where -o- where did the horsepower go?

[Huntervf]

Ok, I've been helping Denny trouble shoot his 90 for quite a while now. Last week before doing the 60k I test drove his car and found it well down on power...after the 60k there was a marginal change but it's STILL down on power, and there's his stalling problem to boot. The car starts up alright, and it idles fine. But if you stab the gas it just sputters and dies. Also, it will die while running a KOER test...specifically it dies near the end of the test, shortly before the goose test. Here's what we've replaced/tested so far (and all of this checks out a-ok):

New plugs, wires and valve lash

MAF
IAB
TPS
ACT
FPR

If anyone can correctly identify all those acronyms then you'll win a free smiley thumbs up courtsey of me in a later post

The fuel filter is brand new, and the fuel pump checked out ok. Secondaries are opening exactly as they should. The only codes we had were IAB and MAF...there's a new IAB on there now and the MAF code disappeared. Just to be on the safe side we swapped in two other MAF's that were known to be good, and the car still had the same problems.

At this point I'm not sure where to proceed. We've checked all the obvious culprits, and there isn't much else to do without going out and buying new parts. I don't know what else could be wrong with the engine. At this point I'm thinking either plugged cats or maybe the car is a bit out of time. It has 163k and I'm sure the y-pipe is original, not sure if the timing belt is. It has a recent water pump, not sure if the belt was changed but if the plugs/wires are any indication then the timing belt is probably original. I could sure use some more opinions on this...nothing is worse than a SHO not reaching it's full potential, and I'd just like to help Denny get his SHO on track.

 

[noSHO]

Huntervf:


MAF
IAB
TPS
ACT
FPR

If anyone can correctly identify all those acronyms then you'll win a free smiley thumbs up courtsey of me in a later post

Mass Air Flow
Idle Air Bypass
Throttle Position Sensor
Air Charge Temperature (sensor ??? dunno about this one)
Fuel Pressure Regulator

I'd have to agree and say it sounds like plugged cats, BUT, you should check some other things, too. First thing I'd do is check to make sure the DIS has a proper ground. It's a simple check and it can cause all kinds of weird things to happen. Are you getting plenty of spark? It COULD be a timing belt problem, but I honestly don't think it is. I've heard of SHOs that have gone nearly 200k on the original timing belt. I think the only way you'd get that noticable of a power loss is if the belt had jumped a tooth or two. Any bottom end knock, or (loud) top end tapping kinds of noises? Have you checked for a vacuum leak anywhere else? Could you be more specific about what exactly "down on power" means? I'll bet that would help narrow things down a bit.

 

[sdpatt]

If it still has the original timing belt you have got to change that thing. It has probably stretched enough to have significant play in the spans between the crank and camshaft pulleys and between the two camshaft pulleys. Tightening up that slack for $33 would return a chunk of the lost power.

The stalling at throttle tip-in sounds like an engine control problem. More specifically a throttle position sensor symptom. I read that you replaced the sensor though. You didn't mention if there were any codes generated during the KOEO or KOER tests. Were there any?

Have you verified that the secondary butterflies are opening? Just unplug the secondary solenoid electrical connector while the engine is idling and the vacuum valves should actuate and rotate the shafts.

 

[Huntervf]

<strong>Originally posted by noSHO:

Mass Air Flow
Idle Air Bypass
Throttle Position Sensor
Air Charge Temperature (sensor ??? dunno about this one)
Fuel Pressure Regulator

</strong>You win Dave!
thumbs_u thumbs_u thumbs_u

To answer the follow up questions, there are no suspicious noises, pingings, thumps, clatters or rattles to speak of...the engine hums right along like a good 3.0 should at all rpms. There are no detectable vaccum leaks. Down on power means just that...roll on the throttle and the revs climb but not as fast as they should and the car just isn't pulling that hard. For example, yesterday I made a left turn. Halfway through the turn at 5 MPH I floored it...the tires should have lit up like a roman candle but nothing, not even a little chirp from the inside tire. If anything I'd say it feels like it's fighting to rev up.

To answer Scott...I too thought the TPS was suspect, but there were never any TPS codes and we swapped not one but two other TPS's that worked just fine on other SHO's, and still had the exact same result. As I said above, the only codes we got were for the MAF and IAB...the IAB was replaced at the 60k, and like the TPS we tried swapping in two other stock MAF's that worked fine on other cars, and nothing changed. There is no check engine light, and all the codes are clear.

Denny has a new timing belt, we didn't have time last week to get it done but I'm suspicious that a new belt may be on there since the water pump was replaced shortly before he bought it.

The secondaries are DEFINITELY working correctly, verified that first thing.

Cats? Timing? Other?

<small>[ March 17, 2002, 11:07 AM: Message edited by: Huntervf ]</small>

 

[luigisho]

Sorry to hear Denny's car still isn't running right. That really sucks. Def. check timing belt and bad cats are possible. These are labor intensive procedures. So first how about swapping out other engine mgmt.or ignition parts? DIS,coil pack and computer come to mind. Do you have good continuous fuel pressure from idle to wot?

 

[Huntervf]

Well, this just doesn't strike me as a computer or electrical problem. His DIS plugs are in REALLY bad shape though...ironically the module itself is fine though. Even with the bad plugs the connection is still tight, and it's definitely hitting on all cylinders. There are no drivability troubles, the car always starts right up and idles well. I'll consider those options though, thanks!

