Miss during hard acceleration

[davekp]

Experiencing a miss- actually like a cough, under hard acceleration. Occurs once, like a momentary ignition failure, then comes back on as normal. '91 302 with throttle body efi. Most noticed in second gear.
Maybe a coil breaking down?
Other ideas?
Thanks in advance.

[brewha]

Maybe a plug wire jump...or an arc in the cap...or a coil issue

[Itchief]

Have you tried increasing the pump squirt value on the EFI?

Rick

[davekp]

Have you tried increasing the pump squirt value on the EFI?

Rick

No-don't know what that is. Please explain.
I have just changed to 24lb injectors with matching MAF and 70mm throttle body.
Also, am getting a mild backfire between shifts.

[FLPBFoot]

Sounds like you are running rich? What do the plugs look like? Black?

[davekp]

Sounds like you are running rich? What do the plugs look like? Black?

Haven't checked the plugs but the exhaust pipes are sooty. Running rich is very likely.

[Jeff Kleiner]

Sooty pipes notwithstanding---a stumble/miss under load and exhaust backfire can both indicate a lean condition. If you assure that the plugs are OK try unplugging the oxygen sensors as an experiment. If they got gacked while it was trying to run when you had the incompatible injector/MAF combination they may be giving the ECU bad info which it is trying to compensate for. With them unplugged the O2s will not be not talking to it the ECU so it won't go into closed loop and will just run it off of default tables. If it gets better then check the sensors.

Jeff

[davekp]

Here's some not so good pics of plug #4- looks lean to me.

[Jeff Kleiner]

Here's some not so good pics of plug #4- looks lean to me.

As I said above, some of your symptoms sound like a lean condition.

Jeff

[davekp]

Any way to clean or refurbish the O2 sensors if they are suspect?

[Norm B]

You can remove and try to clean them with throttle body cleaner. Blast them dry with compressed air. Do not scrub them with anything. The ECU should throw a code if the O2 sensors are bad for an extended period.

HTH

Norm

[Itchief]

No-don't know what that is. Please explain.
I have just changed to 24lb injectors with matching MAF and 70mm throttle body.
Also, am getting a mild backfire between shifts.

Dave


Accelerator/pump, pump Squirt is used To assist in throttle transitions the Atomic EFI has a feature to mimic the pump squirt of a carburetor. This works by increasing fuel delivery by a prescribed percentage any time there is an increase in throttle position. If needed, make small changes of no more than 5% increments without further testing. 25% is sufficient for most engines. Almost all vehicles will use between 15 and 35% pump squirt

On my tb EFI the engine would stumble as you depress the accelerator as Jeff indicated a lean afr once you got to wot the miss would stop. I increased the pump squirt value on my setup the stumble/miss stopped

Your EFI setup may refer to it as some other name

Good luck

Rick

[Railroad]

Move the lean cyl inj to another cyl. See is the lean condition follows, or just replace the one injector.
Unless the TB houses the injs.
good luck,

[davekp]

Dave


Accelerator/pump, pump Squirt is used To assist in throttle transitions the Atomic EFI has a feature to mimic the pump squirt of a carburetor. This works by increasing fuel delivery by a prescribed percentage any time there is an increase in throttle position. If needed, make small changes of no more than 5% increments without further testing. 25% is sufficient for most engines. Almost all vehicles will use between 15 and 35% pump squirt

On my tb EFI the engine would stumble as you depress the accelerator as Jeff indicated a lean afr once you got to wot the miss would stop. I increased the pump squirt value on my setup the stumble/miss stopped

Your EFI setup may refer to it as some other name

Good luck

Rick

I don't think this applies since I have the OEM EEC IV system.

[davekp]

Move the lean cyl inj to another cyl. See is the lean condition follows, or just replace the one injector.
Unless the TB houses the injs.
good luck,

Good idea. Could one or two bad injectors cause my problem?

[Jeff Kleiner]

What do the other 7 plugs look like Dave?

Jeff

[Walt]

Could be a bad or dusty MAF. I had it happen on my 93 mustang, would be ok then would miss under power.

[Richard Oben]

Turn the fuel pressure up a bit if you have an adjustable one and see if that helps. R

[davekp]

What do the other 7 plugs look like Dave?

Jeff

All are the same except #1. Looks like it wasn't firing. Will check temp at that header pipe next time I start it up. If not firing will check spark. Maybe a bad injector? Can't drive it for a few days since I'm in the middle of doing a mechanical throttle linkage mod. And a lot of other "projects"!

