Misfires and rough idle with 8 news coils and plugs

[GEN 3 SHO FAN]

My car recently starting doing misfires at idle which is a little rough too. The car will starts everytime and will idle at a stable 750 rpm.

The coils and plug are news (around 10k). I inspected all last week : plugs (NGK Iridium) and coils all seems goods. Rear wiring also seems good and I added some heat and electrical protection (EGR hose clothing). I replaced all coils with spare news to take no chance but I let plugs there because they pass visual inspection.

Cams are welded.
No code.
No fuel odor.
New cam position sensor and crank position sensor. Also, new battery, alt and fuel filter.
I switched the coil 8, no change.
I cleaned and switched the MAF, no change.
I unpluged the fuel pressure reg, seems better. Fuel pressure is at 32 psi at idle and 40 psi at max. (FPR vacuum line is ok.)
My throttle body have lot of crap in it but not sure is related.
3rd cat is deleted.

Can it be a bad plug with no visual prob or not gapped correctly (at 0.044) ?
Can it be a vacuum leakage ? (I haven't try to unplug the IAC, I will.)
Can a bad TPS plug does that kind things ? (It's a 96 and no recall seems to be made on this car...)

Any help will be appreciated, thanks

 

[stephen newberg]

There is a sensor for the air intake that tends to get dirty over time and will produce the sort of effect that you are indicating. Eventually it will not let the car start. IAC? I forget the name. You can try cleaning it, but it is fairly fragile, and not hugely expensive, so many people just replace it.

pax, smn

 

[GEN 3 SHO FAN]

AIT : air intake temp sensor maybe (plugged on the box) ? The plug of the TB also have a TSB but seems ok when checked it visually.

 

[stephen newberg]

The more I think about it the more I suspect it is IAC. Idle Air Control? That really sounds familiar to me, so I am pretty sure that is it. Though it would not surprise me that it does check the temp of the incoming air.

pax, smn

 

[GEN 3 SHO FAN]

Danm, just found an old reply from Paul Nimz saying that at idle the fuel pressure must be 39 lbs (I have 32 lbs) and without the regulator plugged, it will be 43 lbs (I have 40 lbs)

Someone can confirm these numbers ?

 

[E1]

Danm, just found an old reply from Paul Nimz saying that at idle the fuel pressure must be 39 lbs (I have 32 lbs) and without the regulator plugged, it will be 43 lbs (I have 40 lbs)

Someone can confirm these numbers ?

Yes. As soon as I saw your first post, I started to reply. Then I decided to actually read the thread, you know, to see if anybody actually posted the correct numbers already.
Sure enough, they were posted.

Yes. 39 at idle is how I remember it.

How old is your fuel filter?

 

[GEN 3 SHO FAN]

Fuel filter has around 10 000 miles. It can be a cheap repair which I can do...

 

[GEN 3 SHO FAN]

Normal pressure will be 39 psi at idle and 43 psi at max (or reg. unpluged). I tought the difference between the two will be higher...

Maybe we squized too much one of the fuel pump hoses when reinstalling it in the tank...

 

[GEN 3 SHO FAN]

Ok we changed the filter and the pressure stay at 39 psi without the regulator plugged... And we are able to see that the pump needs more than 5 "key on" to built this low pressure...

I inspected/cleaned the TPS plug, no change.

I changed the Intake Air Control valve and misfires still there.

Seems to be only the pump. Strange, the car will starts all the times...

 

[GEN 3 SHO FAN]

Ok, find a pump today on a 99 DOHC wagon with 91 k. The assembly isn't the same (isn't the same for each year by the way %?&) but the motor inside is very similar. I will try to put in mine.

I made searches on Rockauto site to find a matching fuel pump and I'm checking the spec for each year to see if my plan will do the job. So many differences between brand and years... I was a little confuse when I tryed to compare the years. Here what I found :

1996 (dohc) :
70-85 psi / 55-65 gph
72-116 psi / 37-41 gph
95-105 psi / 55-65 gph

1999 (dohc) :
105-115 psi / 45-55 gph
87-109 psi / 58-65 gph
80-90 psi / 40-50 gph

IIRC, all of these are above what we need : 43 psi and 31 gph ? Can it be better to put a higher than specs ones ?

