow through the regulator and back to the tank except for the very tiny percentage that stays in the fuel rail under pressure until it goes into the engine.

People have been known to cut a return line that is leaking from rust, and they plug it, then observe the engine seems to run fine. That can happen with multi-port injection systems that run near 50 psi. Some of those pumps can only build up to around 55 or 60 pounds, and that little extra goes unnoticed in how the engine performs.
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Sunday, September 18th, 2016 AT 6:53 PM
Tiny
052361
  • MEMBER
I have the single port TBI. The FPR has a very tiny hole in the middle of the top. That is where the gas was squirting out when I started the engine. I noticed today that when I just turn the key on fuel wells up from this hole and spills into the bowl.
I am going to replace the return line and the FPR. And the speed sensor as well. Do yo think I need to replace the pump as well?
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Sunday, September 18th, 2016 AT 7:11 PM
Tiny
CARADIODOC
  • EXPERT
Hold on. The pump is obviously working so don't open another can of worms. The pressure regulator is leaking through the vent hole so change that. In this case I would trust a used one from a salvage yard because they had such a very low failure rate. Yours is only the second failure I have ever read about on a Chrysler product. If fuel pressure is still too high, THEN inspect the return line for damage and replace it if necessary. People accuse us all the time of trying to sell them parts that aren't needed. You're proposing to do the same thing.
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Sunday, September 18th, 2016 AT 7:39 PM
Tiny
052361
  • MEMBER
You are right about that, people do say that. But in this case all the parts are close to 28 years old. The returnline is the last rubber that I haven't replaced. I can't find a FPR anywhere in the city except at salvage, I get a lot of parts there.
I should be able to get this all done by Tuesday. I'll let you know how it works out.
One last thing. Did the compression values look good?
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Sunday, September 18th, 2016 AT 7:55 PM
Tiny
KEN
  • ADMIN
They looked a little weak in a couple cylinders but it should be okay.

Please let us know what you find so it will help others.

Best, Ken
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Monday, September 19th, 2016 AT 9:19 PM

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