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View Full Version : Very poor idle quality, can't tune out the surge. Suggestions?



Blown353
08-11-2006, 07:40 AM
OK, have a idle quality & tuning question.

I just did a FI changeover on a friend's road race Mustang. A little background:

The engine is a 402. I don't know the exact cam specs but it's a solid roller running about .740/.730 lift, high 260-something duration @ .050, 106 LSA. 13.7:1 SCR, aluminum block, heavily massaged Brodix aluminum heads. In a word: freakin' cool in a car that weighs about 2500#, dry sump, jerico 4-speed crashbox, flared fenders and 275/315 Hoosiers on the corners, TCP suspension.

When I was called in to assist the car had a Weber-based IR setup converted to EFI with 36# injectors. The stacks & blades were way too small and the engine was out of air at about 5000 rpm (which was good because it also ran out of injector at the same time so the "restrictor plate" IR setup saved the engine.)

Because of the prohibitive cost of reworking the Weber-based IR setup to be able to feed the engine enough air we converted it using a Victor EFI manifold, Accel 1500 cfm throttle body (a problem piece I will never use again, but I went with it at the request of the owner), 55# injectors, FAST ECU in B2B mode. No IAC currently. Fuel system consists of a Fuel-Safe cell, Aeromotive A1000 pump, 10 micron filter, Aeromotive regulator non-referenced and set at 45 PSI.

I tuned the driving and WOT areas of the map in short order and it runs great but I cannot get this thing to idle worth a damn, it surges badly from 1300 down to 400rpm where it nearly dies then "catches" itself and flares back up. It does this on a period of about 10 seconds. Given the cam specs I don't expect a perfect idle but I was expecting it to hold a fairly steady idle in the 1300rpm range.

With the IR setup it idled steady at about 1200-1300 rpm. I know an IR setup can really tame a cam with a lot of duration and overlap but the idle quality of the new single plane is nothing short of terrible and if I want to get rid of the surges I have to bump it up to the 2000-2200rpm range.

Here's the behavior: the engine will idle at 1300 for about 8-10 seconds, then it seems to load up and the RPM's dip way down to 400 or so, then it catches and revs back up with a little puff of black smoke. My first thought was fluctuating WB02 corrections causing the idle speed surge but it will still surge just as badly running open loop. In the 1300rpm range I've tried making it very lean and very rich and all A/F in between; no matter how much fuel I give it, it still does the surge to 400 rpm every 10 seconds or so. It is not MAP AE or anything like that dumping extra fuel from manifold vacuum fluctuations (checked that) and the throttle plates aren't fluttering. I've tried enabling timing trim @ idle and it doesn't help things at all. I've also tried more and less timing at idle to no avail, still surges like crazy and in the same way.

When the car is idling @ 1300rpm between surges it's pulling about 10" of vacuum which should be plenty of signal for the ECU to maintain idle quality.

Any other thoughts? I was going to try setting it up Alpha-N tonight and just letting it idle to see what happens but my hunch is it will still surge. I will also check everything again for vacuum leaks that could be causing the problem.

Trying to get this sucker ready to go playing up at Thunderhill this weekend.

Thanks in advance...

Elusive R
08-11-2006, 07:48 AM
You're way out of my league, but I'll try anyway - is there any way you can get an IAC on it? At the very least, an IAC might lessen the surging somewhat. My ZZ4 acts the same way when I have mine in closed loop, but mine's trying to take out fuel to the point that my injectors basically shut off.

Ryan

Blown353
08-11-2006, 09:15 AM
The IAC is currently not connected because the previous IR-manifold used a GM screw-in type IAC and the new Accel TB has a o-ring type IAC; the connectors are different between the two styles and he didn't have the right connector. He's trying to scrounge one up for me today.

Given the high RPM this thing idles at I don't expect the IAC to help much (it can only bypass so much air) but it might minimize the surging a little bit especially if I make it aggressive on the PID parameters.

Which leads me to another question: what's the pinout configuration on the inline connector o-ring type GM IAC compared to the screw-in type with the square 4-pin connector? I'm not 100% certain and would like verification...

camcojb
08-11-2006, 12:24 PM
What is the minimum throttle setting like? Idle timing? Fuel pressure and a/f stays steady?