[Jeff Kleiner]

If they all look the same that rules out the possibility of "one or two bad injectors".

Jeff

[davekp]

If they all look the same that rules out the possibility of "one or two bad injectors".

Jeff

But the #1 plug was different, so I'm not ruling anything out yet. Could one bad injector cause the miss?
Also removed and cleaned the O2 sensors. They were very sooty.
Thanks!

[CraigS]

Yes it could. Also, if a cylinder isn't firing, it isn't burning the gas OR the oxygen. So the O2 sensor on that side of the engine sees more oxygen, and starts adjusting the mixture.

[Jeff Kleiner]

Sorry Dave, I misunderstood what you said and thought you indicated that they all looked the same like #1, not that #1 was different. In that case, yes it could well be an injector---HOWEVER---when we first built the car it had an intermittent on (as best I recall) #7 or 8. After putting a noid light on it I found that the pulse to the injector would come and go and traced it back to bad contact on that injector's wire at the salt & pepper plug. I think Aaron eventually eliminated the S&P plugs and soldered all of the wires but can't say for sure. If you have, or have access to a noid light (I think most Autozone and Advance Auto stores have them in their loaner program) I'd first check it out electrically and if that shows good you could then swap injectors and see if the problem follows. As Craig already pointed out if one cylinder is not running the oxygen sensor will report lean to the ECU and it will richen the mixture ON THAT BANK to try to bring it in which could account for the pipe and sensor looking sooty. Again though, that would only be on the one bank.

Let us know how it goes.

Jeff

[davekp]

The S&P plugs are gone.
What's a noid light?
Although both sides were sooty, only the #1 plug looked different.
Wil continue the troubleshooting.

[davekp]

Update:
The good news-
Cleaned the O2 sensors, installed the correct MAF and new injectors. Great acceleration, some slight sooting in the exhaust. No breakup.
The bad news-
Got a speeding ticket while checking it out.

[Just puttering]

Post 4 listed new inj. MAF and TB! Then you installed the correct MAF and inj. To fix it in post 25.
What changed from post 4 to 25 on your setup?

[AC Bill]

Post 4 listed new inj. MAF and TB! Then you installed the correct MAF and inj. To fix it in post 25.
What changed from post 4 to 25 on your setup?

I agree that was confusing..:confused:

[davekp]

Post 4 listed new inj. MAF and TB! Then you installed the correct MAF and inj. To fix it in post 25.
What changed from post 4 to 25 on your setup?

I incorrectly had a MAF for a '94, but I needed one for a '91. They are different. I also cleaned the O2 sensors. Since post #25 I discovered I had the wrong spark plugs. Changed these to the correct plugs.

[Norm B]

All of your previous problems are most likely due to the 94 MAF. From the research I have done the outputs are completely different from the 93 and earlier MAF. Your computer would have been trying to compensate for some pretty weird airflow readings.

[davekp]

Yes, That seems to be the case.
When I put in the correct MAF but still had the incorrect plugs, I was getting a rich (I think) condition on #1 cylinder only. I'm waiting for a few trips to examine #1 and see If I still have something going on there.
BTW, I really get nervous when removing and installing plugs in aluminum heads, so I'm giving it some time.

[Ian G]

Hi. This won't help your original problem but Always!! use anti-seize compound on spark plugs going into aluminum heads.

[davekp]

I always do.
But I still get nervous.

[Just puttering]

Sorry to take you down a side route.... The last time i put in plugs, no anti-seize. So, i got worried and started searching.

The one thing i will mention here is with lube on the threads, i read that you should decrease the tourqe on the plugs! It looks like the big issue is over tourqing the plugs and deforming or pulling the threads!

Here are two references
https://www.motor.com/magazine-summary/trouble-shooter-mar-2013/

https://agradetools.com/be-confident-with-anti-seize-how-to-use-the-right-anti-seize-like-a-boss/

[davekp]

Problem seems to be solved. I think I may have had an issue with the #1 plug terminal not fully seating on the plug resulting in intermittent firing.

[NAZ]

I'm absolutely anal about using a torque wrench on fasteners but spark plugs are not an item I typically torque. But yes, if you use a lubricant on spark plugs it significantly reduces the torque required to tighten them (just like fasteners). On aluminum heads you should consider using anti-seize containing zinc and use plugs that are zinc or cad plated. Plugs with that black oxide coating may react with the aluminum if left in place for extended periods causing the aluminum to act like an anode and damage the threads in the head.