Ok, I need the help of the experts here. As some may know, I've been tuning my dads topend ported (including heads) ZR-1 in earnest lately and have come across a really unusual problem that I've never experienced before (and I'm a mechanic for a living). At approx 3800-4000 rpm, the engine violently cuts out for less than a second, and then recovers. This only happens as I'm throttling into it (approx 60%) as I transition through that rpm point. If I'm full throttle before that point, it does not happen. According to my Datamaster logs, the injector pw drops to 0 when this occurs, which due to the speed of the sampling, is just one frame. None of the other scan data shows anything unusual when this occurs. It's fully repeatable and only occurs under the specific conditions above. Thinking that I may have introduced a glitch in the prom through my many revisions, I burned a stock AYBK image and installed it, fully expecting the problem to go away. Well, it didn't. I'm currently leaning toward the ECM, but as we all know, they are as rare as hens teeth. The ECM that is currently in the car is an AcDelco reman unit that we installed eight years ago to correct a very obviously bad ECM at the time. Up until now, there have been no indications of any problems. It's possible that the problem has always been there and we've never satisfied the conditions to make it happen until now, as I'm driving it a bit differently than normal to get more data points, but I don't know for sure. Since this isn't an ECM that I can just pickup at the local Kragens for 100$ I'm kinda stuck. I'd like to try a known good unit for testing, but that would require a very generous person that is local, so that probably wont happen. I'm not a parts swapper type of diagnostician, but I believe I'm at that point. Does anyone have some insight and/or a spare 1228331 that they'd be willing to loan out? I've gotta correct this issue as it's almost a safety issue as when the power comes back on, it quickly breaks the tires loose. I'd hate for that to happen to my dad in a turn! BTW, I've been able to get this to happen in both second and third, and would likely get it to happen in first as well if it would hold traction. Help
Scott

 

Mine did that when the fuel pump for the 2ndry went out. Test pressure at the rail by pulling the fuse. 2 fuel pumps on the Z.

Just a thought

LGAFF
92 ZR1
#234

 

Thanks for the suggestion, but it's much too immediate to be a fuel starvation problem. It feels as if you turned off the ignition for a split second then back on. Other than this problem, full throttle performance is excellent all the way to 7300rpm. I did check both fuel pumps six moths or so ago however, while tracking down a different issue.
Scott

 

I don't think its the ECM. What are you using for a bin editor? Took a look at a stock AYBK bin (assuming yours is a 90?). There's a constant for Port Tthrottle to Sec. Inj Delay. Stock setting is .3sec. Todd would be more accurate on this, as a SWAG, you might try changing that to 0.
Interesting you mention 60%TPS because that the Opening Point for PE at 4000rpm in the stock bin. So it sounds that as long as you are below 60% TPS, the Secondary Inj. ON is delayed by.3sec. Above that it overrides the delay.

 

Good ideas. It is a '90 and the constant you mentioned was set to 0 in the modified bins I had been using. I noticed the same thing about PE and at one point I had the Secondaries set to coincide with PE (the mechanical secondaries are actually removed). This was my strongest suspect area at one point so I set the Secondary opening point to stock as a test. No difference. The thing is, putting a stock bin in there didn't eliminate it, essentially ruling out something in the modified bin I've been using. It really has all the earmarks of a software glitch which is why I was sure the stock bin would have cured it. I am using Tunerpro that came with my Moates RT system (all of which works well). It is possible that something in that part of the chain could be introducing an error as the stock image I burned was done so with this equipment. The next thing I'm gonna do when it stops raining is to try the actual original memcal by itself, complete with the messed up idle strategy.
Scott

 

Any chance the Injectors are firing asynch for that moment? Anything in the log on that?

 

here is a ph number 210 867 6286 . for corey henderson one of the best zr1 tuners out there run this by him .

 

I'm ashamed to admit that I'm not too familiar with asynchronous opperation. I remember some mention of it when I was studing to be a mechanic, but it was never really explained. Where in the log would I check, and what is asynch opperation about? All I know is that the reported PW is zero then it occurs.
Scott

 

Scott,

Its clear the injectors are being "turned off" momentarily. Its like a momentary fuel kill. I brought up asynch because at times the transition between asynch/synch operation causes the injectors to stop momentarily. Looking at the 8EA.xdf for the 90 AYBK I don't see any asynch controls defined.

 

Mine had a very similar problem. Thanks to Mark H. found my map sensor hose on back of plenum was deteriorated with a soft spot and suck shut while cruising and with acceleration sensor input to ecm was dalayed and would shut off engine until loss of vacum, to open hose up with a snap to the driveline that didn't sound good. Your datamaster might show a delayed input when accelerated if it's something related to the map. Good Luck.

 

That sounds like exactly how it behaves when the car has an active code thrown. I'm a rank novice on fuel injection, but I know enough to have been through the tuning process on ONE motor that I actually built.

I just thought I would share one experience I had when my dad and I took our texas to vegas trip in my ZR1

The car threw code 61 it was the secondary vacuum solenoid that was bad. I think because I drove through the north texas dust storm from hell It destroyed the solenoid but back to the point...

I know you must know this, but when the code was active, the car behaved exactly as you describe in your first post...you guys know a lot more than me about this stuff, but haven't you ever been in your shop trying to figure something out for hours and someone like your wife walks up and sees it immediatley and calls you a moron?

I wish I knew more.

Rick

 

if a code 53, 61, or 56 is set, a 3000 rpm fuel cutoff is enabled.

 

Just so everyone knows, there are no codes stored before, during, or after this problem happens. The next step will be the installation of the original memcal, probably in the next day or so. I REALLY appreciate everybodys help on this. I'll have more info soon!
Scott