I need help with my 1993 J30. Delayed acceleration

[zigaratt]

I just got a 1993 Infiniti J30 with only 50k miles on it. It has two problems. It has an exhaust leak, right before the muffler. I can fix this one easily. The other problem puzzles me. The car has a lag in acceleration. When I press the gas (I mean floor it), the car does not respond. After a second or two, the engine starts to rev up and car starts to accelerate at a much slower then normal pace. There is no check engine light. The bulbs are fine. I checked the ECU self-diagnostics. It gives me a 55 code, meaning that all systems are good. The engine sounds smooth. PLEASE HELP!

[Q45tech]

Check the fuel pressure against specifications 34>43 under acceleration.Probably needs new fuel pump and an injector rail flush.

[zigaratt]

Thank you for your reply. I have checked the fuel pressure by connecting a gauge between fuel filter and injector rail. The pressure is close to 40 psi at idle. When I disconnect the pressure regulator vacuum hose it goes up by about 5-7 psi . Also when the gas is pressed, the pressure also goes up. I have extra power transistor, and ECU. Connecting those did not improve the sluggish throttle response. I have some positive results by adjusting the throttle position sensor while keeping the idle speed at ~800 rpm. I adjusted up to the point just before opening the throttle switch. I also have an extra TPS. Throttle is better after adjustment, but not like my other cars. There are no codes. What can be the problem?

[DominickJ30]

How clean is the engine??

When is the last time you did a tune up? Plugs are NGK?

I would do a power balance test if you have access to a computer.

TPS should be set to .4-.5 volts at idle.

[zigaratt]

I have adjusted the TPS for .4 volts. I had NKG plugs with correct gaps. Just to check, I also tried BOSH platinum. Absolutely no change. Air ducts and throttles have been cleaned. No improvement. I took out the crank position sensor to see if the injectors click when I turn it. There was a paint mark to identify its position. From the records from the previous owner it showed that the crank position sensor was adjusted by a mechanic. He turned it all the way clockwise. So I grinded few mm more groove to turn the sensor even more clockwise. When I tried my acceleration, this time the engine revved up much rapidly. Throttle response is quicker. However, it is not yet like a sports car. I think, something is loose inside the crankshaft position sensor. Has anyone opened one and fixed it? If so please let me know how to fix it without destroying it.

[DominickJ30]

Well, the crank angle sensor controls ignition timing.

The only way to properly set it is to get a timing light. Connect it to the number one plug wire. And set timing to 14 BTC.

Should purr like a kitten.

Also setting the TPS a little higher, should provide a little better pep off the line, but Ive found that .488 volts is where I want mine at for smooth shifts and all around good performance, after all you dont redilne the car in every gear I would hope.

[metaverse3]

Check the Mass air flow sensor and clean all contacts. check the ground connection.. Tap the sensor while the engine is running to see if it hiccups...

Check the knock sensor... Check all grounding points..

[bullittandy]

Unless there is a mechanical problem with the throttle cable this sounds like a engine timing issue. If the crank angle sensor was changed then there is a very good chance this is the problem. If so then it must have code but I'm not confident of this only having mucked up the timing on older carbed cars where 10 degrees of timing makes all the difference.

Any chance a replacement floor mat is too thick? I only ask because this happened to me on my old Mustang Bullitt and it reduced my 0-60 from 5.5 to 8.0 seconds.

[IrishCream]

Im having the same exact problems with my J30. Delayed acceleration/high revving/late shifting. The only difference is my driveway is on a slope, so for the first minute I have all my power but after i stop at the first stop sign 1/2 mile down the road it all starts.

WHY IS IT DOING THIS ?? HOW DO I FIX IT ?? COST? Thank yo for your help!