Thanks,

 

[E1]

When I returned SHO R T S to a normally aspirated drivetrain I left the 255 LPH fuel pump in the tank. Car ran fine.

I would say it is OK to run a bigger capacity fuel pump and your fuel pressure regulator will just let the extra flow go back to the tank.

I was running a Walbro 255 LPH high pressure pump.

Car died from rust, not a too big fuel pump.

 

[GEN 3 SHO FAN]

Ok, thanks Eric, your knowledge is well apprecialed. Not sure but the pressure seems to rise up a little when we compare years (Tauruses 1996 to 2007).

I can't found precise answer here and on V8SHO but TCCA had it for DOHC motor :

idle : 38-40 psi
WOT : 48-50 psi

Edit : Some TCCA guys seem to had a close relative problem I have. I remarked that the problem seems heat related and will come sooner when motor is hot. As I understand, the low fuel pressure allowing the gas to boilling on the fuel rail which will give very bad motor behavior like trans is blowing up. Some call this "vapor lock"...

http://www.taurusclub.com/forum/82-...oes-down-time-time-fuel-pressure-issue-4.html

 

[E1]

The newer cars have a returnless system. Different animals.

 

[GEN 3 SHO FAN]

We change the pump yesterday... we checked the pressure after the repair.
The pressure stay as it was : 32 psi at idle, 40 psi with regulator unpluged.
Wondering about what causing this trouble of low pressure, I take the car to return at home.
I gave it gas 4000, 5000, 6000, 7000 rpm !! I rediscover my SHO !
It seems the fuel pump had a bug and isn't the trans is going away as some said. The bug caused a pressure drop when driving and will only happens when you press the pedal more than around the half...

But something kept my attention. Normal pressures on these cars are really :
32 psi at idle
40 psi at max.

Edit : I can also say that this bugged pump cause some motor stalls on stops and red lights during hot days (or night, during city driving). This happens only when the motor was hot.

Thanks guys for helping me in this quest that I try to resolve for more than a year.

 

[GEN 3 SHO FAN]

Finally, it appears that I had 2 probs at the same time.

After more than one year with a new pump and no more sudden fuel pressure drop, I'm still experiencing misfires at idle and during rpm under 2000. The car is sluggish at low rpm but ok at medium and high ones. In attempt to find the cause we measured the fuel pressure and it stays at 30 PSI at idle and 39 unpluged...

Seems to be a rich situation as all 8 spark plugs are black with a gas odor. Tryed to roll with the FPR unpluged, the misfires stay there. Tryed to run without EGR pluged (hand made gasket with no hole) as it can stuck open or closed but misfires stay. Also, the motor is a little bit too hot during low speed rides (probably too much gas burning into the motor). The car have also a bad gas mileage.

This summer we unbolted the Y pipe to repair it. It had a big hole all around the last O2 sensor which we completely repaired (a plate welded all around with a new socket, they are universals). After rebolting, we remarcked that a very small hole still on the top of the second cat (not visible at eyes). When unbolted, I checked the second cat and it seems that he still good (not broken and white interior).

1-Can it be other cause(s) of this rich condition ?
2-O2 sensors can going bad without throwing a code ? (Will they tend to create a rich or lean situation most of the time ?)
3-Can leaking injectors can cause these problems ? (On all 8...?)
4-When I checked my spark plugs, I didn't take time to clean them. Can it help to clean them as they are black ?



Parts already checked : FPR replaced, fuel pump replaced, fuel filter replaced, TPS, IAC, IAT, air filter ok, injectors cleaned, MAF replaced, 8 news coils, 8 almost new spark plugs and the last and not the least, no code.

Maybe it is the time for a new Y pipe but it's really expansive... Will try to unplug O2 sensor(s) before buying this.

Note: Retreiving the mineral wool under the protective plates of the cats will help prevent rust forming on the cats (good for the 3).

Thanks guys for your help,

 

[Qshiplvr]

Not sure if this is relavant to SHOs but on my other car (Mitsu Ralliart 4G69) my mechanic who scoped the car when idling rough told me I had a "lazy" O2 sensor. I guess it was not malfunctioning, technically, so didn't throw a code, but it was not running smoothly (idle rough on startup and runs rich...black soot coating tailpipe). So bought 2 O2 sensors from Rock Auto on closeout, so hopefully installing them will solve the problem.

