Mustang EFI stumble – Tuning or manual Timing?

[xcntrk]

I have a slight stumble with my EFI 302 between idle and 1500 RPM. Throttle tip-in in this range gives a little bit of hesitation or stumble. What’s odd is that it only happens with slight throttle, if you stab the skinny pedal down low there’s no stumble. I can replicate this problem since I have a manual transmission by running a gear down below 1500 rpm then tipping in the throttle (maybe 10-20% ). Depending on which gear and how much load is on the motor, it can produce some bucking/pinging which is a clear sign of too much timing advance and detonation! The issue is easily avoidable as I don't make a habit of lugging around my MT gears below 1500 RPM.

So my question; without getting into EEC tuning can I manually adjust the initial base timing to work around this issue? I’m current set at 10 degree BTDC and the EEC is operating correctly with full range of an additional 20 degree advance (tested).

My motor setup is nothing crazy but it’s possible the EEC might need tuning due to the cam used. I don’t have the engine specs but I know it’s a flat-tappet cam and is clearly aftermarket in performance (rumppty rump) ;D

Thoughts?

 

[WheelHorse]

Are you sure there's no flat spots in the TPS sweep around that range? Where voltage drops to zero or goes a little wonky?

 

[KyleQ]

I've run all sorts of crappy combo's on my EFI and never had a stumble like that - check out the voltage of the TPS on a sweep, may be a flat spot.

 

[xcntrk]

I did set my TPS for min and max voltage to ensure they were within the expected voltage range. Everything checked out, but I did not test the voltage throughout the range and can do that. I will admit I am challenged in throttle cable setup. I'm either stuck with super sensitive throttle response but with full range of motion, or I can move to the next adjustment standoff and have less sensitivity (just right) but can only accomplish about 75% throttle range.

But regardless of TPS range, the bucking/pinging at low RPM with load while accelerating is a sign of too much advance. Not sure how that would relate to TPS position...

 

[Viperwolf1]

Make the throttle progressive. http://classicbroncos.com/forums/showthread.php?t=249295

 

[xcntrk]

Make the throttle progressive. http://classicbroncos.com/forums/showthread.php?t=249295

Thanks viper... I've seen this and need to do it, but am delayed in gathering up the hard parts and need a new throttle cable as my existing will be too short. You should consider packing this modification up as a turn-key kit! Vipers perfect EB progressive efi throttle kit! I'd buy that for $50 bucks.. ;D

 

[BroncoKelley]

I had the same problem on my 90 mustang. After replacing the TPS, etc, etc, I found that the mass air flow sensor was the cause. I had a larger 75mm pro-m mass air flow sensor and when I installed bigger injectors I sent that mass air out to be recalibrated. In the mean time, I installed my stock mass air flow sensor and bingo, the problem disappeared! Apparently if you over-oil your K&N filter after cleaning, some of the oil gets on the mass air flow sensor causing problems!

 

[Viperwolf1]

Thanks viper... I've seen this and need to do it, but am delayed in gathering up the hard parts and need a new throttle cable as my existing will be too short. You should consider packing this modification up as a turn-key kit! Vipers perfect EB progressive efi throttle kit! I'd buy that for $50 bucks.. ;D

You can buy replacement inner cable at most hardware stores.

 

[WheelHorse]

I did set my TPS for min and max voltage to ensure they were within the expected voltage range. Everything checked out, but I did not test the voltage throughout the range and can do that. I will admit I am challenged in throttle cable setup. I'm either stuck with super sensitive throttle response but with full range of motion, or I can move to the next adjustment standoff and have less sensitivity (just right) but can only accomplish about 75% throttle range.

But regardless of TPS range, the bucking/pinging at low RPM with load while accelerating is a sign of too much advance. Not sure how that would relate to TPS position...

Or a lean condition with the sharp edges of the CC causing the detonation at low-rpm, higher-load.

Fuel pressure check out?

O2's switching nicely?

MAF clean and not tampered with? Sometimes just rotating the MAF makes all the difference. Watched it on the dyno so I know it's not magazine hearsay.

 

[xcntrk]

Or a lean condition with the sharp edges of the CC causing the detonation at low-rpm, higher-load.

Fuel pressure check out?

O2's switching nicely?

MAF clean and not tampered with? Sometimes just rotating the MAF makes all the difference. Watched it on the dyno so I know it's not magazine hearsay.

The setup is virtually all stock components including EGR spacer and stock Mustang MAF and TB. I did this so I could try and start with a nice stable platform before I started mucking with aftermarket parts.

Fuel Pressure was a concern initially. I read 35psi at idle but it does step up to 40psi when revving the motor. The entire fuel system is new including: tank, pump (walbro), braided lines with AN fittings, hard-lines in the middle. One thing I noticed is that when you prime the system (first turn of the key), it will build the initial 35psi but will then taper off when the pump doesn't stay running. So for example after running the motor if you turn off the key, within a minute all stored fuel pressure will have been lost. I assume this is normal in a recirculating system, especially one with new high flowing lines??

