Within the last week my car has experienced a sudden and massive decrease in driveability

ONLY for ADVANCED technical discussion about the 240sx!
stuff_drummer
Posts: 3
Joined: Tue Sep 03, 2019 2:16 pm
Car: '93 RB25DET S13

Within the last week my car has experienced a sudden and massive decrease in driveability

Postby stuff_drummer » Tue Sep 03, 2019 6:05 pm

So, info about the car: 93 S13 w/ Series 2 RB25DET, RS Enthalpy ECU, Z32 MAF. Everything else stock about the engine.

The engine has always run a little rich but it's never affected the performance of the car. I'd have the occasional single afterfire, but only if i took my foot *completely* off the throttle when shifting to accelerate. The car has also had an inconsistent idle, but never stalls or dies, it just surges about 500 rpms, settles back down, repeat repeat repeat.

Within the last week, the car has become completely undriveable. It began with a series of sputters if I got on the throttle too hard while accelerating. The idle became rough and somewhat "lopey" if that's a common term. You can probably imagine what I'm talking about- Brum-brum-brum-brum-brum. Still doesn't stall out or die at idle though (unless the RPMS fall to fast, say, if I get surprised by a red light and have to hit the clutch and the brake at the same time and just let the throttle drop). Over a matter of days, these symptoms increased to the point where the car will only accelerate if you do it gently. If you try and get on the throttle too hard it'll surge and seize like when someone isn't giving it enough gas. every surge is accompanied with black smoke. oddly, this only seems to happen consistently under heavy acceleration in first, second, or third gear. If I'm on a highway, and I can get up to cruising speed, the engine behaves fine. In fourth or fifth gear, I can go to WOT and the turbo will spool up, the car will accelerate smoothly.

I've also noticed a *severe* drop in MPG. I typically get between 10-12 mpg in the city and up to 16 highway. Now I'm down to 6-8 on average. The exhaust smells heavily of unburnt gasoline, even when it's puffing black smoke. Consistent with the sudden rich fuel conditions, i've opened up the engine and cleaned everything I can get to. The spark plugs were covered in black carbon (i think) so I cleaned them gently with a wire brush.I think that does it for the symptoms, but it's likely I'm forgetting a detail.

What I've done so far:
  • Cleaned the MAF with MAF cleaner spray. It's an ISR and i've heard they tend to crap out spectacularly and suddenly. I don't have access to a known good Z32 MAF to swap them out and check. The MAF is about five years old
  • removed and cleaned the AICV.
  • removed and cleaned the 02 sensor. I actually have another 02 sensor around here somewhere, but damned if I can find it!
  • removed, checked, and then for good measure insulated the Coilpacks. As noted, spark plugs were cleaned of deposits with a brush.
  • Ran a treatment into a vacuum hose to clean engine deposits utilizing the "sip sip sip sip choke sit drive until there's no white smoke for ten minutes" method. This did mitigate the frequency of the symptoms, and slightly improve performance, but city driving is still next to impossible.
  • For shits and giggles, I ran a compression test. All cylinders were between 150-135 except for cylinder three, which was about 125.
  • searched for vacuum leaks using the soap and water method. I didn't notice any bubbles or changes in engine performance.
So, for the moment, I'm stumped or otherwise lack the tools I need to make a further diagnosis. Any input you all can offer would be greatly appreciated!
Last edited by Rogue One on Wed Sep 04, 2019 8:16 am, edited 1 time in total.
Reason: Moved to correct Forum


stuff_drummer
Posts: 3
Joined: Tue Sep 03, 2019 2:16 pm
Car: '93 RB25DET S13

Re: Within the last week my car has experienced a sudden and massive decrease in driveability

Postby stuff_drummer » Wed Sep 04, 2019 11:34 am

Well, after getting everything cleaned and put back together, the hesitation and city driving issues have completely gone away.

I also noticed that the car was idling smoother and more consistently, so I went to close the hood and noticed a trickle of fuel coming from the bottom of my fuel filter (which I had removed to check for completion's sake). I stopped the car, tightened the hose clamp. The fuel is no longer trickling out the bottom but the car is definitely back to lowered performance from running too rich, and I'm just gonna start experiencing the dirty carbon buildup problems again in the future. I have a stock fuel pressure regulator with a Walbro 255. The only reasonable explanation I can think of is that too much fuel is flowing through the system and somehow being forced into the engine; when fuel was escaping from the bottom of my filter, the pressure was lowering a bit before even getting to the regulator...

I'm at a loss. Is there anything I can try that *doesn't* involve buying a 260 dollar FPR kit?

macgiver
Posts: 941
Joined: Wed Jul 04, 2007 10:21 am

Re: Within the last week my car has experienced a sudden and massive decrease in driveability

Postby macgiver » Wed Sep 04, 2019 12:08 pm

If you think lower fuel pressure may help - temporarily , or permanently ,should GO install an adjustable regulator that you can drop down and checkout performance -wise . Gotta be able to beat that 260 something dollar figure ??

stuff_drummer
Posts: 3
Joined: Tue Sep 03, 2019 2:16 pm
Car: '93 RB25DET S13

Re: Within the last week my car has experienced a sudden and massive decrease in driveability

Postby stuff_drummer » Wed Sep 04, 2019 5:55 pm

I'm a full time laborer in the united states of america, so *of course* I don't have 260 dollars to drop on a problem that didn't exist a week ago.

With that said, I did a bit more googling and read that if my FPR was working correctly, there should be no gasoline in the vacuum line between the FPR and the manifold. I pulled the vacuum line and sure enough, a couple drops of gasoline came spurting out...soooo....the diaphragm in the FPR is almost certainly bad.

I googled OEM FPRs, hoping they were cheaper than aftermarket adjustables, and they were....by about 20 bucks...which I still can't afford.

At this point I'm at wits end. I'm literally trying to engineer my own pressure relief valve to stick between the fuel delivery and fuel return lines. and then I remember I'm not a mechanic, and I'm not an engineer, and the only reason I'm able to work on cars at all is the phrase "Well i guess it makes sense if this does that."

I even briefly considered loosening the hose clamp again to allow the over-pressurized fuel to trickle out of the line, but I don't have the money to be wasting 93 octane like that and I'm also not in favor of looking like Ghost Rider when on my next trip to Kroger.

pardon the sarcasm and flippancy, but I'm so angry at my car right now.


Return to “240SX Technical Forum”