Surge at speed

[Jusjofok]

So I recently took a two hour trip with my NA 82 280ZX and it developed a surge in it about half way through the trip. It started as just a stutter running at 80 and progressively got worse, by the time I got to my destination it would barely maintain 60 up hills and buck when accelerating. I checked fuel filter and pump pressure and didn't find anything wrong, free flowing through the filter and had 34lbs running jumping to 40 when I open the throttle. On my return trip the car would maintain 80 but surge on the hills. Any ideas what would be causing this? My definition of a surge in this case is a slight drop in RPM (maybe 50-75 rpm) and a lack of power.

Help would be greatly appreciated.

Thanks

[Z Babe]

There are several things that come to my mind in pinpointing the problem, so it'd help if we narrowed them down. First off, did the car run just fine previously? If so, was any work or modifications done to it before it developed the problem?

[Jusjofok]

Z Babe, the car ran just fine previously and has had no recent modifications or work done to it.

I have been driving the car as normal since the trip when it started the surging and it seemed to be running ok except for a surge on occasion. Last night it started with the surging (more like cutting out) again and wouldn't rev over 3500. It would run up to 3500 and wouldn't take any more throttle after that, I could coax it up with very slight throttle increase but not more than 200 or 250 rpm. If I rev the engine in neutral or with the clutch down it revs to 5500 easily. I experimented a little by accelerating in 1st through 3rd and it won't rev past 3500, just stops pulling, no pops, no backfires, just stutters and stops pulling.

So what do you guys think?

Thanks

[sblake01]

My 810 once developed the same sympoms. I ended up being the connector on the water temperature sensor. It was cracked and the wire clip wasn't holding it solidly in place.

[Jusjofok]

I will give the connector a look-see. I know it is old and brittle.

Thanks!

[Jusjofok]

I eliminated a couple things yesterday, I pulled the exhaust down from the manifold and drove it thinking it was the catalytic converter, it still did the same thing. It has been getting a little worse too, now it won't run up past 2500. I could tell one thing with the exhaust off, when it reaches its limit the exhaust noise quits so I am thinking it is shutting spark off for some reason. I also pulled the AFM to take a look at it, it appears to be fine (didn't check as per FSM), I pulled the cover and it didn't have any corrosion at all. I checked the connector on the temperature sending unit, it looked fine.

Keep the ideas coming please!

[Z Babe]

Check the O2 sensor. How old are the plugs and wires? How old are the FIs?

[Jusjofok]

Problem Solved!!

I did a throttle chop when it cut out and pulled over and removed a plug, it showed extreme lean. I then checked fuel pressure again which was ok, checked volume and found it took 10 cycles of the key to get about half a 20oz bottle of fuel, took off fuel line behind the damper to eliminate it and still very little flow, removed pump and had a great siphoning effect from the pickup in the tank, replaced the fuel pump and all is well. I can now fill a 20oz bottle in a few cycles of the key and no more cutting out.

A note to self, always check volume as well as pressure.

Thanks for the help guys (and gals).

Justin