What to do next - misfire won't go

[hmwave]

Motor has been misfiring for over a month now and I can't find out why.

I tried gapping a new set of Denso IT20's at 34thou but it's still popping like crazy when off throttle and slowing down and generally running rough.

On WOT runs through 6K I can feel the motor holding back - the whole thing just feels like it's 'tired' and having a hard time making power. However it doesn't appear to be misfiring much under WOT. If I rev it freely it misfires lightly at 1500rpm, and at 5500rpm.

When I run at part throttle at constant speed in any gear I can hear and feel the misfire and it pops from the exhaust note more than ever before. Going down hills with no throttle the exhaust is popping like crazy and I can hear backfires.

I had my (trustworthy) dealer analyze it last week but they found nothing.
Relative compression results were within 2% of each other, no codes thrown, no signs of misfire on the analyzer. Physical compression check shows 150 on 1 and 2. However it's clearly not running right when driving.
Been driving this car for nearly four years now on a daily basis and something has definitely changed.

I just received my 44K oil analysis and Blackstone says the motor is looking fine with the analysis just where it should be.

Next step is to spray clean the MAF with Electronic Cleaner to see if that is the problem.

What could it be...
Dirty MAF, out of spec MAF
Bad sent of Denso's
Bad coil(s)
Need to gap at 32thou
Bad injector(s)
Bad air temp sensor or other sensor(s)
Fuel Rail Pressure Sensor going bad
Intermittent connection somewhere
Intake tract/blower somehow in bad shape
Other

Any ideas why this is happening and how to track down the problem are welcome - I'm getting tired of this.

 

[mustang john]

Mods ?

 

[SikGT]

You said you kept pulling plugs. Did they look good? Any signs of head gasket leakage? You said your oil is good too. Is the coolant lookin kinda clean? I had that same problem in my pick up and it turned out to be a leaky head gasket.

 

[YGETV8]

Try disconnecting your DPFE. Then try pulling the vacuum elbow off the top of the EGR actuator and plugging it (mine's got a broken off golf tee in it!). The second cured my cruise misfire issues.

 

[hmwave]

You said you kept pulling plugs. Did they look good? Any signs of head gasket leakage? You said your oil is good too. Is the coolant lookin kinda clean? I had that same problem in my pick up and it turned out to be a leaky head gasket.

Yes, plugs look great. Oil analysis suggests very little blowby and complete combusion - oil checked out fine at 42K miles (3000 miles on Mobil 1). Coolant looks very green and clean and no obvious signs of head leakage.

From the other posts my POA is:

1. Plug EGR line, test drive, unplug DPFE, test drive
2. Check Alternator voltage on a scope
3. Check engine and computer grounds
4. COP dealer test, then maybe buy one and try swapping it around
5. Replace FRPS
6. Predator log FRP, MAF_V, various sensors

MAF has aready been sprayed with electrical cleaner so that's not it.

 

[blubyeu]

Yes, plugs look great. Oil analysis suggests very little blowby and complete combusion - oil checked out fine at 42K miles (3000 miles on Mobil 1). Coolant looks very green and clean and no obvious signs of head leakage.

From the other posts my POA is:

1. Plug EGR line, test drive, unplug DPFE, test drive
2. Check Alternator voltage on a scope
3. Check engine and computer grounds
4. COP dealer test, then maybe buy one and try swapping it around
5. Replace FRPS
6. Predator log FRP, MAF_V, various sensors

MAF has aready been sprayed with electrical cleaner so that's not it.

My vote is COP...

 

[cobra04white]

mine was doing the same thing awhile back, thought it was cop so i rotated a new one around , but No! Did some data logging and there was no MAF reading. Got a new one from Ford, still a misfire. turned out it was my MAF extender!

 

[SVTCobra03_CA]

Engine Stutter

Hello,

I have a similar problem as described above with my 03 Cobra. The engine started to stutter like hitting the rev limitor on the race track after coming out of a 90 degree turn after a long straight. After waiting for 30 seconds, the car worked fine again.

However, today I had the same issue on the highway when shifting into 5th gear. When slowing down to 2500 rpms, nothing strange was noticable.

