My car runs flawlessly when you first start it up for about 1-2 minutes. After this is starts randomly missfiring. It might stop for a second or two but then it starts back again. Some misses are really bad and makes the entire car shake like its multiple then some seem more like mild singles. Also, for the first 1-2 minutes on startup when its running fine my fuel pressure is stable around 40 give or take 1psi. When it starts missing its all over the map from 40 down to the low 20's and everywhere in between. Voltage to the pump does not correspond at all with misses as its alway between 13.84-13.96. I dont know if my missfire and fuel pressure are seperate issues but I believe they are the same but who knows. Any suggestions on things to check? Anything is appreciated. Going racing tonight...to watch...

94 Mustang GT: 351 swap with t70turbo
Parts list again:
a1000
aeroquip pushloc lines to aero y block feeding each rail
mototron 60lbs
aero fpr return style
msd digital 6
msd hvc blaster coil
msd super conductor plug wires
new autozone (cheap i know) distributor (replaced during troubleshooting with no change)
new autozone ignition module (replaced during trouble shooting with no change)
all digital guages
tuned via tweecerRT

Note: MSD has been bypassed completely and still has same problem

 

Have you checked the injectors? Check the resistance between the two terminals on each injector then between the terminals and the body of the injector, there are two small holes in the side of the plastic body, these holes allow you to check resistance to the steel body of the injector. The resistance between the two terminals should be close to the same on all of the injectors, if one is noticealy differrent, it could be bad. There should be no continuity to the body of the injector. Check the injectors after the engine has been run for a while. I had a Ranger awhile back that when cold the injectors all checked out good, but after running the engine for 15 minutes the truck would miss, I finaly pulled the upper intake after it had been running for a while and found one injector that had a short to the body. Also make sure you are getting good power to all of the injectors, and check the harness with a noid light. Could be a bad EEC power relay or splice coming from the relay with high resistance. My car had high resistance in some of the splices coming from the EEC power relay and so the wiring and relay would get very hot after running a few minutes. If the key was on and the engine was off the wiring would not get hot, but if the engine was running the wiring would get hot. Could also be the ECM or an ECM ground. Possibly there is a problem with your regulator, make sure the diaphram is not busted, pull the vacuum hose and see if you get any fuel out of it.

 

Injectors have crossed my mind once or twice, my knowledge of putting a together car is next to none but troubleshooting is def my weak point. I will check the injectors out first as well as the other things you mentioned and go from there.... Could the problems you name cause the fuel pressure to jump all over the map after a min or two or running? My pump has been suggested to possibly be the problem for this (bad seals/magnets???) and im trying to determine whether i need a rebuild or just get a new one or hopefully netiher. Any ideas about that problem?

Thanks,
Mark

 

Any suggestions or reasons for the fuel pressure fluctuations?

 

Have you checked the regulator, do you know for sure how much fuel is in the tank and how low is the pump mounted? If the pump is not as low as the lowest part of the tank and the fuel level is low it may not be picking up fuel properly. When I first read your question, some of the symtoms seemed simular to a problem I found a few months back, but later reading what you have for a fuel system and that you are running 60 lb. injectors, I don't think eight 60 lb injectors could cause a fuel pressure drop or fluctation if they were stuck wide open and then if there was a problem with the injectors I would not expect more than two to be bad at a time. Listen to the pump when before the car starts missing and while it is missing, if there is a change in the sound of the pump like it is speeding up and slowing down rappidly, it may be sucking air. If it sounds if it seems to get quieter than it was when the car was not missing and possibly fluctuating rpm it could be a bad pump.

 

Try replacing the coil.

When my coil started to fail, my car did the same thing.

 

I havent checked the aer0motive regulator. Dont really know of a way to test the regulator. Ill try to read about it. Dont have any friends who have a spare one to swap either. As far as the pump, its an externally mounted a1000 with a built-in internal sump (from Glenn's Performance). The pump is mounted on a fabbed up bracket below the tank facing towards the front of the car. It has a litte over a 1/4 of a tank but it was doing the same think when i was crusin around with 1/2 tank. I dont know for SURE how much is in the tank, i suppose the gauge could be wrong but when i topped it off or close to it (10 gallons) it was also doing the same thing.

