misfiring troughout RPM range

[cruisintalonawd]

mods are in profile, I have no BLS, I have changed the TPS, coils, CAS, plugs(.028), wires, and power transistor. Car all of a suddenly started doing this while I was boosting down the road.

 

[TwoLiterLaser]

Is there a CEL? What is your fuel pressure? Are all the injectors firing? Start at the basics and work from there.

 

[tjbiker031]

Yeah i would first make sure you have spark on all 4 then you have fuel. You may also be hitting a fuel cut, just something i think about.

 

[djalogik]

Check your spark plugs and wires

 

[twicks69]

*Check the vacuum line that is connected to your adjustable fuel pressure regulator. If it is disconnected, it will cause a lean condition due to the fact that it is no longer a "rising-rate" fpr. Make sure you reinstalled it after all of your replacements. If it is connected, check its base idle fuel pressure to make sure it didn't adjust on its own and lean out on you. If it did, use a second jam-nut to ensure it doesn't adjust on you in the future.

*If this is good, then look at the fuel filter, and your fuel pump wiring. Check fuel pump voltage and current draw to make sure it is within specifications.

*Check your engine grounds.
*Check for boost leaks.
*Reset your ECU and re-tune your vehicle.

 

[TwoLiterLaser]

I have changed the TPS, coils, CAS, plugs(.028), wires, and power transistor.

Woops! Should have read the post in it's entirety! Good job!

EDIT: In reply to the person suggesting he "Check his plugs and wires."

 

[slowstang]

If you changed all those electrical parts with KNOWN good working ones I would check fuel and then the ECU. ECU could be screwing up both fuel and spark. Leaking caps can mess with your fuel.

 

[cruisintalonawd]

No CEL, I am getting spark and fuel to all four, I don't think its fuel cut feels nothing like it, Ill change the fuel filter out just so that i know its a new one, , I only have one ground that is going to the engine but I'll check it, I have no boost leaks, vacuum lines haven't fallen off and the nut didn't back off to adjust it's self so the pressure is still at about 39, I have checked the fuel pump wiring a couple of times and it all good, I've tries reseting the ecu a couple of time and it didn't help.

 

[TwoLiterLaser]

Word. So give your oil a smell and do a compression test.

 

[mikelv]

What are you using to log with? I see you use a translator for tuning, but what are your numbers? Is the car pulling timing, ect...

If you have replaced just about every part on the car as stated, then it's most likely in the tune.

Whenever I've had this problem, it was in the power transistor, or wiring for the ECU. If you have ever wired in an AFC, and things are "ghetto-spliced" back together in the wire harness, then you could have a bad connection to an ignition signal.

Also, if you soldered, you could have a cold joint.

In my case, what would happen is that certain RPM points throughout the range would give a little "pop". If you're getting a small "pop" then it's a bad signal causing small amounts of knock. If it's a huge "pop" and it's missing bad, then you got some serious counts of knock caused by a number of things including the tune.

Nine times out of ten, it's electrical either in wiring, or tuning.

If you don't have any logging devices, pull the plugs and see what they look like. Goldish brown = good, bright white = bad.

 

[cruisintalonawd]

I did a compression test and it is 90 to 95, i have never had an AFC the plugs ae a little black

 

[tqmx1]

Let's see, Casper Wy.= well above sea level = lower air pressure. Electricty is damm lazy it will always take the path of least reastance in other words if it takes less power to arc to ground than acrost the spark plug gapp well you can guess where its going.

Take a veary close look at the spark plug boots odds are you are going to find one with a nice little hole burned through it. With a lost spark systen with a bad wire insted of loosing one cylinder you loose 2

Change to a high quality plug wire set and odds are the problem will dissaper

 

[mikelv]

I did a compression test and it is 90 to 95, i have never had an AFC the plugs ae a little black

Black means rich. Most likely to happen when you lose spark. Re-check wire connections to the ECU, and to your Translator, coil pack, and transistor.

If you were knocking from a bad tune, you would be able to see real lean plugs, usually bright white.