Any suggestions where I should start looking? I have a 2.2 KB with 11psi, Steeda CAI, KB trottle body, KB boost a pump.

Thank you for your help.

 

[gmynko]

Hows your FRP under throttle or at high revs?

 

[RKANYZ]

the ford dealer should have a diag tool called WDS or the newer IDS. they both have have a cylinder balance test feature. I'd go down there and ask them to perform this test to narrow down which cylinder is misfiring to help narrow down your problem cylinder. if you're out of warranty they should only charge you 1/2 to 1 hour of labor.

 

[vr4]

considering they did reletave compression i would bet they did the power balance too. its done on the same tool. they could also do injector flow test (easy on WDS, PITA on IDS due to needing to have the VMM and all the extra wires for it)


how is the fuel pressure at the rail under load? could be a dirty fuel filter.

this will definately cause a lack of power on accel and lean conditions on decel usually cause the popping.

 

[hmwave]

--------------------------------------------------------------------------------

Still haven't found the misfire root cause yet.

Thus far...

Dealer tested with engine analyer - no codes - all normal - relative compression within 2% all cylinders.
Physical compression check on 1 and 2 was 150psi.

EGR line pulled and plugged - ever so slightly less misfire - but not gone completely.
Dealer tested the EGR with the computer and showed me it's working fine.
EGR line refitted.

Fuel filter replaced with new unit. No improvement.

FRPS replaced with new unit. No improvement.

Predator logged VPWR, all steady above 13V.

Predator logged FRP - steady at 39psi, light or full throttle.

Checked the grounds - all tight and presumably good.

The misfire is felt and heard at light throttle, low engine loads at 1600rpm in neutral or in gear at speed. However when the engine is loaded say driving up a hill at constant revs (even 1600rpm) or under light acceleration there is no misfire.

When the car is cold there is no misfire. Less than two minutes after starting from cold the occasional misfire begins so it appears to be heat related. Odd thing is if the motor is hot and I turn it off for five mins, then on again, the misfire takes another couple of minutes before it returns.

I purchased a new COP and am rotating that round the cylinders, seven more to go.
Dealer thinks it's one or more coils so here's hoping (I can't find anyone with a COP tester).

I'll refit my LM-1 and O2 into the welded bung with a new LM-1 O2 soon to test AFR.

I have a BAS that I'll fit to see if that helps.

I thought I'd throw in two new front O2's just for the hell of it but balked when they came up at $120 a piece! Not sure if it could be O2 related though.
(just spent $400 on the Ford redesigned tranny cover plate / release bearing slide so now having to save some pennies for a while!)

 

[hmwave]

--------------------------------------------------------------------------------

Still haven't found the misfire root cause yet.

Thus far...

Dealer tested with engine analyer - no codes - all normal - relative compression within 2% all cylinders.
Physical compression check on 1 and 2 was 150psi.

EGR line pulled and plugged - ever so slightly less misfire - but not gone completely.
Dealer tested the EGR with the computer and showed me it's working fine.
EGR line refitted.

Fuel filter replaced with new unit. No improvement.

FRPS replaced with new unit. No improvement.

Predator logged VPWR, all steady above 13V.

Predator logged FRP - steady at 39psi, light or full throttle.

Checked the grounds - all tight and presumably good.

The misfire is felt and heard at light throttle, low engine loads at 1600rpm in neutral or in gear at speed. However when the engine is loaded say driving up a hill at constant revs (even 1600rpm) or under light acceleration there is no misfire.

When the car is cold there is no misfire. Less than two minutes after starting from cold the occasional misfire begins so it appears to be heat related. Odd thing is if the motor is hot and I turn it off for five mins, then on again, the misfire takes another couple of minutes before it returns.

I purchased a new COP and am rotating that round the cylinders, seven more to go.
Dealer thinks it's one or more coils so here's hoping (I can't find anyone with a COP tester).

I'll refit my LM-1 and O2 into the welded bung with a new LM-1 O2 soon to test AFR.

I have a BAS that I'll fit to see if that helps.

