misfire? power loss at 3200 rpm

[tommyturbo]

Got a valve adjustment and cam chain tensioners replaced today, the job Matt W did was excellent...and I enjoyed helping some and learning a thing or two. I know this is not related to anything he did, but figure maybe someone might have had a similar experience after doing such a job.

Car runs good except for one odd thing. it's a 95 atx.
I didn't notice this until after being on the fwy a while coming home, haven't noticed this in the past.

There is a weird dead spot at 3200 rpm +/-

Noticed when under load at fwy speed, in 4th, if you start to accelerate the converter unlocks and the car pulls nicely until about 3200 rpm, then it looses power, but if you increase throttle, it downshifts to third and pulls nicely.

I repeated this several times to be sure.

On the way home went to some quiet empty areas and did some tests.

From a dead stop in drive, it breaks the front tires loose and pulls nicely, power seems soft (but not as notice of a drop off) as it gets close to 3200 then it pulls nicely after that.

If you lock the shifter in 1st, it breaks the tires loose and pulls, I can't say I noticed the power drop off, or it was much more subtle. it always seems to feel strongest after 3200 rpms.

Now on a moderate throttle accleration, it seems fine, but when it
shifts to third it puts it right at about 3200 and it really feels noticable the lack of power.

When I got home I ran codes. Key on engine off, 111 system pass, no mem codes. Key on engine running, I get 225, knock sensor not detected. All my fords always throw that code when I do the engine running test...so I don't take it too seriously.

Any suggestions? It felt almost like a misfire at one point, but if it is it's very minor missfire.

I checked all the wires seemed tight on the plugs and at the coil pack.

Any advice?

 

[rubydist]

my first thought was the tps has a flat spot on it, which can lean out the car at that speed, which drops the power way down.

 

[tommyturbo]

TPS is very new, replaced it shortly after getting the car. A friend on shocal suggested checking for a vac leak.

 

[rubydist]

a vac leak should not be apparent at 3200 rpm, rather at idle.

even a new tps can be bad.

 

[tommyturbo]

Yes, I agree a new part could be bad. I replaced the tps about 6-8 months ago, when i got the car, as part of trouble shooting something with the trans.

So until yesterday before taking things apart there was no dead spot, it has only appeared since things were reassembled and the car driven.

 

[sdpatt]

Make sure the intake manifold runner control (IMRC) electrical connector and vacuum lines are connected properly. From an old post of mine:

"The routing of the secondary butterfly vacuum lines is from the center tap on the intake's rear plenum to the front (forward) tap of the black plastic accumulator tank [NOTE: the two "prongs on the accumulator tank should be oriented forward, towards the manifold, to properly engage the manifold mounting bracket]. From the rear tap of the accumulator to the bottom tap of the solenoid. From the top tap on the solenoid to the "T" fitting under the idle air control valve. From the side post of the "T" to the rear bank secondary vacuum diaphram valve and from the front post on the "T" to the front bank diaphram valve."

 

[SHOtimer]

Make sure the intake manifold runner control (IMRC) electrical connector and vacuum lines are connected properly. From an old post of mine:

"The routing of the secondary butterfly vacuum lines is from the center tap on the intake's rear plenum to the front (forward) tap of the black plastic accumulator tank [NOTE: the two "prongs on the accumulator tank should be oriented forward, towards the manifold, to properly engage the manifold mounting bracket]. From the rear tap of the accumulator to the bottom tap of the solenoid. From the top tap on the solenoid to the "T" fitting under the idle air control valve. From the side post of the "T" to the rear bank secondary vacuum diaphram valve and from the front post on the "T" to the front bank diaphram valve."

I was going to suggest the same. When your intake was reinstalled their must have been a problem.

Doug

 

[tommyturbo]

So went over the car today, it's been so cold at night after work that I have put it off.

The big hose from someplace in the valley that runs to the bottom side of the throttle body was on, but not pushed on as tight as t had been before, think it is for the crankcase ventilation? pushed that on tighter.

I also checked all the bolts that hold the intake down at lower manifold in the valley, some still were able to be tightened down a little bit more. only one that concerned me was the bolt closest to the pulley side of engine towards the front of the car. It seems to be tight but keeps turning, where as all the others reach a point where they don't.

Checked the plug wires to make sure they were all seated properly. checked over all the other vac lines and wiring. The one that caught my eye is the line from the purge solenoid to the throttle body. it was really cracked and dry-rotted. Replaced the vac line. the one down from the vapor canistor to the purge solenoid is pretty bad too, but it is a formed hose that changes diameter between fittings, so had to leave it alone for now.

Went out and drove the car, and it seems to be ok now. Wish it was a MTX because it would be much easier to get it under load at a set rpm, the atx is too downshift happy, but I got around that. I'll check back in this week after I drive it some more. Still is not setting any codes, all I get is 111 system pass. So as far as the computer is concerned it's very happy.

 

[rubydist]

if you put the shifter in "2" it will start and stay in second, so you don't have any downshifting issues to complicate your troubleshooting.

