EFI Woes......$100 Reward for help offered

[danj]

I have an 83 280ZXT with a 383 stroker, Vortec Iron heads, 700R-4 and stock turbo rear.

 

I'm running an Edelbrock Pro-Flo EFI system that is malfunctioning and so far no one has figured out what's wrong with it. The symptom is that the engine backfires through the tailpipe continuously as if the plug wires were rearranged, which they are not. But that is what it is doing.

 

The engine and EFI were apparently doing fine until I took the car to a tranny shop and let the guy run a 1/2" gas line in lieu of the 3/8" gas line that comes with the EFI system. I'm running about 42 psi through the fuel rails, which is correct for the system specs, so it doesn't appear to be a fuel problem. I cleaned the injectors and rails just to be sure. I worked with the Edelbrock tech people by phone for a few months and they ran out of suggestions. I changed plugs, checked the plug wires, distributor, coil, battery voltage to the system, and checked all resistances for the wiring of the EFI. Changed out most sensors. Checked the cylinder compression. Ignition Amplifier. Changed out the gas. Reset the timing to the base setting for the system. Checked and reconnected the EFI ground wires, etc. Even sent the ECU back to Edelbrock for testing and they sent me another one that did the same thing. The handheld programming module isn't flashing an error message. I am using the Mallory Hall Effect distributor that is made for the system.

 

I am thinking that it is still some kind of a wire or electrical connection problem of some kind that I have somehow overlooked. Edelbrock says maybe the cam is out of phase, but the system was running OK and the cam hasn't been touched.

 

I am so frustrated with this that I am left with 2 alternatives. Do whatever it takes to get the system running or change it out for a 4 bbl carb set-up.

 

I don't know if it's proper or not in this forum but I would happily pay someone $100 if they can offer a solution that works.

 

Any knowledgeable input from experienced EFI guys would be greatly appreciated.

 

DanH

[dmyntti]

It could be mechanical. It is possible that the timing chain slipped a tooth. Another possible problem is a burned exhaust valve. This will cause a popping in the exhaust though I have never heard one be terribly loud. A compression check can rule out these problems. After that you are looking at either fuel or spark issues. Spark is easy to check with a timing light to make sure you are in the ballpark, or you could just advance the distributor (turn counterclockwise) to see if this helps. Once you are satisfied with these two you must look at fuel issues. You could concievably be popping in the exhaust with either a way rich or a way lean condition. If the car runs long enough you could check the color on the spark plugs white would indicate a lean condition black a rich condition.

 

Just look at it one system at a time.

 

Hope this helps.

[MONGO510]

I would check to see if the fuel pressure regulator is damaged or has been tampered with. It may have a leaking diaphram.

[danj]

I appreciate the input. I'll accumulate any replies I receive during the week and work on the car on the weekends to see if any of the proposed solutions can solve the problem. I did run a compression check which would generally eliminate a valve problem. I have set the base timing as required for the EFI system to enable it to adjust spark properly. I can get the engine to smooth out some by retarding the timing through the handheld module by the max allowable of 16 deg. I'm not sure if this is telling me I have a timing chain or cam phase problem, or if the system is just self-adjusting the timing for a fuel or other electrical problem. The system always strives to reach a balance betweem rich/lean whatever it takes, so it's hard to know what the problem is that's causing the system's timing adjustment to be so far out of whack.

 

The fuel pressure regulator I'm running isn't the stock one that came with the system. I'll check that out for a possible leak.

 

DanH

[dmyntti]

I think you would know if your timing chain had slipped from the compression check (the compression would be low). I also think you hit on the problem when you retarded the timing at the controller the way you did. You might try adjusting the distributor to see if it helps. You could have a problem with the distributor itself (i.e. the ignition module/coil/pickup etc.).

[danj]

Don

 

I'm not sure what you mean by "adjust the distributor". I turned the distr. as necessary to get the base timing as required by the Pro Flo system. The local speed shops don't have a tester for this distributor. It is a Mallory system that's made especially for the Pro Flo system with the "Hall Effect" set up. I did have the Blaster coil tested and it was fine. The ignition system has an Ignition Amplifier that also checked out OK. How would I go about checking the distributor further? Also, the compression check was normal and even across all cylinders.