I thought I'd throw in two new front O2's just for the hell of it but balked when they came up at $120 a piece! Not sure if it could be O2 related though.
(just spent $400 on the Ford redesigned tranny cover plate / release bearing slide so now having to save some pennies for a while!)

 

[4.6modular]

Try disconnecting your DPFE. Then try pulling the vacuum elbow off the top of the EGR actuator and plugging it (mine's got a broken off golf tee in it!). The second cured my cruise misfire issues.

What is the DPFE????

 

[0mineralgrey3]

i'm having a VERY similar problem. Hope to see the problem solved. I have a slight misfire at idle and low rpms. On a full blast and under a load it runs smooth.

 

[hmwave]

What is the DPFE????

Differential Pressure Fuel EGR - it controls the EGR system (Exhaust Gas Recirculation) to minimize noxious emissions.

 

[CHINI]

I have a miss at idle... My tuner said it does not affect anything though. Like it jumps from 800 rpms to 1000 and you can fell the rumble

 

[camaro killer]

misfire

I have an 04 c0bra, keep getting sevice engine light, when I check it it says multiple misfire first 1000 rpm"s can't make go away any idea's

 

[hmwave]

Been a long time since the last post on this. I never did find the cause of the misfire and still have it. Over the past few months it has become much worse.

I've noticed a distinctive, constant 'whistling' sound while sitting idling, a fairly quiet but clearly audible 'whhheeeeeeee' tone from the engine compartment.
When I lightly blip the throttle the whistle disappears for a split second and then quickly returns to the same constant tone.

A few weeks back I mistakenly gave the motor full boost for maybe three seconds in sixth before I realized. Immediately after the SES illuminated. I pulled the code and it indicated a small EGR system leak. I cleared the code and it hasn't returned.

Appears there's a vacuum or other leak somewhere.

Any advice for how to track down a vacuum leak, mechanics stethoscope, other?

--------------------------------------------------------------------------------

Still haven't found the misfire root cause yet.

Thus far...

Dealer tested with engine analyer - no codes - all normal - relative compression within 2% all cylinders.
Physical compression check on 1 and 2 was 150psi.

EGR line pulled and plugged - ever so slightly less misfire - but not gone completely.
Dealer tested the EGR with the computer and showed me it's working fine.
EGR line refitted.

Fuel filter replaced with new unit. No improvement.

FRPS replaced with new unit. No improvement.

Predator logged VPWR, all steady above 13V.

Predator logged FRP - steady at 39psi, light or full throttle.

Checked the grounds - all tight and presumably good.

The misfire is felt and heard at light throttle, low engine loads at 1600rpm in neutral or in gear at speed. However when the engine is loaded say driving up a hill at constant revs (even 1600rpm) or under light acceleration there is no misfire.

When the car is cold there is no misfire. Less than two minutes after starting from cold the occasional misfire begins so it appears to be heat related. Odd thing is if the motor is hot and I turn it off for five mins, then on again, the misfire takes another couple of minutes before it returns.

I purchased a new COP and am rotating that round the cylinders, seven more to go.
Dealer thinks it's one or more coils so here's hoping (I can't find anyone with a COP tester).

I'll refit my LM-1 and O2 into the welded bung with a new LM-1 O2 soon to test AFR.

I have a BAS that I'll fit to see if that helps.

I thought I'd throw in two new front O2's just for the hell of it but balked when they came up at $120 a piece! Not sure if it could be O2 related though.
(just spent $400 on the Ford redesigned tranny cover plate / release bearing slide so now having to save some pennies for a while!)

 

[crazy8smokey]

Im Misfiring too please help

I’m having the same problem---but I put in 108 octane from Denver Co where the I’m from, but I bought the car from Al, where he had been running 100 and torco mix---Well come to find out that the gas I bought was leaded.. Great !
I’m draining the tank tonight and going to put 91 and maybe some octane boost..
Its misfiring at idle and when I get on it the MAF meter(SCT 2800) craps out

So kind of two problems, any help or ideas?
Because of this I haven’t been able to tune it for this attitude, until this is fixed

:??::shrug: