Help!! surging and cut at 4000 – 4200 RPM

[mshawari1]

Hi,

I’m facing this problem since I’ve replace the front and back oil sealing.
That’s required the engine to be out then installed again.

It idle very smooth and the power is good under WOT till it reaches 4000 - 4200 then its look like the switch is turned-off then it’s comes alive after the RPM goes down. During this hesitation I hear the back fire sound in the exhaust.

I’ve replace the MAF, Fuel Pump, TPS and ECU but that not solve the problem.

Any idea
What could be the problem?

 

[cribbj]

Are you getting a MIL and is the ECU throwing any codes?

Because it's started occurring since the engine was pulled & replaced, it's likely a short or a bad connection if it's wiring.

If it's on the fuel side, perhaps a fuel line was bent and isn't delivering enough fuel? Or there's another restriction in the fuel delivery?

I'd probably start at the crank & cam sensors to see if their leads still look OK, then would go over all the rest of the wiring looking for loose connectors or grounds that weren't reconnected.

Then I'd inspect all the fuel lines, and probably would change the fuel filter, and if I had spares, I might change the FPR and possibly the fuel pump. Before I went into the fuel system too far, though, I'd hook up a fuel pressure gauge and run it back into the cabin so I could watch the fuel pressure as I'm driving.

 

[mshawari1]

Thanks,
I'm will replace the crank sensor and check the wires there ​

 

[yodathespian87]

I am having the smae problem. Just bought the car so I don't know what the previous owner did to it. But mine is between 1800-2000. If you could keep us informed that would be great, Thanks.

 

[mshawari1]

The problem solved!!
I've replaced the crank sensor and find that the wires is naked before the plug… separating the wires by 0.5 cm space then it's Ok.
I believe that the 1800 -2000 problem have another solution…I don't remember what was the cause but I think sideshow could help in this.
​

 

[cribbj]

Good to hear it was a simple & cheap fix.

Congratulations!

 

[mshawari1]

Still have small problem!!

When I press the pedal to WOT from idle … it will take some time to build the rev till ~ 2000 RPM then its fine ?

 

[cribbj]

What about when you're in Park or Neutral, does it do the same thing, or only when you're driving it?

 

[Smitherz]

That's crazy. I was trying to troubleshoot a guys car earlier this year with the same problem. It was super annoying because it was intermittent and that RPM range is exactly the speed in which you want to cruise on the freeway! I know exactly what you are talking about. I brought a whole bunch of my spare parts over to a friends shop to try and help the customer out. I replaced the ECU, the AFM, some sensors, coils, ignitors, checked all the wires, repaired some coil wires that looked faulty on the harness, all sorts of stuff. NOTHING helped. I told the guy that from that point on confirming that other parts are working would take a WHOLE lot more time and money. I just asked he pay for our lunch and I said I would call him if I ever came across someone that had fixed that particular problem.

The owner of the shop swears he checked the fuel pressure at different RPM's on this particular car. I'm thinking I would swap out the fuel pump or at least start by swapping out the fuel circuit resister thing (plugs into the engine compartment harness somewhere) just to see if it helps. I just have a hard time thinking it's something else besides the pump or the pumps electrical system. It's super hard to tell if it's spark related or fuel to me on this particular car. On this car the wiring harness is really fatigued so I was tempted to want to replace his out with one of mine but that would take a long time and if it wasn't the cause that would suck.

I just couldn't troubleshoot anything else on the car without it taking half of a day. He did have original o2 sensors in the car. If it were my car I would swap them all out and see what happens. I think they burn out over time anyways so the car would surely run better IMO with new ones even if it didn't help the problem.

 

[mshawari1]

What about when you're in Park or Neutral, does it do the same thing, or only when you're driving it?

The same John

I think the wires in the loom get too hot till its dry out.
You could break some plastic that cover the wires.​

Smitherz,​

IMO changing the whole loom is good option.​

 

[Smitherz]

Yeap I offered to put in another loom I had for $400. It's pretty much what I narrowed it down to being at fault. The loom on his car was in HORRIBLE shape. I had taped up 3 cracks with exposed wires near the coils and you know there are a lot more around the whole engine. I'm glad he didn't take me up on the offer because it definitely isn't worth giving him one of my good looms and spending a ton of time swapping it in. But I would have done it to help him out. I would have offered him $500 for it but I know he bought it 3 years before for $7500.