Mechanics

WHY DID THE ENGINE GAG ON ACCELERATION, THEN BACKFIRED A BUNCH & NOW WON'T START?

1992 Subaru Loyale • 309 miles


I have a 1992 Subaru Loyale with 308K (80K on a rebuilt engine) and a few days ago I power washed the engine and cleaned the K&N air filter and drove it home with no problems. At home I changed the fuel filter and just before I started it up I wiggled the distributor cap and spark plug wires to make sure they were secure. Then the car started up as normal.

But as I pulled on the throttle cable the engine started to gasp. If I reved the engine up slowly the RPM will go way up and it sounded normal. But there is no power from the engine to actually drive the car. The car idled well for a while and then started less often. Then it wouldn't start at all and was backfiring too.

There was no check engine light on when the car was barely running. Sometimes in the past I had an intermittment idle problem where the check engine light would come on and the car would rev up and lose power and rev up again. If I just started driving or turned the car off and restarted this problem would go away.

So far to get the car running again I've changed the cap and rotor, plugs and wires, put in a new battery, checked all the fuses, made sure the spark plugs are getting a spark and checked the timing belts to make sure they are still in position.

I even put the old fuel filter back on since write after I replaced it was when all the problems started.

I replaced the fuel pump back in 2008 only to find out it was a bad pump relay wich I replaced with one I got from the junk yard. I still need to do a compression test. When I turned the engine over it doesn't sound so smooth and every four cycles or so hits a rough spot where the starter sounds strained. Still sounds of backfiring but not ignition backfiring.

Any idea what might be wrong? A mechanic is saying it might be the mass air flow sensor but I don't know how to test that other than to examine it and make sure it's clean, which it is.

Thoughts?
Avatar
Deanerimerman
December 29, 2011.



Backfire thru intake or exhaust pipe?

Tiny
Fixitmr
Dec 29, 2011.
Is the puter located where it coulda got damp. Try unplugging maf and see what changes?

Tiny
Fixitmr
Dec 29, 2011.
It sorta sounds like a timing or lean mixture problem.

Tiny
Fixitmr
Dec 29, 2011.
Thanks so much everyone! Here's a reply to each of you.

1) Backfire thru intake,

2) I'll get under the dash and check computer for signs of water and unplug and replug,

3) When I got the car 10 years ago the check engine light came on and it ended up being a dirty mass airflow sensor, so I've always made sure it's clean since then.

Do you think this is the intermittent idle problem that I mentioned in my 3rd paragraph above?

The timing belts were done 19K ago.

I had just finished up spending the day detailing the car when it died on me. : -) At least, I'm using the troubleshooting process to do more cleaning and maintenance, etc.

When the new engine was put in 80k ago the intake system was not rebuilt so other than cleaning out the intake manifold and crankcase hoses everything else has 308K on it.

Whatever goes bad on fuel and intake on these cars that I can do affordable maintenance on right now is definitely what the highest priority is once I get the car running again.

Most of all, I really, really want to get this car on the road so I can safely make my 800 mile drive home from holidays with the family.

So a priority for me is the intake system hasn't had any kind has been but I've never dared take apart the single-port fuel injection system to do maintenance. What kind of maintenance do they require?

Or could it possibly be the fuel pressure regulator? 'Cuz I had a hunch about that?

Tiny
Deanerimerman
Dec 29, 2011.
Backfire thru intake is too lean or bad timing like spark wires crossed?

Tiny
Fixitmr
Dec 29, 2011.
Fuel pressure test is in order also. Usually fuel regs go bad by leaking thru and making car run rich.

Tiny
Fixitmr
Dec 29, 2011.
Has TPS ever been changed?

Tiny
Fixitmr
Dec 29, 2011.
The TPS has never been changed. I looked online and that's a $200-$300 dollar part unless I find one at a junk yard. Is there any way to test it? I guess I could take it out and clean it and inspect it first?

I double checked spark plug firing configuration. Looks good. Ignition Timing was okay before it broke.

I have an after market super coil which I put on 8 years ago thinking I'd get better gas mileage. Would an extra hot spark create damage of any kind over time?

Note: two of the spark plugs I replaced look normal and two of them more dry carbon than usual.

My plan is to spend the next few days taking stuff apart and cleaning, inspecting and testing and if I can't get it started by Monday I'll get it towed to a local mechanic here east of Sacramento.

Could this be related to a vacume leak or something related to the vacume canister? Last year I replaced the vacume switch that takes the car in and out of 4WD. And many have suggested that a vacume leak would cause that idle problem I've been having. But all the hoses look great?

Basically if you can tell me anything and everything that I can clean and inspect and test with a multi-meter that'd be great!

I really appreciate your help. I'll for sure make another donation if this conversation continues a couple few more times.

Tiny
Deanerimerman
Dec 30, 2011.
Definately a vacuum leak would cause the symptoms. WOW, that's an expensive TPS! I uses a pocket(MM) ohm meter to check it's smooth 'no blink' operation.

Tiny
Fixitmr
Dec 30, 2011.
And no, high out put coil should not be a problem unless it is failing itself.

Tiny
Fixitmr
Dec 30, 2011.
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