Fuel Issue?

Jared Hess · May 11, 2015

So I'll start with my setup 306 with pro comp heads, 1.6 rr, x cam, cobra upper lower, 24lb injectors, 75mm tb, egr delete, cai, stock 5.0 maf, cobra computer, stock dizzy, stock fuel pump, stock regulator, stock rails, New o2s,new fuel filter, these are all the things I think would be relevant to my issues.
Now my issues are starts fine most of the time sometimes have to cycle the pump to start then idles semi rough and never goes through high idle routine idles sometimes for 5 mins then shuts off doesn't stumble just dies, but to get to fire again have to cycle key like 5 times and will keep doing this. It doesn't always happen but 90% of the time. You can keep it running if your in the car to tap the throttle (acts like a cold blooded carb). Also occasionally pops threw the intake when you tap the gas.
Throttle is super touchy have to slip the clutch so I'm not laying rubber. It also bucks when cruising barley touching the gas which I believe to be because of not using a cobra maf with the right transfer and size, but I don't think that is causing all my issues.
My timing is good my fuel pressure is where it should be. Could this be fuel pump? Tuning issues? Dizzy? Please help this is making me want my carb back.

Jared Hess · May 11, 2015

I also forgot to mention seems to run great besides the mentioned issues no missing or cutting out under load or wot.

2000xp8 · May 12, 2015

Buy a cobra meter, better yet, lose the cobra computer, get a pro m bullet calibrated for 24's and get an a9l.

You can't expect to trouble shoot a car with mismatched parts. The meter helps deliver the correct amount of fuel, so no surprise you have fuel issues.

The cobra setup was crap, that is why I suggest going back to the stock computer.

Jared Hess · May 12, 2015

Yea I've thought about it but at this moment I don't have the money to switch like that well the wife won't allow it neway lol. But the cobra setup worked good on another car just I didn't get the maf too at the time didn't know there was a difference. Finding the right cobra maf is hard but I did see late model is carrying one now I believe pro m running the cobra transfer. But I just can't see blaming everything on that. I saw some ppl saying maybe the dizzy module but I think my symptoms lead more towards fuel. I shoulda just stayed carb lol.

2000xp8 · May 12, 2015

Not saying your issue isn't multilayered, but you have a setup known not to work right. No problem is going to be free to fix.

BTW, there is a cobra computer with bids on it on ebay at $185 (and not over yet).
Sell the cobra on ebay, then buy an a9l. I think autozone has them refurbed for $175+core. You could probably even turn it in as the core.
Then get $100 together and buy a used pro m bullet.

Or get the stock computer, leave the stock meter and put 19's back in it. This fix could be close to free if you buy and sell. I've seen TFS top ends run fine with 19's and stock meter, so i'd guess lesser setups will too.

If you aren't going to fix the computer and mass air situation, you might as well fix nothing.

For the record, fuel pumps usually work or don't.

Jared Hess · May 12, 2015

Yea that makes sense I might give that a shot before anything else I just figured it wouldn't make a huge difference I've tried to be careful with matching stuff and it seems like other people can just throw anything on with no issues lol. I don't think I could get away with 19s tho without working them hard and it deff deserves a bigger maf I would think, I have more mods than listed but just put the things I would think concern my problem. That's why I came here cause I'm new to the fuel injected seen. And thanks for Ur feed back by the way, maybe I can get the credit card out till I sell the x3z she's my dd.

Jared Hess · Jun 3, 2015

So I finally got a cobra maf and fixed almost all my problems but one.. the car still shuts off while idling. This is how it goes car starts fine then after a couple mins just dies sometimes stutters but most of the time just dies. Then the weird part cycle the key to the run position and the fuel pump comes on..turn the key farther to turn it over and it won't start when you leave off the key (back to the on position) the fuel pump should run again but it isn't. After a couple times of cycling like this you can finally here the pump come on and it starts with the next turn. The thing that baffles me is it doesn't shut off while driving only when idling or when you go to a store and come back out it won't start and you gotta keep cycling the key to the point where the pump kicks on after you leave off from cranking. Again the pump primes when you go from off to on but after you turn farther to crank and leave off the pump should prime again and it doesn't. This problem is random also it doesn't do it every time but most of the time. Please any ideas!!???

jka · Jun 3, 2015

you may have a bad ignition switch.

