stumbling acceleration redux

[mytrplseven]

After chasing my tail for nearly a year over stumbling acceleration I finally found the problem. I had replaced the TPS, fixed the vacuum issues, replaced the fuel filter, rebuilt the AFM, rebuilt the injectors and tested the fuel delivery system for pressures and leak-down (all withing spec). Since the fuel line that was between the filter and the main feed line was cracked, I decided, since I was replacing it, I'd also check the fuel strainer for delivery restriction, and, since I was in there anyway, replace the fuel pump. Bottom line: the strainer wasn't an issue; it was the fuel pump. It made the pressures ok, but the fuel delivery rate was bad and the new pump solved the issue. Now I can go to redline without a hiccup. Yippee!

[Gawernator]

yay

[mikepellegrini]

Good job! Congrats.

[gtroth]

Did you measure the fuel delivery per chance?
Just curious how far down it has to be to cause your symptom.

[mytrplseven]

Well, I'm still here chasing this issue. It's gotten progressively better with each thing I try. So far I've changed the TPS which had noticeable effects, installed NGK plugs (replaced the Bosch copper + plugs) and the plugs I pulled out were perfect. Re-checked the vacuum system for leaks, today replaced a reference sensor with a new one because the connector was old, broken and the female side was, too. I bought a new female connector and repaired the whole mess and installed the new ref sensor. Once again, a noticeable change but still a little hesitation on partial throttle. Next step is to replace the new ignition wire set with Beru wires. This car idles real smooth and at WOT goes to redline like a scalded cat.

[mytrplseven]

Replaced the AFM with a confirmed good unit. I got a set of Bosch wires with Beru connectors from a member. They checked out evenly with an ohm meter and were in excellent shape. When I pulled the wire (with great difficulty) from the coil pin on the existing cap it looked very corroded and there was what I would describe as arc welding slag all around the pin. This cap is new and without removing the wires I would never have considered there would be an issue underneath the rubber. Now: new Bosch cap, NGK plugs, wires that are WELL connected and initially, I still have the hesitation under "soft" acceleration. Idle and and WOT are normal. I'm going to pull the DME and see if the IRQ has been messed with by the PO and possibly look at going to position 2 to see if that changes. My thinking is that I'm running a bit lean under these conditions. I also have a shop near Pompano Beach that will take a ECU off the shelf to swap out to see if the problem is there.

[mytrplseven]

This discussion is also under post "I have a feeling". I didn't expect previous posts to come back but that's the way it goes. I appreciate any and all inputs on resolving this mystery. Thanks

[VirginiaF1]

Howdy..
Did we already suggest new Ign Coil, O2 sensor and air filter?

[mytrplseven]

Yep. Here's a review of all that I've replaced so far:
Coil
AFM
TPS
ignition system (wires, cap, rotor, plugs [NGK])
Rebuilt fuel injectors and new electrical connectors
Intake manifold gaskets
Vacuum system initial leaks fixed and tested 2 times afterward
Air Filter
O2 sensor
Fuel pump, filter, strainer, hose
Not to mention all the rubber engine seals, belts, rollers, clutch, etc.
Pulled the DME and checked for bad solder joints and cleaned all the major connectors (DME, TPS, AFM)
Ref sensors and repair of connectors on one ref sensor line (broken by PO and hidden under the connector bracket).

[rick13]

I had similar problems. It was my DME.

[Chunkerz]

Have you cleaned ALL of your grounds? I don't see them on your list. Dirty grounds can cause funky problems.

[VirginiaF1]

Originally Posted by mytrplseven

Yep.

Well, if the Grounds solution fails, anyone closeby that can trade DME's?

[mytrplseven]

I had posted a long time back for anyone in the area with 944's and even though I occasionally see one, none of them seem to use the site. I think they're all out at the beach or fishing. I have a company who overhauls ECU's on the other side of the state who said they'd be happy to pull one off the shelf to see if that's the issue. It's tough to take the time off right now since I'm baby sitting a 4 year old by myself for 3 weeks. I'll get back into that part of it around October. Other than the slight hesitation, the car runs great. I planned to pull the dash and replace it with one I've got stored away with no cracks and plan to do grounds and a few other things during that time. I guess I can use the time to detail the engine compartment. It needs it since the car was in New Mexico for 10 years before I bought it.