sellis1552

I have a 94 ex coupe with the d16z6 vtec engine. When I first got the car, it had great acceleration and fuel economy, about 30mpg. Then everything went down hill. I lost fuel economy, power, and my exhaust got louder. About a week ago I did a full tune up (it really needed it). Anyways, I upgraded to NGK plugs, new fuel filter, oil change, and K&N air intake. For a couple days everything seemed great. It had all its power back, seemed quieter, and was getting 30mpg+. Now all the old problems are back.. lacking power, economy, and exhaust is loud. I'm thinking it might be a plugged cat? My exhaust seems to backfire frequently as well.

td1238

Backfiring (through the throttle), or detonation (through the exhaust) is often caused by sticking valves, which are rare on modern cars, but possible. I don't think that any sort of engine cleaning maintenance, or maintenance period, was performed on our '90 Civic until I got ahold of it, and it doesn't have sticking valves at 264,000 miles.

You can clean the engine out with some cans of B12 Chemtool. Marvel Mystery Oil is also good at loosening deposits and lubricating the valves. An overnight soak can be helpful. Putting it in your gas will clean the engine slowly. Several cans of B12 Chemtool in a quarter tank of gas will clean the valves slowly with a good high concentration of the cleaner.

Improper spark plug wire connections can cause back-firing and loss of power.


Could also be a timing belt issue, among other things. A jumped tooth will cause improper valve timing. At very least re-tension the belt to make sure that it doesn't jump, if it's been on there for a while.

Lack of power can be caused by a plugged catalytic converter. Haven't had one myself. Many say that you should not see more than 1 psi at the O2 sensor with a pressure/compression gauge on the O2 sensor port. Rev the engine a few times to observe. Don't let the hose melt.

I noticed a great improvement in power when I replaced the TPS. It had some faults at the low end that I didn't catch at first. Replacing and properly adjusting made for some rather impressive smooth acceleration, and low-end torque.

My original fuel filter was clogged solid at 200k miles. Replacement improved mileage greatly. I typically see low 30s in the city, and as high as 42 with a mix of city and country. I have a 1.5L. The clogged filter never caused any running issues, but it did make for a lack of power at higher speeds.

Power that comes and goes sounds more like something is intermittent, but all of the above items will improve power.

An improperly opening EGR valve will cause sporadic power loss. My '99 Saturn SL2 has one with an electronic monitor. When faulty, acceleration is poor because it opens too much. My '90 Civic does not have an EGR valve, though so no possibility of such a problem there.

Also, the exhaust is well tuned on these cars. Whenever I have a loud exhaust, I notice a lack of power. As soon as the exhaust is repaired, power picks up. The backfiring is another issue, though.

dstroman

how many miles? was the timing done at 100k and 200k? i would lean more towards td's idea of timing... not sure how it would be intermittent. take the valve cover off and at least check the belt out. u might even be able to see if its tight still. But it also really sounds like it could just be ignition. did you change your wires, distributor cap, rotor? it almost sounds like the wires were to blame and maybe when u put it back together they were fine until they moved or something. bad wires can arc right onto the engine. it wouldn't be a backfire though really more of a massive sputter. check ignition timing with a light too, its important

sellis1552

The timing belt appears to be in great condition. I'm not sure how long since it's been replaced though. I guess I could get that checked out, is there an easy way to test this?

dstroman

well the tension is important. im not as familiar with the D series engines as i am the B series integra engine but those have a spring tensioner and if it wears out a brand new belt will still jump cogs or worse with a bad tensioner. but how about plug wires distributor cap and rotor? if your wires are really bad they might be arcing onto the block. if its really backfiring though it probably is timing, either exhaust intake timing or the ignition timing. the egr could be involved somehow but i don't think egr problems are very common on hondas.

sellis1552

I'm almost positive a 94 civic doesn't even have an EGR. I can check the tension later on, I doubt that's the issue though. Plugs, distributor, and wires are all new. I do have a small oil leak behind the dizzy though, not that I think that makes a difference. I'm leaning more towards exhaust though, I have a few leaks and my cat could be clogged.

dstroman

this is a generic pic of what it might look like. all newer cars are required to use a EGR valve to improve emissions although i read that it is possible that 94 and older only required an EGR for California emissions. My civic is the same year and i haven't really looked to see but i know my 93 integra had a EGR valve. Try the pressure gauge on the O2 port before taking the exhaust apart. i don't think that would explain backfiring though. last car i saw with a clogged cat just had no power but wasn't really backfiring or anything. more of a constant sputtering.

sellis1552

I guess where ever I read online that 94 ex doesn't have an EGR was wrong. I'll try cleaning that. Anyone have tips on how to? I read seafoam might help.

dstroman

well im not saying it has one for sure but its possible. and if the emissions sticker is for california (assuming it hasnt been peeled off) then it almost certainly would have one.

as far as the seafoam you can unplug a vacuum line (like the brake booster) and while the engine is running you let the vacuum slowly slurp up the seafoam (do it in a small container so you can see whats going on, and dont let it suck up too much at once, for one thing if you do the engine will try to stall) but that could be something to try for a few bucks. and as far as the cat is concerned you could find a parts store that rents a gauge (usually u get all the money you put down on the tool back), although a friend of mine picked up a compression tester for about $20 from Oreilly auto

sellis1552

According to Honda-Acura.net the d16z6 engine doesn't have an EGR. So now we're back to step one. I could always try the seafoam to clean out my vacuum, but something is still causing me to lose power and fuel economy.

dstroman

like i said that could just be for california emissions. seafoam and try to get a hold of a compression tester or something u can plug into o2 sensor to check pressure before the cat, i got a o2 socket for about $5 from oreilly's. or just try taking the o2 sensor out (its a easier way) then just drive it and see if it seems better obviously it makes it really loud but i did this to check my cat on my saturn. when you say the exhaust is loud where is the noise coming from? is it louder in the engine bay, louder out the tailpipe, or louder somewhere in the middle of the car. a really crappy exhaust manifold gasket could cause some backfiring. if at all possible try to get some video on youtube of the problems you are having. might make diagnosis easier

sellis1552

When you say remove the o2 sensor, do you mean the one by the manifold or cat? And what should I expect as a result when removed? Will it run smoother without the sensor if my cat is plugged? And I know I have an exhaust leak near the tip, but i'm not sure why it went from loud, to quieter after tune up, to louder again.

td1238

My '90 Civic DX DPFI does not have an EGR valve, so it is possible that yours doesn't, either.

Retensioning the timing belt is done by removing the small black rubber plug on the side of the white plastic timing belt cover. Inside is a bolt that locks the tensioner in place. Loosen the bolt and allow the tensioner spring to properly tension the belt. Then retighten the bolt. Not sure of torque specs, but be sure not to over-torque it, but still torque it properly.

I have heard of people using compression gauges to measure exhaust pressure. You'll need a larger coupling to fit the O2 sensor hole.

Riick

Have you checked for codes? Spark quality? I know you're leaning towards an exhaust clog, but since these are simple tests seems like they just might give some insight into the problem. Post if you need to know how to check these things.

sellis1552

I have new NGK Iridium plugs, so my spark is fine. I'm getting it tested for codes tomorrow. My exhaust is not plugged, but the leak is progressively getting worse. I'm assuming this is the issue, since I can smell the fumes (burning rich) and losing power. I will be fixing it soon.

Riick

Easy to check codes yourself if you want...
Tools needed: short length wire, or paper clip.
Procedure: Find the small green rubbery box thing taped to one of the electrical cables way up behind the glove box. Rip it off the tape so you can get at it better, then pull the 2-wire plug out of it. Jump the connections by sticking the ends of your wire or paperclip into them. Turn the key to ON. Count the number of times the check engine light blinks, and that's your code. (Or, if it stays on steady, you have no codes.)

sellis1552

My check engine light does not work. I'm not sure what the previous owner did to f*** it up but they did something. That's why i'm just going to my friends garage. Thanks though, I didn't know that was possible.