1HZ Hesitation/Flatspot (1 Viewer)

[Sabbath]

Hey all. Got an issue with my 1HZ with an aftermarket turbo. 320,000km on the motor about 80,000km with the turbo fitted. Running 10psi non intercooled.


Issue being that for a while i've had a flat spot on acceleration in second gear, up around the 3000rpm mark like it's running out of fuel and then coming good.

Changed the fuel filter about 6 months ago and couldnt get the primer to pump up hard all the way, but it still started no problems but has had the issue still.

2 weeks ago i bought a new primer pump and i thought i'd fixed the issue for good. Primer pumped up nice and hard, and it started first turn with no long cranking like i'd been experiencing previously.

But about a day into having the new primer pump on there the issue resurfaced. Popped the bonnet to check there were no leaks and found that the bulb on top of the primer was soft and took 3 or 4 good pressed to get it back to hard, drove away and the issue was gone.


So my wonderings were - has anybody had a similar issue before and how was it resolved? And my brain has forgotten at the moment, but should the primer bulb be hard at all times except for right after you've let air into the system to change filter etc?

Thanks in advance

 

[roscoFJ73]

The primer pump only stays hard for a little while. I think the fuel lines typically have 2 psi in them when the engine is running. I would set up a temporary fuel supply under the bonnet and connect it directly to the pump. Wire the fuel can securely and go for a drive. If there is no problem ,you know its not a problem with the injection pump side of things.

 

[Sabbath]

Thanks for the reply, i dont drive the Cruiser that much so havent had a chance to do any proper testing on it yet.

The one thing i did notice is, last time i drove it it had about 1/4 of a tank and was doing the issue as above. Yesterday when i drove it i had to fill it up and the issue had gone.

 

[congocooper]

I’ve got a similar issue in second gear but at 2500 rpm. Only happens if I’m very light on the throttle; it doesn’t happen if I’ve got a heavy foot on the accelerator. I’m still interested if it’s something I need to attend to or not.

 

[mudgudgeon]

Almost certainly you have air getting sucked into the fuel lines.

Do some searching in this section. It's common and discussed a lot.

Typical culprits . . .
- Bad primer pump diaphragm. They crack. Replace primer/filter assembly
- Cracked fuel hose. Check all hoses from tank to engine
- Loose fuel hose. Old rubber goes hard. If fuel lines have been disconnected/reconnected, it's common for them to not reseal.
- Leaking fuel filter oring. Have you eventually charged the filter?
- worm drive style hose clamp deforming rubber fuel hose on a hose barb. Replace damaged hose, and use OEM style spring clamps.

All these can allow air to be sucked in WITHOUT any visible sign of a fuel leak.

Use clear pvc hose as adiagnosis tool by temporarily installing it in place of the last rubber hose just before the pump to see if you have air bubbles in the fuel.

 

[JDM Journeys]

Just to add to MG's sage advice above, the suction tube barb on top of the fuel tank is another place where air can creep in. It is metal and rusts over time... I started at the front and worked my way back replacing lines, chasing down startup smoke. Of course dropping the tank was the last thing I wanted to do, but it solved all my smoky starts.

But start with the clear hose at the IP.