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Wavering and stalling in 240 turbo...


Guest Anonymous

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Guest Anonymous

Hey all,

 

Having recently finished the install of an 83 280ZXT motor into my 72 240, a couple of things are driving me nuts:

 

First, problem is stalling. On throttle, it runs great. It does not hesitate and seems to pull through the gears with authority. As I coast to a stop, however, the idle starts to fluctuate between 400 and 1300 RPM and eventually stalls out. The ECU is for an automatic (still not sure if this makes a difference). I have the original (unbaffled) tank in the car, but this is happening even with a full tank.

 

Second, my gas mileage is horrible! Literally between 8 and 10 MPG. Less if I'm reall getting on it. I checked the barn door on the airflow meter, and it seems to be springing normally. I'm completely puzzled. Please help!

 

Thanks,

 

John

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Been a while since I read up on that stuff, but off hand it sounds like maybe the BCDD (boost controlled deceleration device) it is a valve under the trottle body that allows more air to enter the intake during deceleration. Can't help you with the mileage problem. 8mpg is terrible, did you check for leaks?

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It must be running extremely rich. There is no BCDD on a turbo, so don't bother looking for that. Check your fuel pressure - I've had a pressure regulator go out that exhibited similar symptoms. Make sure the head temp sensor is working properly and verify all sensor connectors and ignition timing.

 

It's also possible you have a bad injector or two - they could be sticking open. Once you get a fuel pressure gauge on the rail, check to see if proper fuel pressure is maintained when the pump goes off with the ignition.

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Guest Anonymous

Thanks for the input guys. Mull this one over for a minute. The guy at the shop says that wavering and the gas mileage problem is because it does not have a speed sensor. Evidently the 72 speedo does to provide feed back to the ECU therefore, it has no idea how fast or slow I am going. Hmmm. Can anyone at least confirm this in theory?

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I have one word for the speed sensor theory - nope.

The speed sensor is used only for the cruise control. I originally hooked it up (it's not too hard to install it in the speedo), then I ripped it out, and no difference. I know of several people who have done the turbo/stock electronic installs - none of them installed the ss.

 

If you haven't verified you have good plug wires, cap, rotor, plugs, make sure of that first. The AFM connections should be clean, and check the FSM for the procedure on verifying the proper operation of the oxygen sensor.

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I'm not that up on the FI electronics but when I read your post...the first thing I thought of is that your engine is not adjusting itself for less air on a deceleration: it does fine from idle & acceleration but isnt adjusting fuel (as in lesser fuel requirement) on a deceleration.

 

Now, the question should be what does the symptom mean-too much fuel due to the FI system not adjusting for a decel or sticky injectors, bad pressure regulator?

 

Definately check the minor but most important things such as tune up items; cap, rotor, plugs & plugwires.

 

Just my .02's worth.

 

Kevin,

(Yea,Still an Inliner)

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Isn't there a cold start sensor as well? If that is staying open or closed or whatever (just reading that the engine is cold all the time), it could lead to both of the symptoms you are having. It's tough to diagnose via internet, but just another suggestion if you have already checked the other possibilities...

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Guest Anonymous

Wow, thanks for all of the input guys! I think that I have a bit of work to do. I checked the connector to the AFM and sure enough, it has a split in the boot on the motor side. Probably needs to be replaced. I also spoke to the mechanic that did the install on the motor and he said that when he pulled the AFM it was stuck open. Could be nothing, could be everything. My next move is to replace that AFM wiring. Looks like it could get complicated since the wires go into the main part of the loom, but heh, it's gotta get done.

 

SleeperZ,

I will also do a cap, rotor and plug wires as soon as I get back into town. And I'm sure that the plugs have fouled under the rich condition. I'll pull them too.

 

Kevin,

You describe the problem EXACTLY in the first paragraph of your post. And as I slow down, the only way I can get an even idle is after I slow to a stop (and the AFM is closed) is to rev the motor up to about 4K and slowly bring it down to idle.

 

Clint,

I'll check the vac line to the FPR as well. I know how crazy these cars can get with a vaccuum leak!

 

Tell ya what, as much as a PITA it is to have this baby stall out on decel, it sure does kick butt! Took her to the track last weekend and ran a 14.6 with a bad hole shot (2.055 60'). And that's with a 3.55 rear. My buddy with a 94 Vette decided that he wanted a piece of that 14.6 and he got wacked. Of course this time (on the street) I got a great hole shot, took 3 cars on him out of the hole, and beat him by a half car. Yes he definitely had the MPH on me, but he will think twice before he trash talks again.

 

Anyways, thanks for the input and I'll report back on the results.

 

John

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