mytrplseven

Some time back I posted about this issue and did all the stuff that was recommended by my peers. Here's the list:

New ignition system, new rubber seals throughout, vacuum system checked and sealed, new intake seals and air filter, rebuilt injectors, new belts, rollers, water pump, checked the FPR and FPD for fuel and noted none, New fuel filter, new clutch job w/new tranny seals, ref sensors checked and all correct, completely new brake system and SS lines. Also redid the AFM and checked /adjusted the operations of the door and contact strips for continuity.

Car runs and idles great, Shifts like gold, stops straight and true. It's a little hesitant until warmed up a bit.

When I romp on it, it feels like I've lost a cylinder and it bogs and stumbles a bit. I can get full red line if I need to (which I don't).

What now should I entertain/suspect as causes of this performance problem?

IGROWL

Did you try cleaning the grounds? It is farely easy and only costs you your time. Search Techno Duck and grounds and he has pictures of almost all of them for you and a diagram of where they are on the car.

I always say start with the free or inexpensive and easy items first and work your way to the expensive harder items.

JohnKoaWood

I see no mention of TPS check and adjustment, or throttle body rebuild.

mytrplseven

When I did the clutch job and AOS seal replacement I cleaned and reseated all the grounds I could find. I rebuilt the AFM and checked and adjusted the TPS. I plan to pull the DME and hit the solder joints and connector for continuity. After the engine has more miles on it, I'll pull the plugs and read them to see if it might be cylinder specific but the car runs great until I lay the pedal down. I'm wondering if the fuel supply might be restricted (as John in AZ mentioned) by the tank screen or fuel pump. I'm going to look deeper into that area and see if there's any tests I can do at WOT.

It's a process and the really hard work is behind me.

TexasRider

My first three thoughts on reading this were

1.) Be sure you are getting the full fuel flow and the fuel pressure up at the rail and injectors.

2.) Be sure the car is not leaning out as I just went through on a buddies of mine carbed car. We had to weld in a port in the exhaust and then wire in a air fuel meter to see it was leaning out badly - of course we could feel it.

3.) If that checks good then I would try different plugs and/or wires if they are not new and new plugs. I know Chris' 951 was having this and I was encouraging him to dump his and get the correct plugs. It helped.

mytrplseven

Tex: since I have new wires, plugs and rotor/cap, I'm suspecting a possible low fuel flow under demand of WOT but I can't find a way to test for it. There must be an accepted procedure for that somewhere. I may be looking at draining the tank, checking the screen and maybe replacing the fuel pump, but I'll do the 3 basic tests first to see if it even meets those parameters. My filter is new and car runs fine except WOT. It was doing this before I replaced all the stuff I replaced so I'm confident the problem doesn't lie within the ignition system.

TheHummel

I'm having extremely similar problems. At WOT at around 3000-4000rpm it will bog down and become hesitant... the distributor cap, wires, and plugs are brand new, and I've been up to date on all my other maintenance... I suspect its got something to do with the fuel system as you said. I'll be monitoring this thread.

944Ross

Sounds like an injector with a coil going out

Hollywood D

I'm going to say it's electrical related. Me thinks you are not getting good spark which is causing it to stumble.

mytrplseven

Surprise! I tried the easiest things first. I unplugged the O2 sensor and the car took off like a shot. It really moves like it should now. Now I have to decide if I even want to replace the darn thing since it runs so good.

TheHummel

Excellent. I will try this and see how it works on my car. Is your car using an aftermarket DME or anything of the sort? I would suspect that would make a difference, as it is a critical part in feeding info back to the DME. Right now its probably reverted back to a normal back up state so to speak. My car is oddly modified (was once a personal test car for the founder of a tuner company), so I don't know how it would react haha.

mytrplseven

Don't know just what the function of the O2 sensor is and haven't had the time to check. I've left the question on the website. My car, as far as I know is totally stock. The PO wasn't into that kind of thing. I'm just happy to have it running like it should.

Hollywood D

It has something to do with emissions. Not sure exactly what though.

944Ross

The O2 trims fuel feed as needed to keep the cat in proper operating range. If you are running without, it may burn up your cat pretty quickly. But other threads on here have me doubting that the DME really uses the O2 to the extent more modern cars do.

mytrplseven

Clarks Garage said that the O2 sensor is used while the car is cold to run a richer condition and then when up to proper temps the input leans the mixture to proper setting. Since my car was stumbling like it was fuel starved at WOT I'm assuming that the sensor was failed in the lean condition.
I've seen several posts where people have been running without the O2 sensor installed at all. I'm not sure if my cat will suffer any more than it has with the O2 sensor being defective for so long. My plan is to run the car on a short trip this weekend and then read the plugs. I'll replace the sensor with a new one if needed.

Ross, I bought the car in Santa Fe and drove it fearlessly to Florida.