Monster Problem!

I am having a problem getting the Ford 5.0 in my Monster Miata to hold a steady idle. I have searched all of the 5.0 forums and gone through all of the steps that they suggest to set the idle, but nothing seems to work. Most of the posts deal with lack of air going through the IAC. My problem seems to be too much. I can't get the idle to hold steady below 1500 rpm. Any attempt to go below that and it will "hunt" and then die. The motor has an e303 cam, Trickflow Twisted wedge ported heads, Trickflow Streat Burner intake, a 70 mm Throttle body and 30# injectors w/ matching MAF.

I know that the e303 cam likes to idle at about 900 rpm, but I can't get close to that without lowering the fuel pressure to 28 - 30 psi. It will also run fairly well on the stock 19# injectors, but both options are limiting the power potential of the motor. There are no vacuum leaks that I can find.

Other than swapping in an LS1, what should I do?

you sure there are no vac. leaks with the bigger injectors? sounds like you're getting air in somewhere either between the meter and the throttle, or theres a vac. leak

Are you sure your injectors are capable of a small enough pulse width to allow a proper idle? The fact that you can get it down by lowering the fuel pressure indicates too much fuel when you have the problem, no?

For one, everything I've read says the alphabet cams are crap, especially paired with kickass heads like you have.

For two, try this: ModdedMustangs - 5.0 - Idle reset

I am pretty sure!

I went through all of the vacuum connections with starting fluid to check for leaks. It has also had this same issue through two sets of heads, two sets of upper and lower intakes and 3 throttle bodies!

are you sure the iac is in spec?

In reply to ReverendDexter:

I have tried all of the suggestions on that site, and still come up empty! The idle will not set low enough to allow me to make any other adjustments without lowering the fuel pressure.

Hey, lets see some pictures of this monster. Do you still have the stock EGR system installed? How are the heads and crank case vented?

What's your timing?

In reply to bravenrace: No I am not sure that they are capable of a small enough pulse. (and I am not sure how to find out!) I had the same problem with 24# injectors, (before and after the Trickflow heads) and on the Dyno I was very close to maximizing their capacity.

The only photos that I have available are posted in My Garage. (not great photos.)

The timing is set at 10 degrees. The IAC is a brand new replacement of another brand new unit, just in case, because that was the only part that had been on all of the configurations that this has gone through.

This is the engine with the 24# injectors, not that you can see them!

Oh well.... That didn't work! Can I post a photo from the "My Garage" section?

You said you've had this same problem with 2 sets of head, 2 sets of manifolds and 3 throttle bodies, but you can correct it with lower fuel pressure or smaller injectors. As Strizzo and Bravenrace said, this implies its a fuel problem, not an air problem. Have you measured your A/F ratios? If it idles well with smaller injectors or lower pressure, I'd bet that your large injectors are putting too much fuel into the engine at low RPMs, like Bravenrace said, and it will show very rich A/F ratios at low RPMS with standard fuel pressure and large injectors. When you put in the 19# injectors are you changing the tune in the computer to compensate for the smaller injectors or is it still set for the big injectors? Have you tried a different tune or a different computer to see if the problem goes away? Who created your tune - was it done with your car on a dyno by a pro tuner, a mail order service or did you do it yourself? Is this a speed density of MAF engine? If MAF have you tried a different MAF or cleaning your current one (especially if you're using a K&N or other oiled air filter)?

Bob

How do the plugs look?

I am using a stock computer with a Painless wiring harness. It was Dyno tuned, with the 24# injectors, but the idle problem existed before and after the tuning! It is a Mass Air set up, and I have used MAFs calibrated to each set of injectors. ie I have a 19#, 24# and 30# MAF.

Plugs are also new, but I replaced them just in case. The old ones didn't look bad. Neither lean or fouled.

EGR has been removed. The heads vent from the oil filler tube into the top of the TB, and the PCV vents into the upper intake if I remember correctly.

Are you certain about the idle speed? Verify with another tach.

Who "tuned" the computer?

What base pressure are you starting at? What size feed and return lines? What fuel pump are you running? Volume?

The last E303 cam I ran I used -8 aluminum feed line, -6 return line, an Aeromotive A1000 pump with a standard Aeromotive rail mounted regulator. Base pressure was 42lbs, Idle was pegged at 950rpm on a .030 over 5.8L with Edelbrock Performer RPM heads, worked 5.8L Lightning base and a box upper. Livernois burned the chip and did the tune after assembly and I think they used a Superchips programmer.

Yeah, The idle speed is the same on the tach, and my timing light.

Started with 42 -43 psi fuel pressure, It will idle (sort of ) at 28 -30.

The fuel lines are stock Miata up to the engine bay and then stock Mustang for the last 2 feet. The lines are the same size, I just used pressure fittings to make the connection. I am running the stock Miata in tank pump, with a BBK piggyback pump in line.

It was tuned by a local Dyno shop that specializes in Mustangs, but that was done before the Heads and intake were added, but it was done with the 70mm TB and 24# injectors and MAF.

Did you check the block deck and intake deck(?) for flatness? I was thinking, aside from excessive fuel flow, you might have block warpage. I know it's a bit out there, but, two sets of heads, intakes, and 3 throttle bodies, you either have a problem endemic to that block (warpage under heat leading to vacuum leakage) or you've missed something small that's hasn't been touched during all the parts changing. Are there intermediate injectors between the two you could get your hands on to try and see if there's any change? This makes changing a carb jet look so easy.

I didn't check the deck for flatness. The engine was a re-manufactured long block bought from Advance Auto, so it does have questionable parentage.

Thinking out loud here, but because of the Alternator location, it is difficult to see the timing pointer. What would be the consequences of a couple of degree variation in timing? If I am off of 10 degrees, is isn't much!

Are you running a SD or MAF map sensor? They look the same but do not work the same.

What ECU are you running?

What brand meter are you using?

How is the intake tract before the maf meter?

I ask because some meters need a certain amount of straight airflow before the air enters the meter otherwise the airflow will not hit the sample tube correctly and cause wierd idle issues.

Try rotating the meter so that the sample tube is sitting in different postions and see if the idle clears up.

Fuel pressure should be 35 psi at idle with the vacuum line connected and jump to around 42-45 with a blip of the throttle.

You do not use FP to adjust idle on a EEC4 system.

If the meter sample tube is correct for the injectors the EEC will not have a problem with bigger injecters so I highly doubt running the bigger squirters has anything to do with it.

Nothing wrong with the E/B/F cams. They will not yield the same results as a custom ground cam but they are not "junk" and will work fine.

If the timing was that far out I would figure that the dude tuning the car on a dyno would have figured that one out.

In reply to CaptainSpaulding:

It is MAF. I am running the stock computer that came with the MAF conversion kit.

The intact tract upstream of the MAF straight for about 9" before the MAF. The current MAF is a Summit label, and is calibrated for 30# injectors and a cold air intake. I have also tried a Granatelli MAF.

Fuel pressure is set at 28 psi with the vacuum line connected. I am not sure what it increases to under load. It won't idle above that pressure.

What MAf conversion kit are you using? If it is the Ford racing kit you must use a stock 19lb meter and the Ford racing computer with 24lb squirters.

Yeah that sounds wierd dont it.

The older FMS maf conversion gave you a cobra computer calibrated for 24s and a bigger meter calibrated for 19s as the computer made the adjustement for the bigger squirters not the meter.

So the MAP sensor that is usually mounted on the fire wall is not a MAP sensor but a BARO sensor for a MAF car? You should not have a vacuum line to the BARO sensor. A SD car with the MAP sensor will have a vacuum line ran to it.

No vacuum line to the EGR! Did you remove the EGR valve and if you did how is the block off plate? No leaks?

The FP should be at 35 or so at idle.