• Welcome to the Contour Enthusiasts Group, the best resource for the Ford Contour and Mercury Mystique.

    You can register to join the community.

Full Oval 3L Over Revving?

J

jeromio

CEG'er
Joined
Mar 22, 2007
Messages
34
I've looked this over several times and I am certain I have accounted for all the openings in the intake. However, I have a very, very strange problem - possibly related to the IAC? The car idles a bit high. I'm currently running the stock SVT tune and it sits at 1200 RPM or so - not sure if that's normal since effectively the butterflies for the "secondaries" are open with this setup compared to what the ECM thinks it has. But the real problem is that when driven, it behaves as if the throttle is stuck. So, I drive along at 2K RPM or whatever, then stop, let off the gas, and the revs climb to 3K or so - just as if I never let off the gas pedal. It will sit there for a loong time at that RPM. If I load the motor, it will reduce the revs, but not all the way. If I let it sit, it will eventually come back to 1200 or so. But apparently only if I'm stopped. I coasted (in neutral) 2 miles at a very slow pace (20mph) and it stayed at 3K RPM. But every time I try to get out and open the hood to see what's up, it drops the revs. So, it seems like maybe there's something about the car being in motion?

Oh, and the throttle will also "stick" with the car in gear with clutch out - so if I accelerate, then let off, it does slow down, but it will drive itself at 2K RPM or so. Not good.

BTW, cruise control cable is not even hooked up (won't reach with current bracket). And I have the extra (linear) throttle return spring on there too - the accel pedal is actually fairly hard to press now. And EGR is connected. Headers installed in place of stock exhaust manifolds. All exhaust is hooked up and both pairs of O2 sensors are connected. I'm using a Taurus throttle body and upper intake (escape lower).

Apparently something is giving the motor more air than the throttle, but it is somehow linked to the throttle? Like I said, I've checked for vac. leaks, can't find any. I had one before, that I could hear, but I found it and plugged it (it was that lower hole in the accordion). I can't imagine that the IAC, even fully open, would let in enough air to get the motor to 3K RPM. This is a very annoying mystery...
 
It's not - the idle is at 1200RPM even w/ cable disconnected.

I can't find anything basic to explain the over-revving. I would however, love to discover some obvious, fixable issue. My last mystery issue turned out to be fouled plugs :shrug:. So I'm game for any kind of brain storming. Must be something I haven't thought of, right?


I think it's really odd that I can't seem to get it to do t his over-rev thing while the car is sitting.

Also, I looked at it again tonight and I think I can hear a sort of air whooshing sound near the EGR vacuum solenoid. Motor doesn't rev when I spray carb cleaner around there though. Could be that this noise is normal - I dunno.
 
Yeah - I just can't find any leaks. Plus, it'd have to be some kind of weird vac leak to ramp up and cause this stuck throttle effect, wouldn't it?

I really thought it was a stuck throttle butterfly at first. But that thing is really fluid - very clean (unlike the SVT one I removed which was really gunked up). And I added that extra spring - the thing really snaps closed now.

I've been reading over the EGR operation and I wonder if maybe the valve is opening and then sticking open or something. So I would get exhaust gases added into the intake, but that would be unmetered and would lean things out before it really caused a bump in RPM - yes?

It's very odd that if I load the engine, it settles it a bit. I drive along at 35mph or so, push in the clutch, RPM bumps to 3K, apply brakes and let out the clutch (introduce load), then it drops revs down, push in clutch (unload) and it goes up - but not as high - maybe 2500RPM.

Maybe I have the PCV connected wrong. My FSM doesn't have any kind of a tubing routing diagram anywhere. There are lots of lines (vent, vac, etc.) and I could easily have them crossed up. Anyone have any diagrams?
 
jeromio said:
Yeah - I just can't find any leaks. Plus, it'd have to be some kind of weird vac leak to ramp up and cause this stuck throttle effect, wouldn't it?

I really thought it was a stuck throttle butterfly at first. But that thing is really fluid - very clean (unlike the SVT one I removed which was really gunked up). And I added that extra spring - the thing really snaps closed now.