 

[Denny]

CHRIS! Thanks for the post !! My ethernet's been on the fritz since Thursday so I haven't had an oppurtunity to check here much or research info or parts.
And to Scott, no we never found any codes for the TPS! We've found codes for the ACT(most of the times), MAF(two times), lean condition (on about 3 occassions). Currently the computer is all fine at 11 for both Key On Engine Off and Cont Memory. Can't do the engine running test as it stalls.
Oh yeah, one of the first things I repaired (after doing oil change, air filter, fuel injector cleaner) that found some missing power was taking care of slack in my throttle linkage. My TB wasn't opening up that much, now it does. But the pedal is kinda heavy as well. Could that be doing anything?
I'd like to order a Ypipe, but I'm cringing about doing business with the SHOShop or still having to go through another source that sells SS Ypipes
Oh yeah! Good news, I found the info page I had with the previous owners name and phonenumber a couple of hours ago, I think I'll call him up about the belt issue and any other maintenance issues tomorrow, hope he's respondent

 

[Huntervf]

Definitely call the previous owner if you can! That could save us a lot of time if he just slapped a timing belt on recently.

As for y-pipes...if you have the cash order one from Performance plus. It's not a SS pipe, they make their own and the quality is outstanding. You can order it today and have it probably on wednesday. Any **** shop can install it, should only take a half hour or so. The Performance Plus pipe the best pipe available...high flow, stainless steel and it's a perfect fit. Of course it's also more expensive, but you get what you pay for IMO.

 

[Lance Cheney]

Hmmm. Timing belt replaced recently. Wonder if it's on wrong -- one tooth off on any one of the gears could cause it to run pretty poorly. And you can't really check now that it's spun.

Might want to pull that off, replace the timing belt (and CPS while you're there, if it's isn't brand spanking new), and see if that cures it. Labor intensive . The fact that you're getting smooth (well, sounds like) acceleration, even if it's not really good, seems to point to some kind of restriction in exhaust or intake. Cam timing could definitely do it.

So the TB is opening all the way now? (not like it really makes a difference whether it's 60% or 85% open, until you hit 3-4k RPMs, but a good thing to check)

-Lance

 

[SHOMEUP]

Hey i dont know alot but i did have this problem- it started fine and sometimes had a rough idle- but if i floored it or ne kind of moment with the throttle it would starve for fuel and die- also if i let it sit at idle it would stall- also i thought it was caused by bad gas but it wasnt...i noticed my maf tube came off- sucking in to much air and not enough fuel ratio mix- i almost promise u its ur MAF or something to mix fuel and air together just like u got the act code and MAF code- it all has to do with mixture for that to happen- its not timing...if timing was off the idle would be too...look into tps and the tubing where the maf is and the maf itself and the act sensor- its all linked to the mixture..and if ur mixture is off u will lose alot of power and osmetimes stalling if not all the time...hope this helps- let me know if it does...

 

[Denny]

Yeah but we've swapped out the MAF with good ones and it still stalls

 

[Huntervf]

Hey Denny....how 'bout we just go sans exhaust. Would be loud but that would definitely answer some question

 

[Denny]

**** yeah!

 

[pittsburghsho]

Mine had the stab the throttle and die problem last week. I replaced the fuel pump even though it checked fine and it has been great even since. The acceleration seems much smoother now and it starts a lot quicker. The fuel pump is really simple to install, it only took about an hour from raising it up on a jack to lowering it and making sure there were no leaks.

Max
92 sho 115000 miles stock

 

[Denny]

Really? My fuel pressure was right around 40psi when I checked it. Did you experience any other problems beside the stalling? Loss of power? Anything?

 

[Denny]

NOOOOOOOOOOOOOOO!
I just tried calling up the previous owner. . his number has been disconnected with "no further information available" This is not good, I'd hate to show up at his doorstep unexpectantly and bother him about his time with the car, but what else can I do?

 

[Denny]

Horsepower gone

 

[mhodzic]

It is possible that belt has been replaced, but there is also possibility that they didn't put it back on corectly. They might have missed a toot or two. Also replace your cats. With 163K there is 95% chance they are cloged up. Lets not forget with 163k your rings wear out and compression is decreesed. You might have a burned valve. I would save up and do a total rebuilt, that is what I did on mine. Mine had 100k and you wouldn't bolive how much carbon was on the valves and how bad were the valve seats. If you can't aford a complete rebuild, than do the top at least. Change head gaskets, do a head job, and you will think that you are driving a different car. Keep those SHO's running

 

[bmray21]

i would definetly check the cats, you mentioned it fights to rev up, i bet thats your main problem. hope everything works out

 

[Mike Kopstain]

I know you guys said that you already did the MAF, but this sounds identical to the problem we had on the 94 ATX. It had NO power, fought to rev, if you gave it gas it would stutter for a second and then it would rev, it had NO mid range power. We changed everything you listed AND the oxygen sensors and the thing was still horrible. We unplugged the MAf and BAM, it was like a new car. It pulled a 15.4 at the track with no MAF. I know you already went through this, but next time you guys get to play with Denny's car, just humor me.