1994 5.7 TBI running rough, backfiring

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yep, disconnected the exhaust today and same thing....also, the cat has been gutted at one time or another...I can see all the way to the O2 sensor sensors and neither pipe appears clogged....tested via a coat hanger.

I would think it almost has to be the ECU....it doesn't seem to act the same way twice.
 
FWIW, a quick google found guys typically run 6 degrees initial advance. Apparently my Ford number of 10 degrees is too much, LOL
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The balancer has slipped on the rubber causing the timing marks to be off.
 
Originally Posted By: jegs
The balancer has slipped on the rubber causing the timing marks to be off.


Good call!!! I forgot about that being a possibility!
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Used to happen to the OE Mustang balancers too.
 
Originally Posted By: Nick R
Just going to throw this out there, but did the timing chain maybe slip a few teeth? Wouldn't that cause this sort of behavior?


SBC/SBF chains don't normally "slip teeth", as they are very short. And while it would retard or advance the camshaft timing, it wouldn't affect his ability to set the ignition timing.
 
It's not uncommon for folks to replace their ECU on these trucks. They aren't that expensive either....actually, nothing is expensive on these trucks....unless you go replacing parts trying to fix it, without diagnosing it. But that happens. I totally understand.

I might be wrong, but I think advancing the time means the timing mark should slide towards the passenger side. That is "advancing." I'm pretty sure. Wouldn't bet my life on it....been awhile since I've had to re-time mine.

Doesn't your reference plate have numbers on them showing which way is which?
 
Originally Posted By: Phishin
It's not uncommon for folks to replace their ECU on these trucks. They aren't that expensive either....actually, nothing is expensive on these trucks....unless you go replacing parts trying to fix it, without diagnosing it. But that happens. I totally understand.

I might be wrong, but I think advancing the time means the timing mark should slide towards the passenger side. That is "advancing." I'm pretty sure. Wouldn't bet my life on it....been awhile since I've had to re-time mine.

Doesn't your reference plate have numbers on them showing which way is which?


I believe it is illustrated in the video I posted.
 
Originally Posted By: OVERKILL

I believe it is illustrated in the video I posted.


Yeah, I think the big "V" all the way on the driver's side is the 0 timing mark. So, advancing the timing goes towards the passenger side.

If your timing mark is at zero, and then moves further to the driver's side once the tan est wire is plugged back in, your ECU is toast.
 
thanks folks for all the input....I'm going to try an ECU. It isn't that expensive and the fact that this truck doesn't act the same way twice leads me think it may be the ECU.

Yep, I agree about not throwing parts at it. It must be fairly simple (like an ECU) as my grandson told me the truck was fine when he left work the night before; the next day heading to school he said it started running worse and worse and then started backfiring. I wasn't aware of how bad it was until he brought the truck to me (I still can't believe he drove the truck 75 miles to my place) It's no wonder the cylinders were fuel washed and I'm sure the backfiring (it's BAD) probably caused some of the damage.

His uncle replaced the MAF and other parts trying to fix it....so they were trying but this was/is a tough one. I have to get the number off of the original ECU and then order it. Hopefully, this is the charm....the truck runs great when running but then gets a wild hair and all bets are off.

I'lll let you know folks......
 
MAF? I wasn't aware that the TBI trucks had mass air flow sensor.

I agree with Phishin on the timing thing... Odd considering. On these trucks timing is to be set at zero with the brown/black wire disco'ed. ECM handles advance from there on out. Once set, you'll typically see 15+ degrees at idle.

Before tossing an ECM at it, check the EST module (typically mounted to the intake) and the control module (under the distributor cap). Most parts stores can handle this.
 
I'm sure he meant MAP, not MAF. Besides, all it does is open the egr. That wont cause these problems.

Not sure what you are referring to when you mention est module.....
 
Depending on price, I would consider local wrecking yards for the ECU. They are very easy to access and remove and the numbers are on the sticker to find a match.
 
Originally Posted By: Phishin
I'm sure he meant MAP, not MAF. Besides, all it does is open the egr. That wont cause these problems.

Not sure what you are referring to when you mention est module.....


Spark control/EST
 
Yes, MAP not MAF.

I agree with phishin that the ECU is bad....the timing never acts the same way twice. Last night I started it.....fired right up and idled smoothly....revved a few times and again, bogged down, backfiring and the timing mark, with the est wire connected is all over the place but is staying primarily near zero....it does move when you increase throttle but moves the wrong way, i.e. less advance to after dead center (which could also be the rubber slipped on the damper).

The ignition module has been replaced. Remember folks, this problem started all of a sudden and I think the engine damage was caused by continuing to drive it while acting up. I'm really surprised he was able to drive it at all.....I can't get it to pull my driveway without backfiring and bogging down....exactly like the timing is off....which it is.

The price of the ECU at AA is very reasonable so once I get the original number, will order it today.
 
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Originally Posted By: mechtech2
Advance your timing - please!


mechtech, are you advising to advance the timing contrary to the book spec?
 
Folks.....remember, this engine was running perfectly one day and the next start, problems were obvious. I think the way it is running is what caused the damage.

I have a PCM on the way and I picked up a distributer....just in case. I want this truck OUT of my garage. As stated in several posts earlier, the timing is all over the place and seems to want to settle around zero or after tdc. If I disconnect the est wire and time by ear, it sounds great but as soon as I plug in the wire it goes to hello. I checked the damper timing mark today (nylon cable tie through the plug hole) and verified tdc and mark lined up.

And yes, the distributer is installed correctly.
 
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