Mechanics

SPARK PLUG GAP

1994 Geo Prizm

Engine Performance problem
1994 Geo Prizm 4 cyl Front Wheel Drive Automatic 118000 miles

Hi,

I asked a few questions about my car in the past. Thank you for the replies.

My problem is excessive fuel consumption. It is a 1.8L 7A-FE engine, A/T with o/d.

The car had failed emissions tests a few times in the past because of high NOx readings. But the last test it passed.

The Catalytic converter is relatively new, installed by the previous owner a year or two ago.

Spark plugs changed too.

A full tank of gas (13 gallons) lasts only for 200 miles with mostly city driving.

What I suspect is that incorrectly gapped spark plugs were installed by the previous owner.

Even NGK's official website says the spark plug gap for my car is 0.042 inch. Many auto parts stores do the same. Even Haynes manual says the gap should be 0.042. However when I look for a Toyota Corolla with the same 7A-FE engine it says the right spark plug is 0.032 inch. (BKR5EYA). I found out that the factory manual recommends BKR5EYA already gapped at 0.031 (instead of 0.032 of Toyota's) inch.

My question : Is it possible for spark plugs gapped wider than recommended to cause

a/ Emissions test failure based on high NOx readings,
b/ Excessive fuel consumption?

I bought NGK's BKR5EYA spark plug set and I will hopefully be able to install them. Can this correct these problems?

Thank you.
Avatar
BLUMONSTER
January 30, 2009.



You are only getting 15 mpg. You should be getting mid to high 20's in city.

Gap should be.032.

Are you noticing any black smoke out the exhaust?

Excessive gap can cause incomplete combustion, mileage will suffer. Plugs would be carbon covered.

I would install the new plugs and see if it helps, if not something else is going on (sensor malfunction, excessive fuel pressure, weak spark, leaking injector, ruptured FPR etc.).

Mmprince4000
Jan 31, 2009.
Thank you MMPrince for the reply.

There is no black smoke coming out of the exhaust. It is grayish whiteish smoke/vapor on cold days. But when I smell the exhaust it is strong.I smelled the exhaust of my wife's newer car but did not get the same strong smell there.

It is my first time trying to change spark plugs. And I failed even pulling out the wire. The first wire now has damage, I can see inside the black/gray wire (whiteish inner part).

I had to order new plug wire set but before that would it be dangerous if I just cover the damaged area (1/5th of an inch tear on the wire-black rubbery silicone part- closer to the boot) with electrical tape and drive like this before I install the new wires?

The extension I had turned out to be too short to reach the plug. So I have not been able to change the plugs today.

I am thinking of changing the wires and the plugs one by one, replacing the old wire and plug with the new wire and plug one at a time. Is this the right way of doing it?

Thanks again : )

Tiny
BLUMONSTER
Feb 1, 2009.
Replace the wires, do not try to repair, the ignition system creates significant voltage to fire the plug.

Change wires one at a time. Start with #1 closest to timing belt. Remove old plug and coat (dab) threads of new plug with Anti-Sieze.

These plugs use a crush washer as opposed to a tapered seat, DO NOT OVERTORQUE the plugs. Be carefull not to cross-thread the plugs. If plugs come out hard, get a thread chaser and clean the cylinder head plug threads up.

http://www.2carpros.com/how_to/how_to_change_my_spark_plugs.htm

Mmprince4000
Feb 2, 2009.
What size of socket and extension do I need to remove the plugs? I have 5/8 socket and 6 inch extension.I tried putting it on the plug but I do not feel any resistance to show that it is on the plug.I tried the socket on one of the new plugs and saw that it does fit. What am I doing wrong?

Also, how do I remove the wire from the distributer end? I see a clasp-like thing to fasten the wire there. How to remove it?

Thanks.

Tiny
BLUMONSTER
Feb 2, 2009.
A 5/8 should work, if not try smaller size (9/16), but the plug should be a 5/8. Next size up should be 11/16.

The wires should come off cap by squeezing them, they have alignment pins on the cap:


http://www.2carpros.com/forum/automotive_pictures/108325_cap1994_1.jpg



Use a longer extension if you have to.

Spark plugs have a stock number, like 2382, 7133, marked on box, which stock number do you have?

Mmprince4000
Feb 3, 2009.
Thanks for your reply/help mmprince,

I found out that the plugs were Bosch Platinum+4 type plugs.
I am adding pictures of old plugs here hoping that they are clear enough to produce a diagnosis. As far as I see there is no black deposits on the electrodes, but on the body of the plugs I see black stains/coating. Is that normal?

I had 3/4 full tank when I changed the plugs and wires, I filled up when the trip odometer indicated 203 miles or so and I calculated that with mixed city/highway driving the mileage came to be 22-23 MPG. But I drove longer distances on this tank than before. Also the weather was warmer most of the time.I am not sure if the change of plugs and wires were the only reasons for the improvement but I am happy. What do you think?

Tiny
BLUMONSTER
Feb 9, 2009.
I have to tell you I am not a fan of the multiple ground plugs like the +4.
I used them on a turbo engine once (14psi) and they would not fire past 6psi, while the single ground (even Bosch) worked fine.

I would check the condition of spark (blue), and the NGK wires are fine.

The +4's look carboned up and are mis-firing.

Look for gas in vaccuum line of FPR, you may have a ruptured diaphram.

The other issue is that if you do not properly torque the plugs, they will work loose, I check them (cold) after a couple of weeks.

That's a nice engine, wher did you get the headers?

Mmprince4000
Feb 10, 2009.
If the diaphragm is ruptured, would I need a new FPR?I am all for stock OEM replacement parts and I do not see OEM FPRs for sale anywhere.

I compared the previous pictures of the engine compartment I took of my car with the new ones and I see that I installed the wires the upside down and the shortest wire has a sharp angle with the boot. Is it OK if I leave it like that or should I change its position so that the wire sits straight? I do not want to play with it anymore to be honest. Unless I have to.

The previous owner installed the headers. Car has newer full polished stainless 2.25 inch exhaust from the engine back(4-1 header, flex pipe, high flow magnaflow cat, resonator, and magnaflow street muffler), new Bosch O2 sensor was also installed with the new exhaust by the previous owner. I would have preferred Denso or NGK oxygen sensor.I would have preferred newer stock exhaust.

Maybe because it failed emissions test and he thought it would solve the problem but from carfax report I see that it failed again so they sold the car to me without telling me anything about the 2 failed emissions tests.(Thank God, the state of WI changed its laws so that cars older than 1996 model eyar will not need emissions tests anymore.) The previous owner also told me that he used to get up to 46 MPG on freeways. What happened to the car that caused much lower mileage and fail emissions tests, I do not know.

Today I had a weird experience with the ABS. While climbing up the ramp out of a closed multi storey parking lot the blue ABS light came on, the yellow light went off. And I kept hearing click clicks coming from the modulator on the right side of the car and the brake pedal kept pulsating for a while, the yellow ABS light stayed off for longer than ever although my speed was 30 miles per hour. But eventually the dreaded yellow ABS light lit up again. : (

Can this be a good news to suggest that the sensor is not dead and the problem might be a slightly disconnected sensor or wires? I hope so. I hope it is not another sensor dying.

Thanks for your help, thanks for your informative replies MMPrince.

Tiny
BLUMONSTER
Feb 14, 2009.
2 and 1/4 inch primary tubes on a 1.8 liter engine?

46 mpg?

There is a practice in selling used cars called " puffing", " this car is a cream puff", " idles like a sewing machine".
But 46 MPG is a flat out lie, you should be happy with 30 mpg.

The exhaust may be a big portion of the problem, the large primary tubes cool the exhaust off so quickley that the O2 sensor may not be getting to operating temp, which is 600 degrees F. This will cause a rich condition.

The FPR should be available from NAPA or from Toyota.

The ABS system will have to be scanned at a local garage with proper equipment. It could be the wheel sensor or the ABS module.

The cylinders are 1-2-3-4 from the timing belt to the trans. Firing order should be listed on hood sticker.
Dist. Rotation SHOULD be counterclockwise (if unsure, rotate engine by hand with socket and ratchet on balancer bolt, rotate engine clockwise and note rotation direction of dist. Rotor).

Mmprince4000
Feb 15, 2009.