SVX can't climb hills

[WhatIsThisIDont]

If there is a restriction in the exhaust, is there any way to pinpoint it?

[NiftySVX]

Not an easy way really, but unless someone stuffed something inside the system (don't laugh I have seen it) then it will be one or more of the catalysts.

If you are in a non rusty climate then you can attempt to remove them for a visual inspection, but I have been fooled by that before. Usually you can clearly tell if a cat is plugged. This isn't really that common on cars as new as the SVX but it happens.

Depending on your location, if the car is older than 96 you can cut them out, thought I personally have a moral objection to that.

In the process of testing, you can always take a video and post it. It would probably help us.

I am intrigued by your issue and am following it, I have not seen these symptoms on an SVX before. Engine performance concerns can be tricky, but logical diagnosis will find your problem. Best advice is to take a systematic approach.

As much information as you can give is best. The backfire problem you mentioned kills the low fuel pressure likelihood for me, but makes me think of a cam timing issue. BUT, the cam timing problem would be apparent always. Going up hills and under heavy load will stress all the systems, and as the fuel is richened the stress on the ignition system increases. This is why people are mentioning the coils. But I do not see how your coils could cause a backfire. It will also draw more fuel and shift the fuel in the tank which made me mention the tank sock (filter).

If you have an exhaust restriction, the vacuum will slowly decrease just before it starts running bad. The key is that the thing is running just fine and before engine speed slows down vacuum drops.

Sorry for the long post, I used to teach this stuff, and the best help I can offer is to try and "get you in the right mind".

[WhatIsThisIDont]

I have the gauge on it now. At cold start, it pulled 15 inHg steadily. As the idle fell, the vacuum went to 19 inHg where it holds very steady at idle.

When under revs around 2500, the vacuum goes to 22 inHg steady.

I let the car warm up under idle, and have been going between revs and idle for around an hour now. No difference from above.

I'll keep doing this for a bit longer. I can't really drive with it on the windshield because the hose I have isn't long enough. (Yes, the 9 year old me giggled at the end of that sentence too.)

Though we have another issue...

I connected to a small vac hose on top of the throttlebody area. The hose ran up from the plastic cover above the PCV valve. Went to pull
t from the nipple above, and it came off, but the rest of the hose came with it with a piece of nipple in the other end.

Joy.
I'm not sure if it was broken before and hanging there (judging by the previous owners handywork, I wouldn't doubt it) or if my combo of "grace and ease" and the cold did
It. Would anyone have any idea what that hose goes to?

I'll keep testing vac for a bit and update when I'm inside and can feel my toes again.

[WhatIsThisIDont]

So after another hour of idling and revving, there was no change. So I kept my new vacuum leak plugged with the gauge that I secured inside the engine bay and went for a drive.

I covered a few miles of parking lot, side street, and highway speed. At Wide Open Throttle, the car pulled very well with very smooth power.

I cut the test drive rather short because I don't want to get stuck somewhere in the dark and my shoes had soaked through, so I couldn't feel my toes.

After the drive, I checked the gauge again while at idle and while holding it steady around 2k. 19 inHg at idle steadily again and 22inHg steady at rev.

And with that, I am just about out of ideas.

[Tapani]

With something like EVOScan or Ecutuner you can have a look at what's really going on. EVOScan works fine with the interface from Mike.

Tapani

[dannmarr]

Originally Posted by WhatIsThisIDont

I am just about out of ideas.

Did you check the coils other than visually?

[Blacky]

Originally Posted by dannmarr

Did you check the coils other than visually?

My '92 misfired on long hills. It was a bad coil even though all of them looked fine. I wasted a lot of time before I figured it out.

[SVXRide]

Vac readings are spot on.

Still need to totally rule out the possibility of a Cat going bad --

Simple (probably overly so) check on the exhaust - are you getting what you'd normally see coming out of the tailpipes in the way of flow? Does the exhaust have a rotten egg smell? Is it black in color? I'd also go with OT's suggestion to remove the O2 sensors and check 2 things - 1. is the flow the same out of each port? (if it isn't, the one with the lower flow is going bad) 2. does the "lay down" still occur going up a hill? (if it doesn't, then you've got a bad main Cat)

If these final checks on the exhaust don't reveal a problem with the exhaust, then it's off to the next stage.

Here's a real "out on a limb" idea - a bad gas tank cap! If the cap is bad it won't vent correctly and will allow pressure to build up in the tank and effectively start choking off flow to the injectors. Simple test is to take the cap off and drive up your hill!

Fuel pressure/clogged injector (you already replaced your fuel filter, right?). A clogged injector(s) or bad FPR can hide at idle and under normal load, only to show up under load (going up a hill). At idle, disconnect one injector at a time to see if the idle changes (change = injector working). Assuming the injectors are fine (I'm going to guess they are given your SeaFoam treatment), the next thing to check is fuel pressure. I'm not a fan of just buying new parts until you replace the one with the problem, but this is a case where it's the easiest way to check this. The FPR is at the back end of the passenger side fuel rail. Is the vacuum line to it in good condition? If "yes", go ahead and buy a new FPR (better yet, swap in a known good one if you have one lying around) and install it. Make sure to put Vasoline on the o-ring when you install it to prevent a fuel leak. Go drive!