 

[tommyturbo]

Ok, I spoke too soon about this bug, it's still back.
This is a very soft feeling misfire / dead spot, feels very much like a soft rev limiter. It now has happened at 3200, 3000, 2900, 3500 rpms. From a dead stop it pulls fine, never feel any missfire in 1st or 2nd, usually overdrive under load and occassionally 3rd. It's not the torque converter unlocking, or locking.

Engine idles perfectly, so I do not believe it to be any type of vac leak....especially after going over them so much.

Car is not setting any codes, nothing in memory or in KOER tests. Car see's everything as being fine.

Sometimes it can pull through the dead spot, other times it just sits there, and if I increase the throttle too much it downshifts and pulls fine.

TPS was suggested, but I replaced that in april when I got the car, and can't see how it could fail so coincidently with doing the valve adjustment.

I'm open to any ideas anyone has, please. for those that don't know me I am sorta ocd, and these kind of things drive me nuts. For those that do know how **** I am about my cars you already get it.

Thanks!

 

[rubydist]

swap a known good tps to confirm whether its that.

 

[tommyturbo]

ok, will do.

 

[tommyturbo]

I went out to continue to trouble shoot the white atx, and the one bolt that holds down the manifold broke off, it felt loose so I started to tighten it, and all the sudden it broke off. It's the bolt that holds the manifold down by the runners, front most, closest to the pully side of the motor.

I changed the tps out, to one I have laying around, seemed to idle high, when I swapped the other back it idles normal now. If I spray carb cleaner around the runners that the bolt broke off, it seems to drop the rpm a little bit, but it's not consistent, doesn't happen each time.

Sprayed the cleaner around, the intake hose from mass air to throttle body, no changes.

 

[clayb226]

Car runs good except for one odd thing. it's a 95 atx.

Yes, I see your point, that is odd.

 

[jimtash]

Vacuum line to the IMRC? I have a Probe GT that has what's called a VRIS system which is similar in concept to the SHO with butterflies opening in the intake at certain RPMs. Car would have a flat spot at 3200 RPM when the butterflies open and it was especially apparent on a cold engine but went away as the motor heated up. The car felt like it lost half it's power. Turned out to be a dry rotted and brittle vacuum line attached to the solenoids that would soften from the engine heat and eventually seal. And it only showed itself when the vacuum was required to open the butterflies.

Either the lines that run to the IMRC on your car are not sealing, crimped by the intake somewhere, the solenoid itself is leaking, or the vacuum reservoir is leaking. The flat spot at a certain RPM is a dead giveaway that you have a vacuum leak somewhere that is controlled by a vacuum solenoid. It won't show itself until the system is used.

Not familiar about the EGR system but look to that as well. It's vacuum controlled and operates at a certain RPM. Anything that has a vacuum line running to it that opens or closes at a certain RPM is suspect.

 

[tommyturbo]

well, fixed the bolt, and replaced another dried out pcv line. drove home, seems to still do it occassionally. When It did it once I was able to watch and the rpm was about 3200 or so, felt sort of abrupt like a blast of wind hit the front of the car. rpms dropped to 3000 since I was able to see that much, but it pulled out of it. tried starting in second from dead stop through redline so the engine was under load, never does it then. driving around in drive, feels like it always happens around half throttle in higher gears, so went and bought a another new tps, drove home and still feel it, again about half throttle in drive, but pulls fine in 2nd from dead stops under load.

so checked codes, do both test, get same 111 system pass both ways, with the exception of the knock sensor code, and every one of my cars throws that on the engine running test.

After having gone over everything in the vac lines, manifold, tps, should I try swapping coil packs off one of the other cars? would think a bad coil pack would do that all the time, and not at such specific loads/rpms.

 

[SeanMc]

I wonder if it could be the VSS? ATX isn't really all that downshift happy, and with you saying it's downshifting a lot makes me think something is going on there.

 

[rubydist]

still no codes?

 

[tommyturbo]

vss is new, replaced right after I got the car. when I say downshift happy, the downshifts aren't inappropriate, just make it hard to repeat or force it to do for diagnosis. My bug seems to happen alot at fwy speeds, usually under load like climbing a hill. usually it's in 4th gear, the torque converter unlocks putting the rpms around 2800-2900 and as I accelerate it will usually pull in 4th with torque converter unlocked. As the rpms climb to 3200 rpm or so it has the dead spot, and will loose speed. If I continue to increase throttle, it will sometimes pull through it, or it will instead downshift to 3rd and pull fine.

Sometimes under load when it shifts from 2nd to 3rd if the rpms are around there it will do the same thing.

But if I start from a dead stop in second, which is putting a load on the engine, it pulls fine, no dead spots at all.

no erratic shifts. no delayed or too early shifts, no stumbles coming to a stop.

and still no codes

 

[SeanMc]

Then it's down to wiring, or back what someone else said, occasional dead spot on the TPS. All I can say is: have fun with that!