O2 switching? Not sure what you mean by that or how I test. Do you mean closed versus open-loop fueling? I'm currently doing no data logging from the EEC and have no ability too (until I get a chip). Only diagnostics I can do is OBD-1 code reading and the KOEO/KOER tests.

The MAF is 100% OE stock Mustang - but is used and probably 20 years old. It's in good clean shape but probably wouldn't hurt to soak it in rubbing alcohol or other MAF cleaner. One other note on MAF and Fueling, I am running EV6 style injectors. They're still 19lb but are of the newer design with different/better flow pattern. But that should make things better not worse..

 

[76Broncofromhell]

I had the same problem on my 90 mustang. After replacing the TPS, etc, etc, I found that the mass air flow sensor was the cause. I had a larger 75mm pro-m mass air flow sensor and when I installed bigger injectors I sent that mass air out to be recalibrated. In the mean time, I installed my stock mass air flow sensor and bingo, the problem disappeared! Apparently if you over-oil your K&N filter after cleaning, some of the oil gets on the mass air flow sensor causing problems!

This.

They will do all sorts of weird shit if the MAF has oil / dirt on the sensor element. And since most Mustang owners bought into all of K&N's marketing material back in the 90s, it's a pretty solid bet your MAF is dirty and causing this.

Buy some MAF cleaner and spray it through the small hole of the MAF. Be sure to give it time to dry before you hook the MAF back up. Don't use carb or brake clean.

 

[anoblefox]

don't forget to remove the "spout connector" when setting timing!

 

[Viperwolf1]

The setup is virtually all stock components including EGR spacer and stock Mustang MAF and TB. I did this so I could try and start with a nice stable platform before I started mucking with aftermarket parts.

Fuel Pressure was a concern initially. I read 35psi at idle but it does step up to 40psi when revving the motor. The entire fuel system is new including: tank, pump (walbro), braided lines with AN fittings, hard-lines in the middle. One thing I noticed is that when you prime the system (first turn of the key), it will build the initial 35psi but will then taper off when the pump doesn't stay running. So for example after running the motor if you turn off the key, within a minute all stored fuel pressure will have been lost. I assume this is normal in a recirculating system, especially one with new high flowing lines??

One minute is awful quick to lose all pressure. You have a leak somewhere. It could be at a connection in the lines, faulty fuel pressure regulator, or it could be an injector not closing. If you can't find an external leak and it's anything except the injector you could probably live with it. The pump will just have to work a little more.

 

[xcntrk]

One minute is awful quick to lose all pressure. You have a leak somewhere. It could be at a connection in the lines, faulty fuel pressure regulator, or it could be an injector not closing. If you can't find an external leak and it's anything except the injector you could probably live with it. The pump will just have to work a little more.

One minute may have been an exaggeration. I'll time it more approximately to see if there's a real issue here. There's no external leaks as I've inspected repeatedly. I also tested the injectors when I cleaned them as part of the install. This included hooking up to 12v trigger and blowing injector cleaner + pressurized air through them. All injectors engaged on/off just fine. Doesn't totally rule out a leaky injector but should at least lower suspicion.

 

[nat22453]

Every time I have encountered the problem you are having it has been a bad tps. If you have a buddy with a working 5.0 swap over his tps and see what happens.

 

[xcntrk]

I'm going to install a new TPS and clean the MAF. I also picked up the HW for the Viper progressive throttle mod. Just need to install it. Thanks...

 

[airbur]

While that throttle setup Viper came up with is awesome, are you sure you need it? I have around 500HP at the pedal and an extremely sensitive Pro-M MAF and Accufab TB and I don't use the progressive mod.

Viper, you drove mine, was it really that different?

 

[Viperwolf1]

While that throttle setup Viper came up with is awesome, are you sure you need it? I have around 500HP at the pedal and an extremely sensitive Pro-M MAF and Accufab TB and I don't use the progressive mod.

Viper, you drove mine, was it really that different?

You need something to make the throttle less touchy. I recall it didn't feel like the pedal moved at all between idle and break the tires loose.

 

[xcntrk]

While that throttle setup Viper came up with is awesome, are you sure you need it? I have around 500HP at the pedal and an extremely sensitive Pro-M MAF and Accufab TB and I don't use the progressive mod.

Viper, you drove mine, was it really that different?

Yes I definitely need it. I've been messing with the throttle since I finished my EFI conversion and can't get it to where I'm happy. But I do think the throttle cable setup and this minor stumble issue are unrelated. I have a new TPS and MAF inbound, those are the only 2 sensors that are not brand new on my setup, hopefully that will help.