 

DanH

[Bartman]

Not sure if this will help, but what size return line are you running? Maybe the return line is too small to return all the unused fuel back to the tank.

 

You stated that this problem started when you let someone switch your supply line to 1/2", so it makes me wonder if having a 1/2" supply line is the problem. Here's an article I found that may be of interest:

http://www.carcraft.com/howto/56398/index2.html

[mobythevan]

When I first installed megasquirt on the 350 engine with TPI we had a problem like this and it was caused by the spark jumping posts in distributor when timing would get advanced revving the engine. it would run pretty good and then advance would reach a certain point and pop, pop, pop. This was fixed by phasing the ditributor. Could it be that something has slipped on the dizzy drive shaft or in the top part at the rotor causing a rotor phgasing problem like the one we had?

[BrandonsZ]

If you have a Cat or not there is only one way to get popping in the exhaust OXYGEN AND FUEL.

 

If you have a rich condition, all the useable OXYGEN is GONE. So the next question is HOW did OXYGEN AND FUEL get into the exhaust? Well, a rich condition coupled with an exhaust leak could cause air to enter the exhaust if you have a VERY free flowing exhaust it could actually scavenge air into the exhaust and cause the unburnt fuel to ignite (usually when hitting something hot like a cat).

 

If you have a lean condition, all the useable FUEL is GONE and you couldn't have anything to pop.

 

You must either be exhausting unburnt air/fuel mixture into the exhaust in which case you would be hearing or feeling a "miss". This would not necessarily cause your problem because even a car that misses badly doesn't backfire constantly.

 

 

IF you truely are hearing what you think you are hearing, the exhaust would be getting red "cherry" hot the situation and must be a firing of unburnt Fuel AND oxygen in the exhaust which is a no-no because that is energy you could have used AND your cat, if you have one, will be trashed in no time.

 

So how does unburnt fuel AND oxygen get into the exhaust? through the exhaust valves, through a miss, if you don't have a stuck valve for static compression testing but you just happen to have a stuck valve during operation, this could be the fault of a longer than required pushrod acting on a hydraulic lifter (obviously not your case since it was fine before but humor me) At static conditions the valves have no life because the lifters are compressed, the engine needs to be running to get the lifters to work. SO have a dynamic compression test. The valve trane could still be responsible if your rocker was bent or your rod was just barely too long or the exhaust valve is sticking only when running (broken spring).

 

Check your valve trane get the dynamic compression tested and then when you've exhausted all those efforts, do this (which is what you should have done first).

 

 

1. Remove the ignition cap and all wires from the car, DO NOT MARK THEM.

2. Get a good book that tells you your firing order and put them back on checking them as you add them.

3. Replace the cap with a new one.

4. Inspect ALL wires everywhere and make sure nothing is rubbing/grounding.

 

If that doesn't solve it,

 

5. Remove that EFI and get an Avenger AVS.

 

Thank you, where's my $100?

[danj]

I appreciate the responses I've received so far on this EFI/Backfiring problem.

 

I'm going to begin tackling them one at a time this weekend, naturally beginning with the easiest and cheapest possibilities, and work from there to whatever it takes. The $100 reward is absolutely guaranteed and will be happily sent to the source that hits the nail on the head and gets me up and running again.

 

DanH

[VinhZXT]

A friend of had a back firing problem awhile back and it turned out to be a cracked distributor cap. Eventhough we couldn't see the crack very well but when we put another cap on and the problem went away. Hope that helps. GL

[80LS1T]

Now I havent seen this on any small blocks but I did see this on a Dodge 4.7L...

 

The engine was running like ok but not normal. It had a lost of power and felt like a slight misfire but nothing was showing up on the OBD2 misfire monitors with the scanner. What it turned out to be is the dowl that holds the cam sprocket on the drivers side had broken and the sprocket spun just a little causing the timing to be off.

 

If it's not too hard you could always put the 3/8" line back in and see if the problem goes away. Did you check your tune with a wideband after installing the new fuel line? Maybe it changed enough to cause it to run rich?

 

 

Guy

[kcelectronics]

Is there any chance that when the new fuel line was run metal splinters or dirt has jammed open one of your injectors? this is the reason that F/I cars run high quality filters and dirt/crap IS the main cause of miss firing on stock F/I engines (usually after home servicing)?

