ZPaul2Fresh8

I didn't read the WHOLE thread this time, but I've been keeping track of your problem over @ speeddensity.org.

I have a 93 also and to me it seems your TPS voltage is above normal @ .92v.

Mine @ idle is only .55-.57volts....

Hope you figure it out.

ZPaul2Fresh8

See you found the problem, goodluck with your new motor

Fastbird93

Thanks. Hopefully I'll be running again by the end of April with any luck. Should be pretty nasty.

I just have to ask, of all the reasons for a stumble, WHY did it have to be the worst??

mobleman

Great post!!
Quick question, did they identify what they suspect in causing the drop? i.e. rings, head gasket, valves etc...

Fastbird93

We're suspecting ring lands, as the block had 108K miles on it, with the last 24K being under be and driven very hard.

I'll give AP a call in another day and try to see where they are at. They're the one disassembling the engine.

If it helps at all, the shop that did the leakdown test could hear the air escaping through the pushrod passages it was so bad.

1FstFormulaV8

My problem is now fixed as well. The optical section of the Opti was cracked right down the middle. And I also had the CTS changed too.

blown383

Any updates?

-B

Fastbird93

Yeah. I've got a new shortblock and the same old stumble down low with the fast throttle movement. Car's down right now for a new opti (High Res Pulse code 36) and a heated O2 conversion.

blown383

So you're waiting for the new opti, o2 conversion and new bottom end?

-B

Fastbird93

No, new bottom end has been running for a few weeks now. I'm still sorting bugs out. I pulled the opti on it because what started as an intermintent DTC 36 turned into a persistant and constantly set code. The O2's I'm replacing because one looks to be on the fritz (sucks because it was only a few months old) and I get a bit of bouncing in and out of open loop at idle, so hopefully the heated O2 conversion will clean things up some.

I'm STILL getting that fuel load up condition though. Next thing to try on my list is unplugging one injector at a time.

I just replaced the fuel pump last week with a Racetronix and it didn't help.

wwarnke

sorry, but what is this??

techie36

Update!!

I just read this entire thread, my eyes hurt, but I'm intrigued...even though your motor wasn't the cause of the stumble, at least you got a 355 out of it

I have a slight stumble as well...haven't attempted to track it down yet...but it doesn't affect my driving, I'm the only one in the car who can notice it, passengers can't even tell if I tell them to pay attention right when it's about to do it.

Fastbird93

Well, I think this is what everyone was waiting for. I do believe that I have found and relieved the culprit parts of their duties.

A recap of what my issues were: Car was fine on a cold start up. After things started heating up, usually within 45 seconds, the car would mysteriously start running rich. Rich to the point of a fast deep neutral rev would cause the car to stall out at times. Under load while driving, the car was obviously surging, and whenever I got into the gas fast and deep, the car would misfire/stumble/hesitate for a second before picking up. On the dyno a once near perfect 13.0 A/F turned into a 10.5 at the low end and leaned out to a 13.0 at 6K RPM.

Parts that I had replaced or verified to be good:

Replaced: Opti, Coil, Plugs, Wires, Fuel Filter, Fuel Pump, Fuel Pressure Regulator, EGR, Oxygen Sensors, several revised tunes, and the SHORTBLOCK.
Verified to be operating within limits: Injectors, IAC, TPS, MAP, Evap System, IAT, ICM (off my other car), ECM (again off my other car).

Nothing did the trick.

So, back in July, while trying to set my valve lash, I was having a hell of a time getting it right. What I noticed at the time was that a bunch of my Comp R lifters were "spongy" at best, when warm. I could very easily compress the lifter by pushing on the back side of the rocker. I blew it off on the advice of some people who played it off as the Comp R's had a larger oiling port and thus bled down easier. I thought nothing more of it until after I replaced the fuel pump and the problem was still there. At that point, I only had a couple more options. Either there was an injector getting a fautly signal and sticking open (but I verified that I was NOT having a leaky injector), the lifters had something to do with it, or I had another fried shortblock. The most obvious choice was the lifters.

Thanks to TQdrivenWS6, I acquired a set of stock lifters about a month and a half ago. Having been frustrated with the car, and due to a minor setback while swapping the O2 system to the 4 Wire Heated units, work on the car was almost nil. So, a couple weeks ago, in went the new lifters, and finally last weekend I got to start working with Alvin, the Pcmforless chip guy, to get the car figured out and tuned in.

I IMMEDIATELY noticed a change in the cars idling behaviour with the stock lifters. On the same tune as previous with the Comp R's, the car was actualy surging at idle. Funny.....it never did that before. A testing idle rev where it used to stumble almost to the point of dying yeilded a tiny hesitation, which I am playing off to the plugs being fouled out. So today I took the car for it's first taste of the glorious asphalt since July. Driving it around, I noticed that my O2's were doing the rich-lean-rich-lean bounce instead of being pegged on the rich end. The car was surging, but it's still in the early stages of tuning. Then the time came, I was sitting in fourth gear at about 1500 RPM. Stab the gas, and the car just settled down and went. No stumble, no backfire, nothing but pulling from the start. Seems that my woes may be coming to an end.

So, it seems that the lifters were at fault. While cold, they were fine, I couldn't compress them at all. Aparrently what was happening was that as certain lifters warmed up, they were becoming "spongy" and not allowing the valves to open up far enough, causing all of my issues. Comp has already confirmed that if the stock lifters worked they'd work with me on getting a brand new set, even those that I currently have are over 1 1/2 year old (but with less than 900 miles on them).

Once we get the tune dialed in some more I will be without a doubt able to say that the lifters were the problem, but after the past weeks findings I am 99% sure that they were the problem. Many thanks go out to all the people that offered help along the way, and especially to TQdrivenWS6 who offered me the stock lifters in the first place. Thanks guys.

TQdrivenws6

Now you gotta get that thing tuned up, dyno it and get to the track!

Chris

Fastbird93

That is the plan. I'm still working on small details right now though. I've got a Y-Pipe that needs adjustment as it's hitting the bottom of the car, a persistent spark retard at heavier throttle loads (.5-1.5 degrees), and for some reason the car is showing rich at initial start up, but after about 10 minutes shows lean (which is think is more accurate of the two). Hopefully tuning will put the smack down on two of those issues.