Bad miss

tda13

tda13

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Okay. Here are the details.

1997 Mark VIII
183000 miles

The car misses when it warms up... not as bad when it is cold. Here are the parts we have replaced (they needed replaced anyway).

Plugs
Coil packs
Fuel filter
Injectors
IAC
EGR

I have NOT replaced the o2 sensors. I'm sure they need replaced, but I have never know o2 sensors to cause a missfire. Bad mileage maybe, but not a missfire.

Also, I am getting a code for the EGR valve sensor. I have a new one, but still have not figured out how to get the old one off (it is mounted to the back of the driver side head between the head and firewall). I'm not sure that's even the problem as I don't really trust the codes.

I did unhook the vacuum line from the EGR and plugged it and drove the car when it was cold and it seemed to eliminate the problem.... the first time. The second time it ran the same with the miss. I'm starting to think I have a bad spot on a cam or a gremlin.

Any ideas.
 
tda13 said:
Okay. Here are the details.

1997 Mark VIII
183000 miles

The car misses when it warms up... not as bad when it is cold. Here are the parts we have replaced (they needed replaced anyway).

Plugs
Coil packs
Fuel filter
Injectors
IAC
EGR

I have NOT replaced the o2 sensors. I'm sure they need replaced, but I have never know o2 sensors to cause a missfire. Bad mileage maybe, but not a missfire.

Also, I am getting a code for the EGR valve sensor. I have a new one, but still have not figured out how to get the old one off (it is mounted to the back of the driver side head between the head and firewall). I'm not sure that's even the problem as I don't really trust the codes.

I did unhook the vacuum line from the EGR and plugged it and drove the car when it was cold and it seemed to eliminate the problem.... the first time. The second time it ran the same with the miss. I'm starting to think I have a bad spot on a cam or a gremlin.

Any ideas.
Click to expand...

Also might add that I have replaced the MAF and cleaned it and the throttle body... also seamfoamed the car.
 
You replaced the plugs...with which new plugs? Gap?
 
My money is on crank angle sensor. When they start to go bad its when they are hot.
 
Any oil leaking from the valve cover gaskets? Did you change the boots as well?
 
Also, just because the coils are new doesn't mean they are good. Ohm them out and let is know what they come back with. That is, unless the boots are junk.

But if it does it worse when warm, I'm leaning to a bad heat soaked coil.
 
94m5 said:
Also, just because the coils are new doesn't mean they are good. Ohm them out and let is know what they come back with. That is, unless the boots are junk.

But if it does it worse when warm, I'm leaning to a bad heat soaked coil.
Click to expand...

The miss is a random miss and is not specific to one cylinder. Boots are new.
 
holy cow, i didnt think you were a member anymore. Im glad to hear the car is still running, although it seems not that well. sorry i cant help to diagnose the problem. good luck!
 
Wouldn't he need a higher output fuel pump for those
 
No, they are not the lightning injectors.
 
Weird problem.

I would get a fuel pressure gauge with a long hose so I could tuck it up by the wipers and still latch the hood.
Take it for a spin and watch the gauge when it warms up.

Running good cold but a miss warm makes me wonder if its a fuel problem.

You have to start to rule things out.
 
And just cause I am a dick I will also throw this out there.

On the dyno my 98 would get random misfires and random timing changes initiated by the computer. New coils, new pump, new injectors etc etc. Well it finally started making noise and I swapped the motor. Upon inspection I find a broken crank trigger ring and figure that was the issue. After pulling the motor apart it seems the key-way on the crank was broken causing the passenger side cams to move a few degrees randomly.


My point being is it can be ANYTHING causing the problem.

Old fuel pumps lose RPM when they get warm and lose fuel pressure.
Old crank triggers start to stick when warm.
IAC motors get stuck and let in more air then the TPS is telling the computer it should see and you get a miss/lean condition.
TPS can have warn contacts that have bad connections when warm or cold.


There are specific checks to rule out each of those things, is there any mechanic buddies by you that can help you perform these tests? If not then your best bet would be to have the car scanned. On the other hand a scan would run about as much as a new pump, TPS and crank sensor so............
 
Are you getting any codes? When my fuel pump was on it's way out it started with random misfires, then started to run lean.
 
Gurahl said:
Are you getting any codes? When my fuel pump was on it's way out it started with random misfires, then started to run lean.
Click to expand...

Yes. I am getting random missfire code (cant remember the number) and it is telling my problem is the EGR valve sensor or an O2 sensor. I have never known an O2 sensor to cause a missfire.
 
Wasnt the EGR valve sensor.... Didn't really think it was, but since I had one to swap out I figured I would give it a try.
 
Could be getting ready to drop a valve, my 83 had the same symptoms after changing fuel filter, dropped tank and cleaned, spark plugs and wires and so on.
 
Funny, my car just started missing last week when it got cold. Having just had 2 COP's go bad I was pretty confident that it's another COP. That's the first thing I'll check anyway. I'm not getting error codes but I didn't get error codes before when I the 2 bad.

I'll take them out and ohm them out but for me I get a quickly repetitive miss when I hit the gas hard or am putting load on the car when I putting a bit too much gas in 4th gear before the car downshifts. Also it starts to miss when the car gets warmed up. Today is bit warmer than the days in the past week and it didn't miss at all today.

--just following up. Ohm'ed out the coil's. Found 3 bad. Replaced and is running great.
 
Starting to smell gas now with the windows down. It seems worse near the back of the car, but it may be my mind playing tricks on me. Car actually seems to be running rich.
 
Is the CEL on?

Smelling gas could be either bad charcoal cans, or you topped off...these cars don't like to be topped off
 
Sapperfire said:
Is the CEL on?

Smelling gas could be either bad charcoal cans, or you topped off...these cars don't like to be topped off
Click to expand...

Yep - CEL is on. I'm going to pull the codes again today. Last time codes told me bad egr sensor and o2 sensor.

Oddly enough, I checked the carbon filters (relplaced them about a year and a half ago) and one of the hoses was disconnected and the plug was unplugged. That pretty much fixed the gas smell and the car seems to run a bit better now. Still missing, but better.
 
Here are the codes (for what it's worth).

P0171 and p0174 - Bank 1 and bank 2 to lean.
Reason - Replace intake manifold gasket.

Thoughts?
 
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