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waycool
06-09-2014, 01:15 AM
I am trying to figure out the cause of my slight hesitation under hard acceleration sometimes. It feels as if the fuel is cut off every so often under acceleration. I have replaced my fuel pump and fuel filter about 15K ago, so I am thinking fuel regulator or injectors. Has anyone experienced this problem and what was the fix.

4thgenceli
06-09-2014, 03:06 PM
What motor do you have in your car? Have you checked your timing lately?

waycool
06-10-2014, 03:00 AM
1993 GTS with a 5SFE and 210K miles.

KoreanJoey
06-12-2014, 10:00 PM
Could be TPS as well.

Lonestag
06-12-2014, 10:09 PM
Here is a long shot, but it happened to me.

Do you have a metal cold air intake installed? If so, you might make sure that it isn't too close to the ignition wire leading into your distributor, I encountered a situation where a spark would arc from the wire to the intake when I first installed it.

waycool
06-13-2014, 02:26 AM
I will check these things this weekend. I am probably leaning towards the TPS. I think those things are pretty expensive from Toyota. Anybody run after ones?

sefiro
06-14-2014, 11:09 AM
I have the same problem. 91 GT 5SFE, 300K with a full rebuild 6 months ago. Just started diagnostics and am looking for answers as well. Thinks checked/replaced:
- distr/coil/plugs/igniter during rebuild
- Checked timing, injector ohms,
- found fuel pressure running at 50psi+ and will replace regulator this weekend.



Update:
- Replaced regulator, found maybe a 10% improvement
- During investigation on another poblem, found a very small tear on the hose from the EGR to the EGR modulator, Replaced and improved on hesitation problem some 50%
- Had also found the gasket between the EGR and manifold was missing. Replaced it and this eliminated the rest of the hesitation. The other rproblem I was invesitgating was higher than normal idle (not effected by EGR as it iis closed). I assume, that during idle, there was not enough vacuum to overcome the seal of the EGR metal to manifold metal. During higher rpms, when the EGR was open, the increased vacuum would draw some air through the seam and had random mixing for the intake on the cylinder.

MCcelica
06-21-2014, 10:05 PM
Also inspect the evap system soft lines. Make sure they have clamps and the hoses are in good shape. Under heavy throttle, the evap system dumps the extra evaporated fuel back into the intake. If there's a leak in those hoses, there won't be fuel in the evap system to dump back into the intake which causes a lean running condition. I don't believe OBD1 vehicles will trip an engine check light for that either. Hoses are also one of those things that are usually more often the culprit than something like a fuel pump, regulator, or injectors. Not only that, but they're cheaper and easier to replace. The other thing about hoses is that you're never going to hurt anything by replacing them.