Jared Hess · Jun 3, 2015

Those were my thoughts because I had that before but it's only when idling not driving if it was that or the box losing connection it would happen when driving to I would think.

jrichker · Jun 5, 2015

As suggested, replace the ignition switch.
Recall on Ford Ignition switches:

Revised 7-June-2014 to add Torx bit picture and source. Also added replacement ignition switch wiring pigtail picture, part numbers and sources.

Some of the symptoms of ignition switch problems are things that don’t work or are intermittent like radio, turn signals, wipers or heater.

There was a FREE recall on Ford ignition switches. They overheat and sometimes catch fire. That burns up the steering column and sometimes the car interior. Since this is very old information, you may not be able to get the switch replaced for free anymore. The auto parts stores sell the switches for $13-$15.

While you are working on the switch, check the wiring and connector closely. A replacement connector with new wiring pigtails is available from most auto parts stores

AutoZone and Advanced Auto Parts have the same Part Number: 434 - may have to order, not always in stock

Advanced Auto Parts alternate part number: PT5534

Saleen0679 was nice enough to dig this up for us awhile back: Replace a 1979-1993 Ignition Switch Assembly

Torx bit set from Advance Auto Parts

Autocraft torx bit set – have small hole in tip for tamper proof screws.
Part No. AC571/W1386 Cost approx. $12 +tax

Diagrams courtesy of Tmoss & Stang&2birds

Ignition switch wiring

Fuel, alternator, A/C and ignition wiring

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring Mustang FAQ - Wiring & Engine Info Everyone should bookmark this site.

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

O2 sensor wiring harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangO2Harness.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pin out
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

87-92 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang87-92 PowerWindowWiring.gif

93 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang93PowerWindows.gif

Visual comparison of the Ford Fuel Injectors, picture by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/Ford_Injector_Guide.jpg

One problem is that the stock fuel pump isn't big enough to supply all the fuel needed for 24# injectors.
Copied from the FORD RACING PERFORMANCE PARTS catalog:

PROPERLY SIZING FUEL SYSTEM COMPONENTS

Fuel Pumps
The following information is presented assuming the above information has been taken into consideration regarding BSFC, fuel pressure and specific gravity of the fuel being used. Most fuel pumps for electronic fuel injection are rated for flow at 12 volts @ 40 PSI. Most vehicle charging systems operate anywhere from 13.2v to 14.4v. The more voltage you feed a pump, the faster it spins which, obviously, will put out more fuel. Rating a fuel pump at 12 volts then, should offer a fairly conservative fuel flow rating allowing you to safely determine the pump’s ability to supply an adequate amount of fuel for a particular application.

As previously mentioned, engines actually require a certain WEIGHT of fuel, NOT a certain VOLUME of fuel per horsepower. This can offer a bit of confusion since most fuel pumps are rated by volume, and not by weight. To determine the proper fuel pump required, a few mathematical conversions will need to be performed using the following information. There are 3.785 liters in 1 US Gallon. 1 gallon of gasoline (.72 specific gravity @ 65° F) weighs 6.009 LBS.

To be certain that the fuel pump is not run to its very limit, which could potentially be dangerous to the engine, multiply the final output of the fuel pump by 0.9 to determine the capacity of the fuel pump at 90% output. This should offer plenty of ‘cushion’ as to the overall “horsepower capacity” of the fuel pump.

To determine the overall capacity of a fuel pump rated in liters, use the additional following conversions:
(Liters per Hour) / 3.785 = Gallons
Multiply by 6.009 = LBS/HR
Multiply by 0.9 = Capacity at 90%
Divide by BSFC = Horsepower Capacity
So for a 110 LPH fuel pump:
110 / 3.785 = 29.06 Gallons
29.06 x 6.009 = 174.62 LBS/HR
174.62 x 0.9 = 157 LBS/HR @ 90% Capacity
157 / 0.5 = 314 HP safe naturally aspirated “Horsepower Capacity”

Safe “Horsepower Capacity” @ 40 PSI with 12 Volts
60 Liter Pump = 95 LB/HR X .9 = 86 LB/HR, Safe for 170 naturally aspirated Horsepower
88 Liter Pump = 140 LB/HR X .9 = 126 LB/HR, Safe for 250 naturally aspirated Horsepower
110 Liter Pump = 175 LB/HR X .9 = 157 LB/HR, Safe for 315 naturally aspirated Horsepower
155 Liter Pump = 246 LB/HR X .9 = 221 LB/HR, Safe for 440 naturally aspirated Horsepower
190 Liter Pump = 302 LB/HR X .9 = 271 LB/HR, Safe for 540 naturally aspirated Horsepower
255 Liter Pump = 405 LB/HR X .9 = 364 LB/HR, Safe for 700 naturally aspirated Horsepower

Note: For forced induction engines, the above power levels will be reduced because as the pressure required by the pump increases, the flow decreases. In order to do proper fuel pump sizing, a fuel pump map is required, which shows flow rate versus delivery pressure.

That is, a 255 liter per hour pump at 40 PSI may only supply 200 liters per hour at 58 PSI (40 PSI plus 18 lbs of boost). Additionally, if you use a fuel line that is not large enough, this can result in decreased fuel volume due to the pressure drop across the fuel feed line: 255 LPH at the pump may only result in 225 LPH at the fuel rail.

Jared Hess · Jun 5, 2015

I may try that just to be safe but I thought I read that the cobra pump is the same as the gt so why would Ford use a wrong sized pump for the injectors not arguing and I wanna change it out for something to support other mods anyway just wondering.

Jared Hess · Jun 5, 2015

Also I thought the cobra maf fixed all my other issues but after a long trip today they came back but not as bad I'm getting a bucking issue cruising at anywhere from 1900 to 2000 rpm after that it smooths out also a slight miss I think when accelerating easy. The bucking is really bad and always seems to happen when passing a cop through town which results in barking the tires (waiting for a ticket). It reminds me of someone trying to learn how to drive a stick for the first time. In my head im thinking something with the distributer, tps, iac maybe but have never had this issue with anything else when the previous went bad. Also no idle surge which seems to be what most ppl get. I mean it lopes real hard but it's an x cam so I expect that.

Jared Hess · Jun 5, 2015

Maybe a vacuum leak also but I did a smoke test a while back and plugged all my leaks. It's possible I had a small leak that grew up to now but this problem has been there since the beginning. Its really frustrating almost everything is new and the motor might be turning over 200 miles now and I can't figure it out. I MISS MY CARB!!!!!

jka · Jun 6, 2015

Okay the bucking plus stalling and the misfire sounds like a distributor/pickup coil problem.

Jared Hess · Jun 6, 2015

That's what I'm thinking would it be stupid to change out tfi module, cap and rotor, or just buy a whole new dizzy, I'm running an msd ignition box with stock dizzy and coil I want the cheapest route but if the prices would be close I think I could pick up a used msd dizzy or even a new summit for a decent price I've never messed with different dizzys is there a benefit? I know with the ignition I rerouted to stock one day to see if it was an issue and there was a noticeable difference in how the car ran besides the problems they stayed, just saying the ignition helps alot.

jrichker · Jun 6, 2015

MSD stands for "May Suddenly Die". In 14 years and @2,000+ posts I have seen more MSD problems than any other aftermarket parts manufacturer.

Bypass the MSD setup and go back to stock ignition.
Here's a diagram of how the MSD boxes are supposed to be wired.

MSD wiring:

Instead of using the battery negative terminal, attach the heavy gauge black wire to the body ground point by the windshield washer filler.

The battery common ground is a 10 gauge pigtail with the computer ground attached to it.
Picture courtesy timewarped1972

Jared Hess · Jun 6, 2015

So you don't think I'm benefiting from the msd

Jared Hess · Jun 6, 2015

The car seemed sluggish with the stock ignition. I mean I can try it again as I've changed some other things. I did have a problem with the same ignition in another car I had it mounted in engine bay and it would get to hot and cause a miss passed 4000 but now it's mounted in radio slot and stays cool.

jrichker · Jun 6, 2015

Jared Hess said:
So you don't think I'm benefiting from the msd

Not at all. The stock ignition is good to 400-450 HP when all the parts are working like they should.

MSD's quality control and parts quality is pretty close to the bottom of the list. Bypassing it is simple and will reduces the number of variables in your troubleshooting suspects.

Jared Hess · Jun 6, 2015

jrichker said:
Not at all. The stock ignition is good to 400-450 HP when all the parts are working like they should.

MSD's quality control and parts quality is pretty close to the bottom of the list. Bypassing it is simple and will reduces the number of variables in your troubleshooting suspects.

Ok I'll give it a shot it's funny how since everybody does something it seems like a must.

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