 

[GEN 3 SHO FAN]

Maybe... SHOZ123 wrote this some years ago :

"The primary(upstream) O2s are indeed necessary to run the engine in the proper closed loop A/F ratio of ~14.7."
https://shoforum.com/index.php?thre...nsors-wronng-cause-p0172.119484/#post-1320121

Maybe an upstream one is going crazy...(?) I never such a thing on that car however.

Yet another post from Nimz about O2 sensors going bad :

"Bank one is the one next to the firewall. HO2S1 is the first one before the cat. Look to see if the wire is melted or broken. Mine was rubbing on something and chafed. It is best seen from the passenger side wheel well after the tire and fender liner are removed."
https://shoforum.com/index.php?threads/p1131-error-code-plse-help.39382/#post-348445

References :

http://www.v8sho.com/SHO/TSB0197HO2SServiceTips.htm

Oh crap... In possibles causes it is said :
"HO2S Concerns:
· Contaminated HO2S sensor (contamination from the use of silicone-based cleaners and sealants, leaded fuel, excessive oil consumption, etc.)
· Deteriorating HO2S sensor"

Contamination by cleaners, I used like 3 sorts of cleaner to retreive carbon in the lower intake which was staying in place. I remember the motor made lot of smoke during some seconds after starting it...

 

[GEN 3 SHO FAN]

I was able to disconnect the upstream on bank 2 (front of motor beside A/C compressor) and after some rides, the motor seems to runs cooler and the idle speed is slower (750 rpm rather than 850). However misfires are always there...

I will go to my mechanic and unplug the ones near the hole (upstream and downstream on bank 1) and give it a try.

 

[3rdGenLover]

My car recently starting doing misfires at idle which is a little rough too. The car will starts everytime and will idle at a stable 750 rpm.

The coils and plug are news (around 10k). I inspected all last week : plugs (NGK Iridium) and coils all seems goods. Rear wiring also seems good and I added some heat and electrical protection (EGR hose clothing). I replaced all coils with spare news to take no chance but I let plugs there because they pass visual inspection.

Cams are welded.
No code.
No fuel odor.
New cam position sensor and crank position sensor. Also, new battery, alt and fuel filter.
I switched the coil 8, no change.
I cleaned and switched the MAF, no change.
I unpluged the fuel pressure reg, seems better. Fuel pressure is at 32 psi at idle and 40 psi at max. (FPR vacuum line is ok.)
My throttle body have lot of crap in it but not sure is related.
3rd cat is deleted.

Can it be a bad plug with no visual prob or not gapped correctly (at 0.044) ?
Can it be a vacuum leakage ? (I haven't try to unplug the IAC, I will.)
Can a bad TPS plug does that kind things ? (It's a 96 and no recall seems to be made on this car...)

Any help will be appreciated, thanks

Hello. This is my first post here. No long story, I love the SHO and I am a former Ford tech and current professional diesel tech.
Take this with a grain of salt. Just my 02 cents.
On any obd2 vehicle, the O2 sensors are critical for optimum running. Most folks believe that they do not do much except keep the govt. happy. ( Partially true) However, they also dictate many important running factors to the ECM. A lazy or contaminated sensor will cause a host of issues, seemingly minor but able to cause long-term issues as well. When you used the carb cleaner to get rid of some stubborn carbon deposits all that cleaner and residual gunk got "burned on" the the sensor tip. This will either cause false readings from the contamination or damage to the sensor tip causing the "lazy" effect of the readings from the sensors. Basically, a damaged sensor cannot keep up with the information moving across it. (The amount of air as compared to the amount of fuel moving across the tip)
Other than repairing or replacing the cat, all O2 sensors should be replaced.
Again, just my 02 cents worth. If this has already been read or is known by you, I mean no offense. I look forward to being around the forum.

 

[stephen newberg]

I am in agreement with the post just above. If there is anything dubious about your O2 sensors, the simplest thing to do is just replace them.

pax, smn