 

Pull the injectors reconnect them to the rail and pressurise the fuel system, then check for fuel leaking from any of them they should be bone dry.

 

 

Chuckie:twisted:

[george.bryant]

Oxygen Sensor(s) fouled and putting out a bad signal? Or incorrect EFI fuel filter? Leaking leads or coil?

[wheelman]

Really sounds to me like the distributor is out of phase. I just put a new timing belt on a Volvo that had been sitting for a year waiting for it and had also been worked on by someone else before I got it. When I put the belt on it pinged real bad, not back fire but ping. Turned out the prior "mechanic" had re-phased the distrbutor in an attempt to set the timing after the belt had slipped. Took me a couple days to figure this out but once I put the dist in correctly it ran great.

I guess the next question is how would the dist have gotten changed while it was at the tranny shop?

What all did they do?

Did they pull the engine/tranny to run the fuel line?

 

Anyway, something to consider, along with looking for a cracked cap and also burned plug wires that are arcing between them causing spurious firing.

 

Wheelman

[80LS1T]

Yeah maybe the guy who ran the fuel line pulled the distributor out to get better access and damaged it or put it back in wrong?

 

Guy

[danj]

I am still working through the proposed solutions I received. One of the problems with the Edelbrock Pro Flo EFI is that it is easy to set up and tune since it doesn't require a laptop to tune, but it is difficult to troubleshoot since there isn't a diagnostic computer-based set-up that allows you to see what the ECU is seeing.

 

Anyhow I am going through a lot of analysis and testing, and should have an update by the end of this weekend.

 

Dan H

[Tony D]

You know, with all that has been mentioned, nobody has talked about crossfiring between #5 & #7 wires. Once it is initiated, the engien continues to run with it like that, jumping between wires laid in paralell for a distance.

 

When I was in tech school, a Champion Sparkplug rep showed us with the plug wires simply CROSSING each other at right angles!

 

Makes for annoying, consistent backfires.

 

And as Moby said (like I experienced when my initial timing on the disc was set too far advanced), the engine could jump phase on the terminals, and once it's there, it will keep firing that way till it jumps back!

 

Good Luck, M8!

[dr_hunt]

Well, in the old days, we used to turn the ignition off while driving down the road with a manual transmission vehicle. Pump the throttle a few times and then turn the key back on. Get one hell of a backfire out the exhaust.

 

That is usually caused by a buildup of unburnt fuel in the exhaust that becomes ignited by another flame propogation or just high temps in the exhaust.

 

In your case I would suspect a poor tune with the efi that results in a rich condition at some point in your map coupled with not enough timing. Not enough timing causes backfire on deceleration. Rich condition causes the same thing on acceleration when coupled with slow timing.

[danj]

Well, after 2+ years of trouble shooting and just sitting idle in the garage, I took the car to a hot rod mechanic I met recently at a classic car show here in Tulsa, to have him give it a final diagnostic before giving up on the EFI system and converting back to a 4 bbl set up.

 

I called Edelbrock EFI tech support 1 more time to see if there were any more tests we could do that haven't been done. They told me that a problem was recently discovered with the Mallory Distributor that had been custom made for their Pro-Flo system. Seems that when the unit heats up the shutter wheel below the plate in the distr. moves which puts the distr out of phase with the cam. The timing will look right on the crank, but will not fire correctly. Once this wheel moves the 1st time, it never returns to it's correct starting point to reset. Also, a physical exam doesn't reveal a loose shutter wheel.

 

Anyhow, to deal with this problem Edelbrock obtained a supply of the necessary fix-it parts from Mallory (Mr. Gasket) and they do the testing and repair in their EFI shop and return the distr units within a week. We shipped it off, they tested and found it defective, did the repair, and returned the unit. That stopped the back firing problem and I drove the car home from the shop today. 1st time the car has been driven in almost 3 years.

 

Now my problem seems to be what kind of rear end/wheel/tire set up do I need to contain this beast.

 

Thanks to all for the suggestions. It appears that the problem was pretty much unsolvable until Edelbrock discovered the Mallory Distr. defect.

 

DanJ