I had my car out for a drive one day, was running reasonably well but its had a bit of a tranny issue for a while, same old junk. Had it out for a couple hours on and off. Finally am on my way home and get within 2 minutes of my house and i hear this massive backfire from the engine, then it does it again, then the engine starts stumbling, to the point where it does this the rest of the way home and i just barely get the car to my driveway. The engine will sit and idle fine but if you rev it up it just stumbles and backfires. I'm fairly certain its something to do with the ignition because it just seems like the timing suddenly went nuts. ALSO both my tach and my oil pressure gauge just died. What could all of these problems point to?

 

It's not the "timing". Put that out of your mind.

Sounds like either a very low battery, or resistance in the ignition circuit (or the battery feed to the ign sw) somewhere.

 

If the battery was that low my car wouldnt start. My car always takes a second to start anyways and needs a good charge to turn that big motor over.

How can you say it wont be my timing? Because the engine is getting fuel and spark, just not at the right time because its backfiring nicely. What im starting to think is could my ECM be fried? Because would that not explain 2 of my gauges dieing on me while everything else electrical in the car works fine. Also if it was basically dead it might idle but when i give it gas it doesnt keep up so the timing would effectively wander all over the place? I'm open to any sugestions, its not going to a mechanic because it isnt running well enough to get it there and i refuse to pay for a flat bed and a mechanic's diagnosis.

 

Allright well i just looked at a wiring diagram and hell if i can actually understand it but it doesnt appear that the gauges run through the ecm (please correct me if im wrong).

So this means i have an electrical problem. How would having a low batter effect anything because you can completly remove the battery once the car is started. So would that mean possibly its my alternator? how can i test to see if the alternator is still okay if that the case? please help me!!!!

 

The ECM doesn't run the gauges. They are not connected in any way, except for the 12V feed. The ECM can't make the gauges stop working. In fact, you could take the ECM out completely, and the gauges will be unaffected.

"Timing" won't make your gauges go away either.

Forget the "timing". It's not the cause of the problem. A symptom, possibly (but probably not); but certainly not the cause. Not likely to be a problem with the ECM either.

What kind of "big motor" is this? I though it was a 350? That's just a stock small block, and a little one at that. Is there more to this than we know yet?

In any case, don't be trying to invent weird one-of-a-kind theories involving complex mysterious phenomena, or any other kind of voodoo. It's just a car. Be logical and take things one step at a time, and you cannot fail to go directly to the problem. Confuse yourself, and .... you'll be confused, and you'll never get it figured out.

Always remember RB's First Law of Troubleshooting, which I borrowed from a much wiser man than myself:

"The simplest explanation that fits all the facts is usually the right one".

— Occam, ancient Greek philosopher, from back when all fuel injection systems were still mechanical

 

i am well aware of that im just using my limited knowledge to figure out what it could be. Allright so its not my ECM fair enough. By big motor its not its just that compared to civics, my engine takes a second or two longer to start up, and people always ask me why it takes a couple cranks before it starts running and i just tell them its because its a "big motor" it takes a second or two to start.

So if it is electrical it cant be the battery (as always correct me if im wrong) because that just runs to the starter, and is only charged by the alternator. However if things arent getting the current they require the alternator powers much of the engine and when i started the engine up last night i could hear a noticeable whine but couldnt trace it, could it be coming from the alternator as it's going out? How do i check to see if the alternator is okay? Any other insight as to what it could be?

 

You can check the alt when the engine is running, by measuring the voltage at the battery. The batt should have about 14V with the engine running, about 12.5V with the engine off, and should go no lower than 10V while starting the car. Typically with the engine running, the voltage from the big alt terminal to its case, will be a tenth or 2 higher than across the batt, since the alt is generating power at that time.

