Fuel or Exhaust issue - not sure

[bhermes]

OK, a couple notes up front. My 76 is running pretty well. Starts great and seems to have decent power. I have a couple issues I would like to get a little direction on. I am new to the mechanic and restoration world but learning quickly. I have redone brakes completely (most if not all parts), upgraded to the 60 amp alternator and rewired for the internal voltage regulation, added horns and wired, added side marker lights that were missing, replaced internal door hardware, added new radio to name a few. All of these things I would not have been able to do without this forum / site. So thanks to all.

Ok to the issues at hand.

- I smell either a gas or exhaust smell primarily at high speeds (70-80 mph) during acceleration. I am leaning toward an exhaust leak but not sure and I am cocnerned maybe I should be running something different when it comes to the gas I use.

- At higher speeds (again 70-80 mph) when I let off the gas I get a pretty good kick back. I am sure there is a better term. Car runs good even at 90-100 mph as long as I am on the gas. Not bad otherwise but just want to get this thing compeltely dialed in.

- When coming to a stop and out of gear, the rpms will go to about 2000 until the car is almost stopped. If I leave in gear until the last second I can all but avoid the problem but still would like to get this resolved. Idles around 900-1000 rpms.

I know that this is alot for one post but just in case these items are related in some way.

[Wade Nelson]

Have a not-too-bright co-worker stuff a rag in the exhaust while idling on the rack/hoist and see if you can locate an exhaust leak.

Hint: He can hold it there longer wearing an asbestos or "oven mitt."

I'd be looking at a failed or misbehaving Throttle Position Sensor (or wiring) as possible cause of your high idle AND "kickback."

[bhermes]

Have plenty of not-to-bright co-workers. I am a high school teacher and we are having a pool party/red solo cup party at my house tomorrow. I will see if I can get one of them to volunteer.

Is there a way to confirm that the throttle position sensor is bad. I will check to see cost and maybe just replace anyway. Would this cause the car to idle badly. No problem at idle.

Thanks for the qucik reply.

[Zed Head]

Could be the BCDD. It's purpose is to cut fuel flow and reduce intake vacuum, through a throttle blade bypass channel, above 2800 RPM and 10 mph, under throttle closed deceleration. It's mounted under the throttle body and has a power wire connected. It's the weird looking thing with the rubber boot on it.

It's an emissions device so is described in the Emissions section of the FSM.

[bhermes]

OK, after reading a little on the BCDD, it appears to be common to disable the device. I would have thought it had a purpose.

Any thoughts or comments.

[grantf]

It could be both exhuast and fuel. Look at you're plugs. Are the black? As I am sure you know by now most S30s have the problem of exhaust leaking into the cabin. Do you find that there are more fumes when you drive with the window down?

[bhermes]

I am very seldom driving without the windows being down so will need to check this out. Just replaced the plugs about 1 month ago and the ones that came out I beleive were black but no telling how long they had been in the car. I will check out the new plugs. Grantf assuming you are heading in the right direction what are you thinking is the cause?

I am still trying to understand if disabling the BCDD is going to be acceptable. Also, should I be doing anything special with the gas I am using?

Thanks for the input.

[grantf]

I am not an expert on the BCDD. If you're plugs are black you are running rich. My car was running way rich in the past. It was so bad my rear bumper had black soot building up on it http://www.classiczcars.com/forums/thread42574.html.

Again it is common to smell exhaust in the cabin of S30s. If the window is rolled down at least part way the air flow actually causes exhaust to be drawn from the rear of the car into the cabin. I know this sounds counter intuitive. best course on that issue so far I have learned is to try to seal up any holes or caps in the body of the car including replacing worn weather stripping, tail light caskets and drain plug holes.

[bhermes]

OK, looking through this post and the one attached to grantf post I think I may be a little over my head on this one. Novice but learning and willing to learn more.

I think I will look at repalcing the BCDD and the throttle postion sensor.

In regards to running rich I believe that this is the case based on the spark plugs being black when I replaced them last. I also get a little black stuff (slightly wet) from my exhaust. Not sure really what to do here. Running with the windows down is a must, no air and 105F today. I read something about adusting the afm with a screw adjustment. Not sure if this will help.

Comments?

[grantf]

Why replace the TPS? if it is out of adjustment you can easly fix it. have you looked at the atlantic Z tech page? it helped out alot. http://atlanticz.ca/zclub/techtips/EFI&fuel.htm

If you are running rich and have some specific questions Fastwoman may drop a hint or two on this thread she helped out alot with my EFI issues.

Adjusting the AFM is tricky. If you are thinking about the idle inrichment screw, that will adjust the air fuel mostly at idle and not reallyu cause a rich condition. Again even when you do have youre mixture about right, you may still get fumes in the cabin. Try sealling up anything that would allow this. Also check the conditon of youre fuel hoses including the ones that go to the expantion tank in the rear of the car. Hope this helps. Grant

Edited June 29, 2012 by grantf

[bhermes]

I am looking at the TPS/AFM/ and BCDD to help alleviate my issues with rev when coming to a stop, out of gear, and the car kicking back some when I let off the gas at 70-100 mph. The tech page is great and I will at least look at adjusting the TPS if needed and it sounds like that the AFM adjustment will not really help. Car idles fine. I need to get under the car and check out exhaust and fuel hoses. I just do not really understand exhaust leaks and vacumm leaks etc.

[grantf]

Take things one step at a time. The Fuel injection system looks sort of confusing at first but as you start testing each component one at a time it becomes really quite simple. Do you have the EFI bible and the FSM downloaded yet? Some things that can cause an incorrect mixture are: Bad temp sensor, poor vacuum, AFM out of wack (in my case it was due to someone adjusting it incorrectly), poor fuel pressure, leaky vacuum hoses, torn boot between the AFM and throttle and bad or corroded electrical conections.

I would encourage testing components before replacing them, You may end up throwing money at a problem and not solving it. One simple test is the Water temp sensor all you really need is a multi meter and take readings at the ECU connector or if you want to be really accurate take out the sensor and suspend it in water on the stove using a thermometer you can see if the ohm readings are correct. Then you can move on to the next component.

Testing tools neaded:

multimeter (If you own a Z you need one anyhow)

vacuum gauge

fuel pressure gauge

timing light

In regards to the fumes try this: when you drive the car with the window rolled down and you start to smell the fumes :sick: roll up the window and see if they go away. If they do then it is exahst that is coming out of the tail pipe (normal) and entering into body leaks around the hatch tail light gaskets ect. If you are planing on painting youre car soon this would be the best time to remove the seals and gaskets and put new ones on.

Edited June 29, 2012 by grantf