What is your plug gap and boost level. You could have too large/small a gap and the boost is literally blowing out your spark.

Vacum lines should be ok since you're running rich.

 

[slowstang]

I did a compression test and it is 90 to 95, i have never had an AFC the plugs ae a little black

Shouldn't 9:1 be around 180psi per cylinder? I know he's well above sea level but it's not short that much air up there...

 

[TwoLiterLaser]

I did a compression test and it is 90 to 95, i have never had an AFC the plugs ae a little black

90 to 95 psi?

 

[mikelv]

Shouldn't 9:1 be around 180psi per cylinder? I know he's well above sea level but it's not short that much air up there...

No, he had to do a differential compression test, here is an example from another thread discussion I was involved with:


http://www.dsmtuners.com/forums/problem-diagnosis/325611-missfire-comes-goes.html

If not, then that compression number is not good.

I did a DIFFERENTIAL compression test. I am an Aircraft Maintenance Technician by trade and a differential compression test or a leak down test is what we use on piston aircraft engines and anything over 70/80 is good! The test is performed with a totaly different kind of gauge. The engine is placed on top dead center on the compression stroke of the piston you are testing. Then 80psi of air pressure is put into the cylinder and that is regulated by a regulator and is displayed on the first geuge so 80 is the reading on this gauge. The second gauge measures the amount of pressure actualy held in the cylinder and 78 or 77 is what was read on this gauge.

 

[TwoLiterLaser]

If he did a cylinder leakage/leakdown test then he should have referred to it as such. I am familiar with the procedure.

BUT he did say he did a compression test so I am gonna wait for him to confirm it was in fact a cylinder leakage test.

 

[cruisintalonawd]

Black means rich. Most likely to happen when you lose spark. Re-check wire connections to the ECU, and to your Translator, coil pack, and transistor.

If you were knocking from a bad tune, you would be able to see real lean plugs, usually bright white.

What is your plug gap and boost level. You could have too large/small a gap and the boost is literally blowing out your spark.

Vacum lines should be ok since you're running rich.

I have a M105 that never saw any knock, gap was 28 at the time with the 6's at 18 to 20 psi and switched to the 8's same gap after and it would only hit 15psi.

Shouldn't 9:1 be around 180psi per cylinder? I know he's well above sea level but it's not short that much air up there...

i have the stock 8.3

90 to 95 psi?

yes

 

[cruisintalonawd]

If he did a cylinder leakage/leakdown test then he should have reffered to it as such. I am familiar with the procedure.

BUT he did say he did a compression test so I am gonna wait for him to confirm it was in fact a cylinder leakage test.

i did a leak down test and at 40psi from the air compressor i could hear some air coming from the oil cap when i took it off, I had to get up close to it though

 

[TwoLiterLaser]

So on your COMPRESSION TEST you saw 90 to 95 psi of pressure in the cylinders?
And on your LEAKDOWN TEST, which you did at 40 psi, you heard air escaping from the oil cap?

 

[slowstang]

'Mods in profile" show 9.1 pistons. Anyway stock would be 7.8:1 and compression test should still be around 150psi.

 

[cruisintalonawd]

So on your COMPRESSION TEST you saw 90 to 95 psi of pressure in the cylinders?
And on your LEAKDOWN TEST, which you did at 40 psi, you heard air escaping from the oil cap?

Right and Right, i have to take the cap off and put my ear up to it but I'm sue if i have the pressure high it would have been louder

'Mods in profile" show 9.1 pistons. Anyway stock would be 7.8:1 and compression test should still be around 150psi.

that was the old engine i thought i deleted that, EDITING it now

 

[TwoLiterLaser]

If you did the compression test correctly you should be seeing upwards of 175psi. What does your oil smell like?

 

[cruisintalonawd]

What does your oil smell like?

oil and a slight hint of fuel

 

[TwoLiterLaser]

That is normal. I would be looking for a blown headgasket, skipped timing belt, anything that can cause your compression to be that low. If you have a timing light you can easily check the timing. Check and see if you have oil in your coolant.