I've been reading over the EGR operation and I wonder if maybe the valve is opening and then sticking open or something. So I would get exhaust gases added into the intake, but that would be unmetered and would lean things out before it really caused a bump in RPM - yes?

It's very odd that if I load the engine, it settles it a bit. I drive along at 35mph or so, push in the clutch, RPM bumps to 3K, apply brakes and let out the clutch (introduce load), then it drops revs down, push in clutch (unload) and it goes up - but not as high - maybe 2500RPM.

Maybe I have the PCV connected wrong. My FSM doesn't have any kind of a tubing routing diagram anywhere. There are lots of lines (vent, vac, etc.) and I could easily have them crossed up. Anyone have any diagrams?
Click to expand...

Well there is the possibility of a bad IAC but it sounds to me like you've got too much air entering the engine. If youcan't find it up top then start checking your O-rings on your LIM/UIM.
 
i know this might be a stupid question but i dont know so why a full oval ?? What is meant by this, any info appreciated thank :)
 
My full oval port in my SE did this as well. From what I've learned you'll need a really really really good tuner to play with the throttle decay. I built a 2nd full port and put it in an SVT and it did the same damn thing!
 
what throttle body? 65mm svt or stock 3L. was it optimized? if the edges were knife edged thats where my problem was when i first started it up. the person i got my 65mm took to much off, looked ok at first glance but when you took it off and looked up at the blade with a light behind it there was a gap all around it except for like a inch.
 
Looks like vac leak may have been a factor. I re-did the EGR gaskets and the situation improved. It still floats a bit too long after you let off the throttle, but I suppose that could be attributed to stock SVT tune on the 3L. I also did an experiment and unhooked one of the vac lines off the intake - motor just doesn't really run at all. It tries to die, then I guess the pcm bumps the Idle valve and it jumps up to 3K, then back down - over and over. If I induce a slight "leak" by connecting a plug with a tiny slice in it, it's very similar, just not as dramatic. I can't explain why my issue was unique to driving vs. sitting still. But now it's fine, so, who cares.

BTW, I have a stock Taurus intake and unmodified Taurus TB. I'm using the SVT TB Bracket, modified to work with the intake (cut and weld).

(Fredd22, if you search this forum, you'll see that Full Oval 3L means non-contour 3L with a non-contour (usually Taurus) intake. This is in contrast to split port uses in stock contours and cougars.)
 
todras said:
My full oval port in my SE did this as well. From what I've learned you'll need a really really really good tuner to play with the throttle decay. I built a 2nd full port and put it in an SVT and it did the same damn thing!
Click to expand...

I honestly have not found one instance where that rpm float was actually a tune issue even with the stock 2.5L SVT code in it. It has always been due to vacuum issues or a combination of issues.
 
I thought I had it licked with new EGR gaskets. Nope. Motor is still over-revving. I've now taken all the intake pieces apart 3 times. Checked, re-checked. I cannot find a vacuum leak.

This surging is driving me crazy. It's fine half the time (which is why I thought I had fixed it). Then I'll stop at a light and the motor will start surging up to 4K RPM. I can't even come up with an explanation for it - which makes it hard to try and diagnose and fix. It would have to be one helluva vacuum leak to bump the motor up to 4K. And why intermittent?
 
Jeremoi, replace your EGR valve. It's sticking. I've had this same problem on a V6 and several V8 (4.6L) engines over the years and always that resolved it.

From reading your description I'd say your temporary improvement when replacing the EGR gasket were due to inadvertently jarring the valve itself, freeing it up a little.