Are you sure there isn't a vacuum leak like under the runners, etc.? Does the throttle body have front and rear blade adjustments, and if so have you tried getting the front and rear opening even? TPS voltage steady and set correctly so computer knows it's idling? Blocked out the entire map area that it's surging in to control it dropping into some very large/small cells? What is the timing doing, is it bouncing between cells that are quite different than others?

I know you understand all this, just writing the first things that pop in my little brain! By the way, my large cams (270/[email protected]) seem to like an idle a/f of about 12.5-12.8:1

Jody

Blown353
08-11-2006, 01:01 PM
What is the minimum throttle setting like? Idle timing? Fuel pressure and a/f stays steady?

Are you sure there isn't a vacuum leak like under the runners, etc.? Does the throttle body have front and rear blade adjustments, and if so have you tried getting the front and rear opening even? TPS voltage steady and set correctly so computer knows it's idling? Blocked out the entire map area that it's surging in to control it dropping into some very large/small cells? What is the timing doing, is it bouncing between cells that are quite different than others?

I know you understand all this, just writing the first things that pop in my little brain! By the way, my large cams (270/[email protected]) seem to like an idle a/f of about 12.5-12.8:1

Jody

Can't say for sure on vacuum leaks. The TB isn't leaking, the injector o-rings seem to be OK (all brand new and were a tight fit but I haven't sprayed anything on them to check for idle speed changes) and I helped port match and install the manifold and I'm pretty sure it is fine.

Fuel pressure is fluctuating a bit, maybe +/- 2psi, which has me worried. At idle the pulsewidths are so quick that may be causing an issue. I asked the guy to pull and check the filter today. The A1000 is making some odd fluctuating noises so it may be going south-- but we need to try another gauge and do a flowtest before we blame the pump.

When not surging the idle A/F is pretty steady about 13.2:1 which is what it seemed to like. When the RPMs start to drop it goes rich, then leans out when the RPMs come back up.

TPS voltage is rock steady. With no timing trim and no IAC connected right now it really isn't playing into the picture too much for idle parameters (except for AE fuel vs. TPS position/rate, checked those and they're not doing anything silly.)

F/R throttle blades are evenly opened although the return spring on the secondary side is a bit weak (another issue with the Accel TB we had to modify... ugh.)

As far as timing, right now we're treating it like a locked out distributor and have it running 30* everywhere, except 5* on the far left of the table at low RPM for cranking timing. I've tried + and - 15* from 30* in the idle areas to see what that did and didn't change much. Timing light indicates things are OK.

When playing with the fueling and timing of the idle problem areas I blocked out and made changes to the entire area, even dramatic changes-- didn't cure the surge. Tried anything from an indicated 10: 1 all the way up to a pegged 15.9:1. Still surges.

camcojb
08-11-2006, 02:00 PM
How low is the idle pulsewidth? It can only go so low. I've seen it be fixed with changing the injector size in config but do not remember why or when the tuner opted to try that.

Jody

Blown353
08-11-2006, 02:12 PM
Idle pulsewidth is about 2.5-2.6ms IIRC... it was a late night last night.

camcojb
08-11-2006, 02:21 PM
Idle pulsewidth is about 2.5-2.6ms IIRC... it was a late night last night.

That should be fine.

Running out of ideas. Still wondering about a vacuum leak, or maybe severe reversion with that new manifold and cam combo.

Jody

Blown353
08-11-2006, 10:30 PM
That should be fine.

Running out of ideas. Still wondering about a vacuum leak, or maybe severe reversion with that new manifold and cam combo.

Jody

Reversion is a good point... immediately after shutdown if you open the TB and look down there's quite a bit of "wet stuff" down there.

Going to hook up the IAC and check the fuel pump tomorrow as the pressure fluctuates a bit even with the engine not running and just the pump on. Shouldn't do that!

