GT35R turbo for 3.4L? - Page 4

forte500 · 12-12-2011, 03:47 PM

hmmm....it happened very very randomly (ie. noticed on a couple hard downshifts as described) and boost was not at full (.8 Bar) and was only momentarily - and then pulled hard to full boost and max RPM's. The motec has expander module with direct fire to 12 plugs...this should be sufficient?? What were the symptoms of "ignition breakdown"?

911TT33 · 12-12-2011, 03:51 PM

Engine hesitation as boost built up quickly to max... Once the hotter ignition was installed, never had a problem with hesitation. The charge air would essentially blow out the spark from the OEM ignition.

Doesn't sound like you have that issue though, with the DFI setup.

MikeD930 · MikeD930's Garage

Hmm...what brand and type of spark plugs are you using? I'd go with simple copper type plugs and stay away from multi tipped spark plugs (i.e. two or four tang over an electrode). Also, make sure your plug gap is not excessive.

JBurer · 12-15-2011, 07:25 AM

Frank,
Ignition breakup usually occurs under high load, high rpm - and unlikely in the scenario you're describing, boost pressure, ignition system you have, etc.

What it sounds like to me is an overly rich condition caused by too much throttle accel fuel. Are you setup to log wideband O2 on the street? Should be easy to confirm.

Quote:

Originally Posted by forte500

hmmm....it happened very very randomly (ie. noticed on a couple hard downshifts as described) and boost was not at full (.8 Bar) and was only momentarily - and then pulled hard to full boost and max RPM's. The motec has expander module with direct fire to 12 plugs...this should be sufficient?? What were the symptoms of "ignition breakdown"?

Tippy · 12-15-2011, 09:28 AM

This happens to me on the factory Mototronic; if I stab the throttle sometimes after a high-RPM decel, the engine does not respond a lick!

Never understood what was going on.

forte500 · 12-15-2011, 05:11 PM

Ok...so all 12 plugs are new single-trode with .023 Gap. Car was dyno tuned with wide-band O2 sensor and street tuned. We went through all the connections, voltages, etc....carefully and found no issues. Motec data logger shows no flags/errors. I am wondering if it could be an intermittent Expander or a ghost in the Motec? It's seemingly random so might be something loose that shows up on hard accel or decel??

Using the Motec M48 - which I understand is robust, but the logger software is hard to work with/check.

Raceboy · Raceboy's Garage

I would check acceleration enrichment settings in Motec ECU if the engine stumbles when pushing the throttle during overrun.

JBurer · 12-16-2011, 05:37 AM

Frank,
If the problem is repeatable, it is likely a throttle fuel accel setting in your tuning file that needs to be adjusted. I've owned/had built half a dozen tuner cars over the years and there is always a fair amount of fine tuning that needs to be done off the dyno.

Dyno tuning is great for a very narrow band of cells that are hit during WOT and other's that you'd see during cruising. The transition cells (accounting for probably 75% of the map) can be roughly approximated from the dyno - but are typically dialed in further from logs from your normal driving. You can't physically hit all the load points the car will see on a chassis dyno.

Your tuner did the right (aka conservative) thing as it sounds like he left these transition cells on the rich side.
Best,
John

Quote:

Originally Posted by forte500

Ok...so all 12 plugs are new single-trode with .023 Gap. Car was dyno tuned with wide-band O2 sensor and street tuned. We went through all the connections, voltages, etc....carefully and found no issues. Motec data logger shows no flags/errors. I am wondering if it could be an intermittent Expander or a ghost in the Motec? It's seemingly random so might be something loose that shows up on hard accel or decel??

Using the Motec M48 - which I understand is robust, but the logger software is hard to work with/check.

forte500 · 12-16-2011, 07:13 AM

John, seems logical but why would the momentary hesitation and drop in Tach (to 0) while driving/accelerating in 3rd. In other words, on one ride - it did it when accelerating in 3rd gear. A brief (felt like ignition cut) hickup and then okay until redline. Couldn't replicate.

Think you could see it in the motec data if it was rich condition? I couldn't see it.