I'm still not 100% convinced there isn't a problem with one of your coils. You'll need a small blade screwdriver to help pop the connectors for the coils (they've got a small latch that you have to slide the screwdriver under to unlatch it). You'll notice I have given you a couple of other things to check before you get back to checking them!

Good luck.

Bill

[WhatIsThisIDont]

Originally Posted by SVXRide

Here's a real "out on a limb" idea - a bad gas tank cap! If the cap is bad it won't vent correctly and will allow pressure to build up in the tank and effectively start choking off flow to the injectors. Simple test is to take the cap off and drive up your hill!

Now that you mention it, the cap is very old and beaten, and every single time I fill up, I get quite a bit of pressure release. Every other car I have ever driven gives a little hiss when I open the cap, but the SVX always announces it presence in the gas station. Imagine the sound of the DeLorean door opening for the first time in Back to the Future. That exact sound, actually.

Fuel Filter had been recently changed, and I took a stethoscope to the injectors. Every one makes a nice, uniform clicking.

I'm about to go on a drive and watch the gauge when it dies. Wish me luck.

[SVXRide]

Originally Posted by WhatIsThisIDont

Now that you mention it, the cap is very old and beaten, and every single time I fill up, I get quite a bit of pressure release. Every other car I have ever driven gives a little hiss when I open the cap, but the SVX always announces it presence in the gas station. Imagine the sound of the DeLorean door opening for the first time in Back to the Future. That exact sound, actually.

Fuel Filter had been recently changed, and I took a stethoscope to the injectors. Every one makes a nice, uniform clicking.

I'm about to go on a drive and watch the gauge when it dies. Wish me luck.

Take the cap off before you drive out!!!

Bill

[WhatIsThisIDont]

I just got back from my drive. I put around 30 or 40 miles on it and got some interesting results.

I did the same test as the other night, and it ran beautifully through the test that brought it to it's knees the other day. Immediately after, I checked the vacuum gauge and everything was still spot on.

I then drove further out and back, making about an hour minute trip with a 15 minute break in the center of it. It went very well to my dismay until the very last hill before my parking lot when I womped on it and it fell on it's face for a second but recovered. I took it for another few miles and by the time I made it back, it was coughing and bogging down with any sharp throttle increases until the revs made it above 2k, at which point it was ok.

So I pulled into the lot and checked the vacuum gauge. It read 19 inHg the other night at idle. This time, it read 18 inHg steadily, but when I rev'd it, instead of holding around 22 inHg, it fell to 15 or 16 inHg and slowly worked its way back to 18.

I killed the ignition for about a minute to unscrew the gas cap. When I started it up again, it still wasn't happy, but it was back to normal after another minute of idling.


So I have a hypothesis.

Because this problem only shows up after a good bit of driving and beating, and then vanishes as quickly as it came once I shut it off, I'm not thinking an ignition issue. I'm not ruling it out, either.

I'm thinking that my main cat is partially clogged, creating a little pressure between the heads and cat. After enough running, the pressure builds to the point of choking performance. Once I shut it off, the pressure continues to slowly vent though the cat, making everything ok for when I start it a few moments later.

This would be the single weirdest failure I've ever heard of, and part of me wants to go have myself checked for hallucinogens for just thinking that, but does it at least sound plausible?

[SVXRide]

Yes.

You still need to do the drive with the gas cap off from the start to eliminate a pressure build up in the tank being the cause of a fuel starvation issue.

Cats don't "heal" themselves between drives. Have you done the exhaust related checks I suggested in my last post? I realize it's going to be a pain to get under the car in this weather

Cheers,
Bill

[THE NEW GUY]

we all know about the hesitation of stock svx to softly overcome the car's inertia. This hesitation is present only until 2500rpm's aprox. I fixed it by replacing the O2 sensors, knock sensors, the air filter (K&N), and resoldering MAF sensor. I'm not sure witch of those was the real problem but my Blueray does not have that problem anymore. (And my gas cap makes the same noise you described)
Knock sensors works on a physical principle and have moving parts inside witch are subject to changes if you put the nose up like climbing a hill. Those are not expensive.
I do believe you have a chronic case of SVX hesitation. After the cat thing, try changing the knock sensors.

[WhatIsThisIDont]

Originally Posted by SVXRide

Cats don't "heal" themselves between drives. Have you done the exhaust related checks I suggested in my last post? I realize it's going to be a pain to get under the car in this weather

It was just a hypothesis that air still flows from head to tail pipe, but there is a restriction only partially blocking it, so pressure would build behind it and would be let out when the engine is off, leaving the pressure to vent through whatever the partial block is. If the cat is dead, she's dead, and no amount of voodoo is bringing it back. I wouldn't even try it lol.

I may have access to a garage this weekend, so I'll try that with the O2 sensors then. Are these ones usually stuck in pretty well?

I plan on taking a little trip with it with no gas cap at some point this weekend, so that'll be a thing.

On a positive note, whatever that little vacuum hose I broke may have been broken before I got to it, since I'm seeing no real difference in performance. It's still on the list though lol.

[gwynethh]

[QUOTE=

On a positive note, whatever that little vacuum hose I broke may have been broken before I got to it, since I'm seeing no real difference in performance. It's still on the list though lol.[/QUOTE]

So you have an existing broken connector for a vac hose of unknown service. Should this be eliminated as a (very unlikely) cause before digging into the cats/o2 sensors? Agree it doesn't seem likely but it is a defect staring you in the face that can be struck off the list rather easily.