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Rought idle, louder, power loss... All one problem?

Hey Guys,

I’ve got a problem which my car which developed yesterday and it seems it is getting progressively worse. My car is a 96 Ford Probe GT with a 5 speed. The car has been well maintained and all maintenance and tune up items have been recently replaced, such as plugs, wires (NGK), fluids, belts, and filters. Aside from a crank shaft position sensor wire shorting out a few months ago (some of you may remember), the car has truly run great. With 140,000 miles on it, the car has been running very reliably and smoothly. I have all the records from when it was new.

YESTERDAY, after about a 20 mile drive on the highway in 88 degree and humid weather, I stopped the car for about 15 minutes. After restarting, driving way, then stopping at a red light, I noticed that the car was not idling as smoothly as normal (at the usual 650 rpm range). I needed to get home, so I went on my way, ignoring the rough idle. About 20 miles later, I was accelerating from a stop next to another vehicle, and I noticed (with my windows down) that my car was making more noise than normal. Sounds like the beginning of an exhaust leak, but for some reason, I don’t think that is what it is - especially considering the other symptoms, which I am assuming are related. There may have been a loss of power through all of this, but that might have been in my head. I may have also smelled some gas/exhaust type fumes.

Anyway, TODAY I start the car to go to work. The idle is rough, but I go on my way (seems to run fine otherwise, I don’t think I am harming the car). After a 10 miles stretch on the highway, I exit, and the idle is worse than before. After accelerating from the first stop, there is a noticeable lack of power. While driving the next mile or so, this loss of power is more pronounced. It is a smooth loss of power, no jerky motions, no violent misfires, just a lack of power and acceleration. At this point, I figure the check engine light should be on. Just then, it starts to blink. I pull into my work parking lot, the car idling poorly, and shut it down.

That is where I am right now. I am at work, my car was running poorly (rough idle, louder engine, exhaust gas/smell), and the check engine light is on. I have no idea if the car will start or get me home today. When I leave, if I leave, I plan on going straight to the auto parts store to get the codes read. Until then, I am looking to attack this problem with some knowledge of the issue and the possibilities. Looks like this could be as simple/cheap as an 02 sensor and as much of a pain as a head gasket. Before I jump into this, I am looking for suggestions.

So… Please help me guys! Any comments, suggestions, or ideas?

Thank you.

First order of business: 1. Open hood. 2. Look carefully at engine. 3. Look particularly at spark plugs and wires. Are they all there? A spark plug may have blown out. A spark plug wire may have disconnected. Etc.

The code is 0300… “Single or mulitple cylinder misfire” or something to that effect.

I just checked all of the wires, everything is tight. All of the plugs are also tight and screwed in properly. All air intake hoses seem intact and all sensors are plugged in.

Any suggestions?

An air leak at the exhaust header will allow the engine to suck fresh air into the cylinder through the exhaust port causing the fuel/air mixture to go so lean that you have a misfire.
When the exhaust valve opens in an engine that has the throttle closed, there is actually a vacuum in the cylinder and exhaust gasses rush into the cylinder at first until the piston rises and pushes them back out again. If there is no exhaust leak, then only old exhaust gasses that have had all the oxygen burned out of them reenter the cylinder resulting in no mixture leaning.

Please don’t put NGK plugs in a Ford. It is not that the NGKs are no good. It is just that the Mo’crafts are fine plugs and are probably a better match for the engine.

I just talked to the Service Manager (an honest guy I know pretty well) and his mechanics can’t figure this thing out. They said the catalytic converter is literally getting red hot. They also said the 02 sensor readings were acting up, but I didn’t completely understand what he was saying. I will talk to the mechanic in an hour or so when I get off work and go to get my keys back. I’ll get as much out of him as possible.

Basically, they have no idea. They cannot fix it and don’t want to mess with it anymore… So they are giving the car back to me.

The plugs may not be NGK plugs, they are whatever the Ford dealer recommended.

I will look into the exhaust header… If that is the problem, how do I trace that down? Sound?

One possibility is a plugged exhaust system. That would manifest itself as a rapid loss of power, poor overall operation, a cherry red cat converter, and screwy O2 sensor readings.

After getting the car back from Goodyear, I took the car to a Midas muffler, as it was the only place open on Saturday. Also, I wanted to have the exhaust catalytic converter looked into, which they eventually did.

A cracked distributor cap was found and replaced, but it did not fix the problem. The catalytic converters were visually checked and found to be ok (not melted, clogged, or broken, the engine has been run without them and the problem still exists - rough idle, lack of power.

They found a weak spark (just by looking at it) getting to the back 3 cylinders AND lower compression in one of these cylinders (75 psi, a front cylinder read 140). All three of the back cylindesr were not checked yet. When a plug wire is unplugged from one of the back three cylinders, there is no change in engine performance. Whether this is due to compression or the weaker spark??? The compression test was not real accurate, in my mind, so, I plan to have them do a thorough compression test tomorrow as the next step (now that they have time to do one). Quite a bit of time was spent troubleshooting, but I am clueless as are they. They don’t want me to start throwing money aimlessly at this car and neither do I, so some advice would be GREATLY appreciated.

Ok, a proper and complete compression test was done. All of the back three cylinders (closest to firewall) were 90 plus or minus 5 PSI (adding some oil gave a very small increase in compression). The front were all near 190 PSI.

I have no clue what to do next, the car is back in my hands.

If the compression is good on the front 3, but bad on the back 3, the problem is almost certainly a blown head gasket. Your options are either replace the head gasket, drop in a used engine or get a new car.

Thank you for the reply.

I know you said “almost certainly”, but how can I be sure?

blocked CAT,do a pressure test on the cat,backpressure test.

thats your problem,then find out what killed it.

not even close to a HEAD gasket,very unlikley

The Catalytic converters were all removed after initial engine testing… The engine ran exactly the same. They were not pressure tested, only checked visually. I think the car running identically with and without them is enough to eliminate them. Am I wrong?

nope your are correct. thats alot of work on a probe.

A V6 engine (make, model, year, engine size unspecified) with the rear three cylinders at 90 psi on the compression check, and VWFUELDOOR says it’s not caused by a leaking head gasket. ANYONE got another idea?

I am not sure exactly what you mean… Are you saying you think it IS a timing belt problem?

Anyway, even though most of this is in the original post, its a Ford Probe GT with a 2.5 Liter V6. There is about 140,000 miles on the engine.

I drove the car home last night (a very short drive) and the whole drive home the check engine light was blinking and of course, all symptoms were still there. I am fairly clueless as to what to do next, but I am going to call a few more mechanics in the area and see who might want to mess with it.

I mean it’s “almost certainly” a head gasket because it could also be a cracked head or if things really aren’t going your way, a cracked block at where the head mounts as opposed to the actual gasket. Either way, the head has to come off.

If it were a timing belt or broken cam, you would have zero compression on those cylinders.

I know my lesabre had the same issue I changed everything mass air flow map sensor plugs wires coil packs upper intake plenum I finally figured out it was my ignition coil igniter or ignition control module igniter I don’t anything about your specific vehicle but look into coil packs and or an ignition control module

Jason, welcome to the forum, but the thread is nine years old. My guess is that the problem has already been solved. :grin: