Engine Hiccup at full throttle

[keel]

Got a '93 5.0, under wide open throttle the car sometimes has a little hiccup like a misfire. I know I'm probably pretty close to max duty cycle on my 19lb injectors so I'm wondering if that could be the problem or if it's something else. Thought it was ignition related at first so I replaced the cap and rotor and the plugs but the problem persists. Next up on the list would be the coil.

Car has ported GT40 heads, GT40 intake, Trick Flow stage 1 cam, 155LPH fuel pump, and longtube headers. Everything else is stock (airbox, throttle body, MAF, ECU tune).

 

[gkomo]

Does it make any noises (pops/bangs) or just loss of power? Can it still rev higher after the hiccup or does it fall flat from a power perspective from a certain point/RPM?

 

[keel]

Does it make any noises (pops/bangs) or just loss of power? Can it still rev higher after the hiccup or does it fall flat from a power perspective from a certain point/RPM?

Nope no other symptoms, just loses power for a moment and then continues to rev higher. Feels like the car makes the most power between about 4000-5000rpm and it tapers off pretty quickly after that but I think that is normal for these engines.

 

[gkomo]

Is it the same RPM it loses power at each time or just happens randomly? Since you say it continues to rev higher i wouldn't think it was the injectors, but more something to do with your distributor (TFI or PIP).

My car falls flat (like loss of all power throws you forward in the seat) at 5,200 rpm under load. No weird noises or pops/bangs, just stops. Won't rev higher. I think my issue is my distributor or TFI.

 

[keel]

It's pretty random, sometimes doesn't happen at all. Definitely doesn't fall on it's face like you're describing @gkomo.

 

[General karthief]

You prolly have a loose connection like at the ignition switch or along the ignition wires.
Check key switch, with engine running giggle the key switch and wires to the coil and distributor wires.

 

[LILCBRA]

Is this as soon as you floor it? If so, it sounds like a lean condition in that scenario. Holley carburetors do this if the accelerator pump isn't properly adjusted. If that's the case, I'd lean toward the TPS needing adjusted or maybe replaced.

 

[AeroCoupe]

Have you checked for codes? Even if the check engine light (CEL) is not flashing there can be codes so that is the first thing you should check before replacing any parts.

I feel like a broken record....

 

[keel]

Have you checked for codes? Even if the check engine light (CEL) is not flashing there can be codes so that is the first thing you should check before replacing any parts.

I feel like a broken record....

Sorry forgot to include that, no codes other than stuff related to deleting the EGR.

Is this as soon as you floor it? If so, it sounds like a lean condition in that scenario. Holley carburetors do this if the accelerator pump isn't properly adjusted. If that's the case, I'd lean toward the TPS needing adjusted or maybe replaced.

It tips in just fine when I floor it but if I stay in the gas for a little while then it starts to hiccup/break up.

You prolly have a loose connection like at the ignition switch or along the ignition wires.
Check key switch, with engine running giggle the key switch and wires to the coil and distributor wires.

I'll try this.

It seems like you guys think my injector size is fine for supporting my other mods?

 

[Noobz347]

19s will support roughly, 260 N/A FWHP at 85% duty cycle with a 0.50 BSFC.

At 300 FWHP, you're at 100% duty cycle.

With enough pump and a little bit of boost in fuel pressure, the HP number will go up while the duty cycle numbers come down... To a point, of course.

If you think you're running out of fuel at the very top and have an adjustable FPR, bump the fuel pressure up a pound or two.

 

[General karthief]

t tips in just fine when I floor it but if I stay in the gas for a little while then it starts to hiccup/break up

This does point to fuel injector or fuel pressure issue

 

[keel]

19s will support roughly, 260 N/A FWHP at 85% duty cycle with a 0.50 BSFC.

At 300 FWHP, you're at 100% duty cycle.

With enough pump and a little bit of boost in fuel pressure, the HP number will go up while the duty cycle numbers come down... To a point, of course.

If you think you're running out of fuel at the very top and have an adjustable FPR, bump the fuel pressure up a pound or two.

I've never had the car on the dyno but my best guess is about 300FWHP or about 250 at the tire based on what other people are putting down with similar mods. Correct me if I'm wrong... But it sounds like I need some 24lb injectors to be at a reasonable duty cycle anyway even if that isn't directly causing this particular problem.

 

[Noobz347]

I've never had the car on the dyno but my best guess is about 300FWHP or about 250 at the tire based on what other people are putting down with similar mods. Correct me if I'm wrong... But it sounds like I need some 24lb injectors to be at a reasonable duty cycle anyway even if that isn't directly causing this particular problem.

Yes. If you're at that level then you're in to 24lb injectors territory which of course, opens up other cans of worms.


Do I go 24s and that's all I need?
Do I have other mods on the burner?
Is it better to go bigger now than pay twice?
Can I get away with a "calibrated MAF" and 24s without a tune?
Can I go with even larger injectors without a tune?

If small bump in fuel pressure solves the issue, that's what I'd do until something else dictated the need for a larger injector.

Incidentally, I ran 19 lb injectors up to as much as 70 psi with a blower and an FMU. So, the injectors themselves won't skip a beat with a small pressure bump.

 

[keel]

Is the stock ECU able to compensate for higher fuel pressure so that the car doesn't run rich at idle/low speeds?

 

[AeroCoupe]

MAF car will try and correct +/- 10% on the fuel tables. If you are running lean and it’s maxed out trying to correct a couple of psi higher fuel pressure will help it correct. Those couple of psi should not hurt you down at idle as the ECU is most likely not maxed out trying to lean it out.

One way to find out is bump the pressure, take it for a drive, and read the plugs.

 

[86HO5.0]

You're out of fuel injector, bump to 24's or 30's. Adding fuel pressure will be negated by the LTFT over time and you'll be back to square one.

FWIW--My stock cammed GT40P head setup holds power cleanly until 5500 and doesn't have a noticeable 'sign off' in power until 5700. I'm also running 30lb injectors.

 

[keel]

You're out of fuel injector, bump to 24's or 30's. Adding fuel pressure will be negated by the LTFT over time and you'll be back to square one.

FWIW--My stock cammed GT40P head setup holds power cleanly until 5500 and doesn't have a noticeable 'sign off' in power until 5700. I'm also running 30lb injectors.

Are you running a calibrated MAF?

 

[86HO5.0]

Not running MAF, running Megasquirt.

 

[keel]

I'm going to try an adjustable FPR first since I can pick one up for about $50 just to see if that makes any difference and then I might get injectors and a MAF depending on my results.

Adding fuel pressure will be negated by the LTFT over time and you'll be back to square one.

Can you explain this a little further I don't really know what this means.

 

[86HO5.0]

Long term fuel trim. Adding fuel pressure will cause the ECU to pull fuel over time to correct the richer than expected conditions in everyday driving. It will correct WOT throttle situations as well, ultimately leading to ending up where you started. FPR's are great when you can tune the ECU to the changes in fuel pressure and adjust the fuel trims accordingly. On a stock ECU it's negated.