There are many connection points between the batt and the ignition system and the ECM. There's a fusible link at the starter that hooks the feed to the ign sw to the batt cable; there's the "bulkhead" connector, under the brake booster; there's a splice (maybe more than one) in the interior harness; then the ign sw itself; then to a splice where it gets distributed to all the things including the ECM and the gauges and the ignition system itself that need to be powered from switched ignition; and back out through the bulkhead toward the coil. High resistance, due to corrosion or whatever, at any of those points, could cause weird things to happen to the ignition and the ECM and the gauges.

Check the batt vlotage first, under all 3 conditions; and tell us what that is. Then we can go from there.

 

Update
Battery is at 12.25 when off and 12.75 when running, didnt have a second set of hands to test while cranking.

Oil gauge- Usually when the motor is cranking the gauge goes past the redline like all the way to the right, then once the motor is running it settles in the middle of the gauge. Now it goes all the way to the right when its cranking, and it sits where it should be when its off while the car is running.

Tachometer - When i turn the key so all of the battery stuff is on the tach needle bumps up from being off to just below where it starts to measure. Then as soon as i go to crank the engine the tach goes back down to when the car was completly off.

Also i think i forgot to mention that when the car starts up it runs like it always has, a little rough but fine. You have to drive it to the end of the street before it will start backfiring and stumbling, but then once you get it back into the garage it wont rev up in neutral.

 

Sounds like a new alt would be in order.

 

And why is that? While the car will run with no battery, it will also run with no alternator and it just needs enough charge off the battery. So if my battery is still putting out a 12 volt charge wouldnt it not matter if my alt is okay? I'm not trying to argue with you just spend too much time replacing the wrong parts. I will go to the local auto store and have them test it and see what the verdict is then go from there

 

Trust him, he's right. I have had that happen, well, quite a few times. My old system used to lunch an alternator like once every 2-3 months. The dummy light quit working for the battery, so when it was about to give, the car would start running like crap, backfiring and stuff. But when you shut it off, it would start right back up. Finalyl fixed that with a 140amp alternator. no more problems.

 

awesome, ya i was just going to post something saying that now that i think about it that explanation makes a lot of sense. Even if its not i need to check it off the list as possibilities so ill go and have it checked out tmw and maybe ill just get lucky. :lala:

 

okay got the alt tested and its fine.

What i find really odd about my problem, is both the tach and the oil pressure gauge both move when i go to start the car (the tach while the key is turned so the battery is on, and the oil pressure gauge goes all the way to the right when cranking) but then suddenly both go dead as soon as the cars running.

EDIT: The other option that im thinking of is maybe my oil pressure gauge is fine and its just not holding oil pressure because the motor isnt running properly?????

 

Well then, if the alt itself works right, but yet the voltage at the batt is low, then you have some manner of wiring or other issue with your car. I can't begin to guess what all that might be.

You might want to put a batt charger on it overnight and get the batt to a full state of charge, and see if the car behaves a little better. Then tackle finding out why the alt isn't charging like it's supposed to.

 

Why not take your alternator off and have it tested? Almost all parts stores will do it, for free, and it takes about 2 minutes.

If your alt is good, then thats one more thing to check off the list. But if its bad, then you know for sure what the problem is (or at least part of the problem).

 

RB83L69 my battery is wired up a bit oddly, got a kit to move the battery to the trunk, and it didnt include the wire for the alternator so i had to come up with my own wiring solution (this was about a year ago, it not the proper wire and i could do a much better job now i think the wire i used was a bit small). Since its not fantastically done it doesnt surprise me that my battery might be charging a touch low, however this shouldnt really matter because the wire that runs off the alternator to the battery is differtent from the wire that runs to the main power source on the car. So the alternator should still be enough to power the car. Ill take the battery out of one of the other cars in my house and see if my car works for a while longer but i doubt it im still looking for another solution.

 

Put in a new battery and it started up fine, idled roughly for about 4 seconds then died. Did that twice. Its not a battery issue.

 

Have you tried replacing the coil with a known good coil? That has happened to me once in the past too. I changed everything related to a tune up and it was still running **** poor. changed the coil, night and day difference.

 

replaced the coil (which was returned) and a distributor module already