Todd Westphal

Cutting out under load

Stutters and hesitates at >75% throttle

-Initial fuel pressure after prime was around 42#.
-Jumped to approx. 56# after start.
-flucuate 2-3#'s while accelerating.
-would jump 5-6#'s while aggressively revving engine while cruising with clutch in.

Any suggestions?
My gut is thinking the fuel pump. Seems like a bit of work for guesswork.
2001 ws6 convertible with 29,xxx - Absolutely CANNOT do the trap door mod.

Thanks for reading.

LLLosingit

iTrader: (4)

Bad plugs or wires can cause a misfire under load.

Todd Westphal

Plugs didn't help, wires looked good.

Car is a garage queen, comes out maybe 1200-1500 miles per year.
Car may sit from time to time but what has my attention is I can put a fuel pressure gauge on the rail and see 0. I'll flip the key and it only comes up to 42#.
second cycle of the key will produce the expected 58# +/-. Is the low priming pressure indicative of a failing pump?

RevGTO

iTrader: (12)

Could be. In my case, I noticed on a scan that the car was going very lean at higher rpms. Fuel pressure revving unloaded was fine. So I put it on a dyno and sure enough, under load at higher rpm and greater throttle it started dropping off. The car ran normally around town but the pump was failing.

Todd Westphal

Thanks for the input REV.
I bought the car 3 years ago with 28,xxx miles completely stock. It was fairly peppy but not much different than the MazdSpeed3 I was daily driving for the 6 previous years.

After 2 years I decided to start working on a few bolt ons that could reversed down the road without affecting value or originality.
I bought the SLP flowpac, speed eng longtubes and had a canned tune on a new ECM burned by Frost and I am disappointed on how little the improvement has been.
Initially I had popped each of the main injector fuses under the hood (at different times) and the car would throw itself into limp mode while out for conservative drives.
After scratching my head several evenings I discovered that I had left the main buss of grounds loose (at the rear of drivers head) while removing the air pump.
Now the power comes on consistent and smooth until I really put the pedal down and then it shudders as it winds up the rpm's.

RevGTO

iTrader: (12)

Per my experience, I would say put it on a dyno with a fuel pressure gauge and datalogging. In my case, the fuel pressure started dropping off so dramatically after 4400rpm that they shut the car down. Datalogging will reveal any misfires or other issues as rpms increase in case the fuel pump is indeed maintaining pressure.

Todd Westphal

Ok. That's a difficult one right now as the car is garage bound for the next several months due to MN winters.
I can see where your going with having the gauge on it and being able to datalog simultaneously, but I would assume I would have seen the pressure drop off myself when I was hard on the throttle..
I don't think I had mentioned earlier that I did have the gauge rigged up and taped to the windshield while I was driving and performing my quasi testing.

RevGTO

iTrader: (12)

Oh okay. Well, yes that would amount to the same thing, especially if you have a tuning suite and can log during your runs. I just couldn't feel safe rigging a gauge up and trying to monitor it while going WOT on local highways.

I spent some coin putting it on the dyno, but ended up with results in print without putting anyone at risk.

ghardester

I know that you have mentioned the plugs and wires, and the wires looked good. And of course I assume that there are no codes stored. Maybe it is time for a new set of wires.

But that is not what I came to post. A bad coil can still supply enough spark for the car to run just fine, but not under a load. But you should get a trouble code from that. Something to consider.