MPG timing, fuel, and ??

[grantf]

So I have been trying to get better gas mileage in the last few days. So far I have done some easy things that needed to be done anyhow like a new spark plug wire set and rotor cap, an oil change, inspected and replaced a leaky vacuum hose and a timing adjustment. So far nothing has really improved engine performance with the exception of the timing, it was about 5 deg. advanced not to bad. I timed it back to the 10 deg. mark and the engine seems to run smoother no real power increase but it does run nice and has a stable idle. So next is to look at the spark plugs to see what they can tell me and I am thinking about bringing my injectors in to an injector shop for cleaning and service, Doctor Injector in Renton, the guy I talked to seemed very knowledgeable and quoted about $34.00 per injector plus 25 if the hoses needed replacing. MSA has a new set for $370.00. Any opinion for one over the other or a different solution for bad gas mileage. I had been getting about 10 mpg now I think maybe 12. I still have the odor of gas coming from the exhaust.

Edited June 7, 2011 by grantf

[FastWoman]

A set of Sorensen or Standard Ignition injectors should work fine. They're much cheaper. I'm running Standards on my Z.

[grantf]

where did You purchased them from?? Are you confident that the injectors are matched?

[Zed Head]

I'm using BWD injectors with no issues. Getting ~20-21 mpg avg. now. I got them at Schucks/O'Reilly. I got the cheap $40 ones, but now they have another BWD type for $77. Remanufactured. The remans cost $77, the new ones $40. So your $59 for cleaned and re-hosed is in the middle.

10 - 12 mpg is pretty low. Have you checked your fuel pressure and water temperature sensor resistance? Make sure you check fuel pressure with the engine running also to verify that the pressure drops with intake vacuum. My regulator went bad and mileage dropped to 15 mpg and the car really stunk. Are you actually calculating mileage or just guessing? At 10 mpg I would expect liquid gasoline to be dripping from your exhaust pipe.

[grantf]

Hmm.. Zed head that is food for thought, I have checked my fuel pressure after the filter it is good. Water temp sensor resistence I have not checked, How do I check that (thread link). You are correct in that my mpg is a guess, but it is really bad I am sure it is south of 15 mpg and my exuast really stinks of gas. what do you mean by the pressure dropping with intake vacuum?

[cozye]

You should be getting about 20mpg, if you aren't, its not running right.

I would not go the injector cleaning route. I did this, and it was a huge waste of money. Yes, they did a flow test and one of them flows better now, however I still have leaking injectors once they get hot (they said they fixed that, but they have no way to test if their leaking at 300 degrees. I've got a box of new injectors that are going on.

[FastWoman]

Also make sure your distributor's vacuum advance works. Take off the cap and rotor, and try to rotate the innards with your fingers. They will be under spring tension and should move smoothly. They should obviously also move if you apply vacuum to the vacuum advance fitting. You should get this to happen if you suck on the fitting really hard. The vacuum advance is poorly designed in these cars and prone to failure. You can get a rebuilt unit for around $100 at your local auto parts store, but supply is limited.

When your mileage is absolutely terrible, the most likely culprits are misfiring (usually ignition problems) and air/fuel ratio problems (most likely rich, but possibly also extremely lean). Dirty/old injectors don't usually cause bad mileage.

The best place to check your CTS resistance is at the ECU. Remove the passenger kick panel trim to expose the ECU. WITH YOUR IGNITION OFF, remove the ECU connector by flexing the little clip and pulling the connector straight off. (It's hinged on one end.) Then measure between contact #13 and ground. By doing it this way, you're also checking the integrity of the wiring and the connectors from the sensor to the ECU. Often the connector on the CTS is corroded and/or crumbled and does not make proper contact. This is true also of the thermotime switch connector next to it.

Edited June 8, 2011 by FastWoman

[grantf]

Hmm. I did try and check the vacuum advance, I sucked till my face turned blue and I saw nothing move. Should I see the "reluctor" move? By the way I have a zx distributor.

with my meter set at 2k I get .078 between 13 and ground is this normal?

Edited June 8, 2011 by grantf

[Zed Head]

You should see the reluctor move. The breaker plate, the plate that has the reluctor (or magnetic pickup coil) mounted on it, is the part that moves.

Another way to check it is to remove the screw that holds the vacuum advance module to the housing and slide the module out a little bit, pulling on the breaker plate, which is what the vacuum module does in operation. You will see the breaker plate move and can get a feel for how messed up it is. Don't move it too far or the bearings might fall out. It should move easily back and forth with no gritty feel. Look closely at the edges of the breaker plate for visible ball bearings. What happens is that the thin plastic locater for the bearings breaks and lets the bearings push out under the pressure of the breaker plate mounting assembly. Or maybe they get rusty and then the locater breaks. Either way, no more vacuum advance.

[grantf]

zed head, understood. I will look at this tomorrow. If I need a new vacuum advace napa sells a zx one for about 50 buckazoids. not to bad. keep you posted.

[cozye]

The best way to check your vacuum advance is to use a vacuum pump. I don't know that you could suck on it hard enough. If you want to get real technical, you should do it while the car is running, vacuum line plugged off, hook up mighty vac to distributor, and use a timing light to see how much vacuum advance you are getting. then with the vacuum advance all the way advanced, start to rev your motor and check the mechanical advance. You should be able to check your total advance this way and rule out any mechanical or vacuum advance issues. Keep in mind that your vacuum test on the advance might work fine, but the dashpot on the side of the distributor could be leaking or not working either which would cause your vacuum advance not to work.

If you are real careful, you can disassemble the advance mechanism, and clean it real well which will make it as good as new. I did this on mine, but it's tricky and I'd advise taking pictures because it's easy to get disoriented and not remember how to put the pieces back together.

[FastWoman]

Eric, I could suck on my vacuum advance hard enough to move it. It's not easy, though.

IMO the easiest and best way to check it is really just to give the whole assembly a twist with your fingers. It should move smoothly and not feel gritty, as Zed suggests. I think if you were just to actuate the thing under vacuum, you'd lose that tactile feedback and couldn't really determine whether it's starting to stick/jump.

$50 for a rebuilt dizzy is a good price, BTW!

Edited June 9, 2011 by FastWoman