As far as the sound of the pump it stays the exact same. I crawled up under it for a few minutes to hold the voltmeter on it and it was reading 13.8x volts the entire time with no sound or pitch change even though the rpm's do occasionally move slightly around 200rpms at most but thats only when it misses really bad and almost seems like its trying to go dead. I dont know if this helps but when it starts missing the gas smell becomes so strong it makes your eyes water. I wish my piece of crap innovative a/f gauge would work but if it was im sure it would peg to 10:1

 

I thought this myself initially as well as the MSD box possibly being to blame so i bypassed them both and used my friends stock coil that he runs without a miss and my car still missed with his coil and msd completly bypassed. I might try bypassing everything else again when I check out the regulator and injectors hopefully in the next week or to. Just trying to get a list of things together to check so i can tackle them all in one day. But i appreciate the help!

Mark

 

Ok.

I am not super familiar with the tweecer, but does it use a wideband or signal from an o2?

On some of the systems, they will start in open loop and then move to closed loop after a certain time period. If the o2 is no good, it may be trying to correct off the signal and dumping a ton of fuel in when it doesn't need it.

 

Interesting, the past few times i have started my car it has had a decent bit of moisture coming out right after startup which could have trashed my o2. I mean, its possible that this could be could be one of the problems but my car has had this miss for a while (its just recently gotten worse). I will make a log of my short fuel trims and see what kinda numbers im getting from my o2 and go from there. I guess I would also reset my KAM tables and see what that does. Ill check all the things that everyone has sugggested and see what I find.

Thanks,
Mark

 

Yeah I was thinking the same thing that most computers when cranking are kind of like in choke mode and run a little bit like that til they go to normal operating mode.Make sure there are no vaccum leaks.That could cause fuel to fluctuate and idling bad.

 

sounds like once you get into closed loop, it starts fucking up.

read this

http://www.modularfords.com/forums/showthread.php?t=58339

probably your o2 sensors, but most likely a sensor of some kind.

 

Bringing back my old post now that ive tinkered with it some today (not much). I did some data logging and such and am posting this on the tuning forums so they can take a glance at it but what i found today was that when I removed my vacuum hose from my 90 elbow going to my fpr for a pressure/vacuum reference and plugged with fpr side with my finger the pressure quit fluctuating and actually shot up to about 50ish and was pretty stable +/- 2psi. As soon as I slipped it back on the fpr reference nipple it started going crazy again, even as low at the upper teens. It never did this before, is my fpr bad? any suggestions?

Second thing that doesn't seem right is when i start the car there is always so much condensation coming out of the downpipe that the concrete is wet up under the car. I can move the car turn it off start it right back up again and presto ground wet again. Figured this could be ruining my wide and narrow sensors. Anybody else ever had this problem? I mean it is 50ish during the day and as low as 20's during the night so this could contribute but i wouldnt think it would be so much.

Thanks,
Mark

 

what filter are you running before the pump ? where is the pump located ? sump or straw ?

alose you sure you have to correct firing order ? 13726548 for the HO

 

Dont see why i wouldnt. Lined balancer up on zero pointing to number 1 cyl on compression stroke and went count from there.

 

just checking. i would clean the filters. to me it sounds like you are sucking air somewhere/not getting flow to the pump.

when i am in a hurry to get things running i somehow always switch 6 and 5 on the distributor takes me about 5 minutes to figure out my fuckup

 

Yeah, it has to be something so ill prob start over somewhat and start rechecking some stuff. Only thing that makes me scratch my head is that it seems to run flawlessly for about a min or two, then start going crazy. Makes me think my closed loop is screwed up. If i get some time over thanksgiving im gonna force is to run all time open loop since my maf transfer map is perfection and just see what happens.

Thanks everybody,
Mark

 

i had a similar problem as yours on a carb'd car i put together about 5 yrs ago.when it was all said and done i pulled my timing cover off to find my cam pin sheared...just something to keep in mind. i understand with all the efi it could be a sensor issues...but it may be wise to hook up a vacuum gauge and see what it reads when the car starts missing, goodluck either way hope you figure it out.

 

the fuel press fluctuations are because of vacuum...you removed the hose which took vacuum away from the regulator and pressure went up to around 50 and stayed pretty constant...fuel pressure regulator is ok...I'd say

you have a vacuum problem....either caused by vacuum or causing bad vacuum.

check for vacuum leaks, primarily on things which operate after warm-up and cranking.
IAC on the TB
EGR

also, check your o2's
TPS voltage

are you recirculating from a bypass valve back to before or after the air meter?