JBurer · 12-16-2011, 07:28 AM

Frank,
I didn't see you mention the Tach drop to 0 in your initial post. That certainly does change things. I've only seen something like that as a voltage regulator was going bad... but afterwards the idle and tach would act erratic.

I don't see how hotter plugs could solve a problem like that... sounds like an electrical issue to me.

You'd definitely see a sub 10 afr on the datalog. Are you able to log ignition advance and voltage?

Quote:

Originally Posted by forte500

John, seems logical but why would the momentary hesitation and drop in Tach (to 0) while driving/accelerating in 3rd. In other words, on one ride - it did it when accelerating in 3rd gear. A brief (felt like ignition cut) hickup and then okay until redline. Couldn't replicate.

Think you could see it in the motec data if it was rich condition? I couldn't see it.

forte500 · 12-17-2011, 01:14 PM

Just came back from test ride.... I was able to repeat the problem.....every time I would downshift from 4th to 3rd (i.e. taking off ramp) and immediately get back in the gas (start to build RPM/Boost) - there would be a significant hesitation, tach would drop , and then a huge backfire - and then the car would resume boost and RPM like normal.

When just accelerating hard up through the gears - no problems at all. Just when doing the highspeed downshift and then getting back on it. Strange?

Other than that - car runs amazing with no hesitations and is very responsive at all loads and RPM ranges.

911TT33 · 12-17-2011, 01:31 PM

Sounds like a very lean condition during a fast load transition?

Your tuner should be able to replicate on the dyno whilst monitoring the maps and AFRs etc?

forte500 · 12-17-2011, 01:34 PM

Lean? I would have guessed rich due to the backfire

JBurer · 12-18-2011, 08:21 AM

Did you log the drive?

forte500 · 12-18-2011, 08:51 AM

John, I did and am looking over the data now..I plotted the RPM vs. Throttle Pos vs. MAP......I am looking for the pt at which the TP is WOT and the RPM is flat (i.e. where the blip occurs, followed by backfire). It was very noticable, like a Rev limit was hit and seemed to last at least a second - so I should be able to see something. I am not familiar enough with the software to know the flags...I wish some error codes came up??

I also sent to my tuner - and he didn't see anything either - but we must be missing something?

JBurer · 12-18-2011, 01:26 PM

Frank - I'm not familiar with MoTeC's sotfware, but there should be the ability to overlay O2 with the plot of RPM/TPS/MAP. What's the air/fuel ratio as you see the throttle % increasing during that particular part of the map?

Do you notice the blip as you are rapidly opening the throttle, or is this a second after throttle is 100% and boost is ramped up?

forte500 · 12-18-2011, 03:46 PM

John, I will post a screen shot tomorrow with an overlay of O2 as suggested.

It happens after I downshift and a second or two of WOT as the boost and RPM's are rapily climbing - and then it bucks, tach drops and backfires really loud. Then, if I lift off the gas (natural reaction as it's backfiring), and get back in it - it's fine to redline and full boost.

Think of a scenario where your racing someone, and need to drop a gear to hit the boost sweet spot. It does it everytime ONLY in this scenario.

Tippy · 12-18-2011, 04:06 PM

The fact your tach drops to zero and the backfire makes me think you are having a momentary drop out of ignition.

What is causing the condition? That's to be determined.

JBurer · 12-18-2011, 05:11 PM

Frank,
If you've already hit 100% TPS prior to the backfire, and you're not noticing this anywhere else with rapid throttle changes, it doesn't sound like throttle enrichment is the problem.

Hopefully your tuner will be able to zero in on the problem, if you can duplicate the situation for him in the car. I've been using aftermarket standalone ECU's for many years now and I've never experienced anything like you describe.

By the way, noticed Tippy's comment earlier about experiencing this with the factory ECU. Do you still have any of those stock components in the car?

Tippy · 06:07 PM

JBurer, could the TPS going to 100% and switching from off-boost ignition parameters in the maps to the on-boost ignition parameters transitioning cause a hiccup?

Thinking out loud here.....