DeltaT
08-12-2006, 04:29 PM
Try the unlit propane torch trick to find any vacuum leaks. Installing the IAC should help. You might try Alpha-N at idle and then switch to closed-loop anywhere above idle, like anywhere with the TPS maybe 5 points above its resting value. However, I tuned a 355 with a solid roller almost that big (256/[email protected], 108LSA) and got it to idle right around 950 with little surging. Didn't have to mess with Alpha-N at all. Timing was about 24' at idle, and quickly ramped up to about 29 by 3000 with no load. Fuel map was smooth in the 4 cells it commonly hit at unloaded idle. AFR was right about 13.7. This was with a Holley 950 Pro and wideband.

I think a steady 30 is too much for the idle and off-idle.

How much is the fuel pressure fluctuating?

How do the plugs look?

Jim

nitrorocket
08-12-2006, 05:01 PM
I might be able to offer some sound advice..... I think one issue you need to take car of first off is to get larger injectors. They are way too small for that setup. from there you need to scale them correctly st 45 psi of fuel pressure. After that you have to get an idle AFR reading to see what it is doing along with timing. Keep idle timing in the mid 20's for advance. From there let us know what it is doing.

Also, it will be very hard to tune for idle if everything is not spot on without an IAC.

camcojb
08-12-2006, 08:05 PM
I might be able to offer some sound advice..... I think one issue you need to take car of first off is to get larger injectors. They are way too small for that setup. from there you need to scale them correctly st 45 psi of fuel pressure. After that you have to get an idle AFR reading to see what it is doing along with timing. Keep idle timing in the mid 20's for advance. From there let us know what it is doing.

Also, it will be very hard to tune for idle if everything is not spot on without an IAC.

The injectors are not too small. He has 55# injectors. They'll support nearly 800 HP on a naturally aspirated engine with a safe 80% duty cycle.

Jody

nitrorocket
08-12-2006, 08:42 PM
My bad, I saw Procharger at the bottom of his sig and thought he was boosting.


Sounds a little lean at idle, most rich idle setups will idle well, but rich, unless WAY overly rich.
Get a wideband on there and check the idle.

Blown353
08-12-2006, 11:03 PM
Solved the problem today. I'm a dumbass. LOL.

I said there wasn't any MAP AE fuel being added... guess what, it was the MAP AE. I thought I had fixed that parameter but I fixed it during an "offline" session and neglected to upload it to the ECU. Because of the large cam the vacuum signal at idle is just choppy enough that it was adding quite a bit of AE fuel (base PW at idle was about 2.5 ms and it was adding up to 2.0 ms of MAP AE fuel) which was causing the thing to load up really bad and cause the surging.

Tweaked the MAP AE A little bit and increased the MAP filtering a little bit more and now the thing has a steady 1200rpm idle @ 14:1, down to 1000 if I want. Also got the IAC working today which eliminated the occasional stalls when kicking the clutch in and coming to a stop.

The fuel pump was also taking a dump. It would not build more than 35 psi pressure this morning and sounded terrible. Luckily he had another A1000 as a spare, I put that in and the fuel pressure stayed steady. The other pump will be going back to Aeromotive for a rebuild.

Also got the Accel TB working good today (finally), had to take it apart for some more polishing and had to add a heavy return spring on the secondaries as they would stay partially sucked open when returning to idle and hang the RPM's at 4500.

The car is a total animal (spins the 315 wide Hoosier slicks in 3rd and 4th gear with 3.70's with ease) and will be up at Thunderhill tomorrow for some practice time at the NASA event. Unfortunately I can't go, too many other things I need to take care of here that I've been putting off all week because I've been down at the shop working on that car.

I'll tag along to the next track event and get some seat time in. :3gears:

FYI, here's a couple older pictures of the car.

http://www.totalcontrolproducts.com/vehicles/tcpracecar/main.html

Quite a bit more done to it now.

I now have a very bizarre urge to put a Jerico in my car. I don't know if it's the ungodly loud gear whine or the crunching of the dogs as you slam the shifter as fast as you can, but the silly thing is addictive.

camcojb
08-13-2006, 08:19 AM
Good deal Troy. Overlapping things can be frustrating. I remember having my throttle follower ramped up too low in the rpm scale and holding my idle speed up; unfortunately I checked many things before looking at that one!

I think I've seen that car at TCP in Elk Grove when they were there.

Jody