I fought this problem as recently as last year on an older (1993) Crown Victoria I was using for my commute. Tried cleaning it with carb cleaner, which helped temporarily, and then just replaced the thing when it started to surge again. No problem since.
 
jeromio said:
I've looked this over several times and I am certain I have accounted for all the openings in the intake. However, I have a very, very strange problem - possibly related to the IAC? The car idles a bit high. I'm currently running the stock SVT tune and it sits at 1200 RPM or so - not sure if that's normal since effectively the butterflies for the "secondaries" are open with this setup compared to what the ECM thinks it has. But the real problem is that when driven, it behaves as if the throttle is stuck. So, I drive along at 2K RPM or whatever, then stop, let off the gas, and the revs climb to 3K or so - just as if I never let off the gas pedal. It will sit there for a loong time at that RPM. If I load the motor, it will reduce the revs, but not all the way. If I let it sit, it will eventually come back to 1200 or so. But apparently only if I'm stopped. I coasted (in neutral) 2 miles at a very slow pace (20mph) and it stayed at 3K RPM. But every time I try to get out and open the hood to see what's up, it drops the revs. So, it seems like maybe there's something about the car being in motion?

Oh, and the throttle will also "stick" with the car in gear with clutch out - so if I accelerate, then let off, it does slow down, but it will drive itself at 2K RPM or so. Not good.

BTW, cruise control cable is not even hooked up (won't reach with current bracket). And I have the extra (linear) throttle return spring on there too - the accel pedal is actually fairly hard to press now. And EGR is connected. Headers installed in place of stock exhaust manifolds. All exhaust is hooked up and both pairs of O2 sensors are connected. I'm using a Taurus throttle body and upper intake (escape lower).

Apparently something is giving the motor more air than the throttle, but it is somehow linked to the throttle? Like I said, I've checked for vac. leaks, can't find any. I had one before, that I could hear, but I found it and plugged it (it was that lower hole in the accordion). I can't imagine that the IAC, even fully open, would let in enough air to get the motor to 3K RPM. This is a very annoying mystery...
Click to expand...

You are leaking air big time! You probably screwed up the seal on the LIM to the heads. Start over there.

Also, your secondaries do not give more air on an ovalport if they are closed unless you opened them. The system still works like it was designed to work. Only one intake path is open when those butterflies are open despite the fact that the air can enter through both valves going into the head.

I have datalog proof from xcal2 datalogs showing the load increases in the low range when the IMRC remains operational versus being open. The system does work and still works well enough on a split-oval conversion.
 
JEDsContour said:
Jeremoi, replace your EGR valve. It's sticking. I've had this same problem on a V6 and several V8 (4.6L) engines over the years and always that resolved it.

From reading your description I'd say your temporary improvement when replacing the EGR gasket were due to inadvertently jarring the valve itself, freeing it up a little.

I fought this problem as recently as last year on an older (1993) Crown Victoria I was using for my commute. Tried cleaning it with carb cleaner, which helped temporarily, and then just replaced the thing when it started to surge again. No problem since.
Click to expand...

Hey, didn't read this when I posted but this is a good idea too. :)
 
Also the vac lines to the valve covers. See if the back one didn't touch the EGR pipe and burn a hole in it.
 
I'm going to order a new EGR valve. I need to verify which Taurus intake I have (I'm ignorant: someone here posted "plastic Taurus intake forsale", I bought it, never even asked what year - I assume 96-99).

BTW: I've checked all 12 intake gaskets and they're all good, all seated perfectly and all bolts were progressively tightened to torque spec per FSM.
 
So, rather than spend $60 on an EGR, I blocked it off. Seemed to fix the problem. Drove the car all day and it was mostly fine - idle was often a bit high, but no surging. Then I got in the car - maybe the 8th time that day - problem is back?! Crap. Stumped. Then I noticed that I had the A/C on. Weather had been mild all day, got hotter. Drove the car around without A/C and it was fine. Turn it on, and the problem crops up - not constantly, but about half the time.

SO! It's not EGR. It's the friggin IAC! Now I did extend my wires, but I soldered them, so it's not a bad connection. I think maybe I just have a bad unit. I'm gonna run the diags on it this weekend. Unfortunately, the IAC is even more pricey than EGR. However, I have the ones from my SVT intake and also the Escape unit, so perhaps one of those can be made to work.
 
You must log in or register to reply here.
Back
Top