What kind of things do I need to change for an LT4 HOT cam and my 7730 PROM? Is there a bin on diy-efi for one?

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West Coast GM Shootout 2001!
1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.25 @ 107.18 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-

 

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It's not that easy Kevin. I know I asked that question too when I first got into EPROM burning. You have to test the car, and see what the engine needs. I started by looking at other people's .bins and what they did and went from there.

 

Well thats what I'm asking. Has anyone made a bin for use with an LT4 HOT cam? Is there one on diy-efi.org? It'll be a lot easier to tune my car if I have somewhere to start, other than with my stock 305 5-speed chip.

 

Haven't seen one, but I am sure SOMEONE has a BIN for that setup. I'll post a link if I find one or e-mail it.

 

I'm a little late since I was on vacation, but you can ask Mike Davis (he's on the third-gen and Mid Atlantic F-body lists) since he has a ZZ4 engine with an LT4 HOT cam and has switched to the '730 ECM. He could either e-mail you his latest bin or let you know what he changed. I think his best time is around 12.8 at 108 mph, and now he's looking at replacing the stock heads with AFR's.


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Greg Westphal
'87 IROC 305TPI/A4

 

Thanks Greg!

 

Any luck in finding a 7730 HOT cam chip in the DIY-EFI depository to start with? It shouldnt be too hard to start with the stock chip but if someone has one available it'd be easier...

 

Well I was unable to get a chip from anyone, so I'm stuck using the same chip I used for the ZZ4 cam. The car has 10-11" of vacuum at 700 RPM idle. It idles crappy in open loop but does ok in closed loop. Its showing 2.5mv injector pulse width. The O2 voltage is fluctuating normally in closed loop. If I give it gas and bring the RPMs up to about 1500, everything seems great. It'll have 15" of vacuum, the injectors are at 1.9mv, and it sounds a lot better. But I dont want it to idle at 1500! I forgot to add, the BLM is at 108, and the integrator is at 80, at idle! At 1500, the BLM is 114, and the integrator is 106.

I noticed Mike Davis has the exact same combo I have with LT4 HOT cam and L98 heads. But he didnt return my emails...

What can I do? Which values need changing in the chip so it'll think 11" of vacuum at idle is normal at 800 RPMs? Or is there a PROM already on diy-efi for this? Thank you!!

[This message has been edited by Kevin91Z (edited February 20, 2001).]

 

Kevin,

Dude - you have perfect timing. Read the post below entitled "P730: Part Throttle Fuel Tuning (No PE)". This explains exactly how to get your fuel curve right. I had the same problem when I installed my cam. Its easy to fix. Read that post and then reply to THAT post if you have ANY questions at all.

Tim

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TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

I saw that right after I made my post. Thanks Tim!

 

Mike is at least very slow with ansering emails, sometimes I waited over a month for a response.

Start with a known (stock) bin and build from there. Just little one step atta time changes. It's way overstated that having a similiar chip to start helps you. It's about learning, to get things right for your car. BTW, I've done two identicall engines, and to look at the chips you'd thought I was drunk thre were so many serious changes in them

 

I am starting with the stock 305 5-speed chip with WOT timing/fuel changes that I used with my ZZ4 cam and previous engine. I was hoping I'd get lucky with this LT4 cam and not have to make as many changes, but I wasnt as lucky.

Why do you think a PROM aleady setup for larger intake and runners, LT4 HOT cam, and L98 heads wouldnt work in my engine? The only difference is automatic vs 5-speed, which is easy to change.

 

Come on Kevin, get your feet wet and get REALLY into eprom burning!

If you had started it when you first made this post, you'd have your BIN right now and probably BETTER than anything that might have been sent to you.

There's a lot more activity on this board now, everyone is psyc'd, and the train is starting to leave the station. Don't miss the train!

 

Glenn, I'd love to get into PROM burning my own stuff, but right now I cant even drive the damn car. After I shut the car off, then restart it, it goes into limp home mode. The SES light is on solid, it idles at 1400 RPMs, and I get no data to my Diacom. The only solution is to unplug the ECM for a minute and try again. I just want to get my car driveable again, then I can get into working on the PROM. What's causing it to go into limp home mode upon restart?

 

At BLM/INT 108/80, you've hit the lowest limit you can before you throw an SES code 45 - O2 rich sensor. When you first start your car, you on in open loop but as soon as you go into closed loop, you will hit this code most likely and this is triggering the SES code adn the limp mode. The only solution is to reset the ECM.

First problem, is your 305 eprom. Forget it. You've been living on borrowed time and should have redone it a long time ago. Go get TunerCat and modify the displacement and injector pulse width and NEVER DISCUSS a 305 eprom in a 350 again.

Second, the overlap of the LT4 Hot Cam is like having a built in EGR at low rpms. You got to pull some fuel out in the lower kpas and also the lower RPM values to start. Think about the VE of an LT4 Hot Cam and translate that into the VE table. An LT4 Hot Cam is going to be less efficient at low rpms and low map, and more efficient and higher rpms. "ROUGH" out a VE table along those lines.

Next, bump up your desired idle speed a bit. This will give you a bit more vacuum. And try adjusting the IAC a bit.

All this is to get you to a "starting" point where the eprom will "run" well enough to not through the Code 45 and possibly a Low MAP code too.

This is a great lesson for others as to when NOT to get into eprom burning. The time to get into eprom burning is when you DON'T need an eprom IMO. That is when you can learn what all these tables do and not be faced with the daunting task of learning what to do to get a "starting" eprom while learning how to burn an eprom. Now you are faced with the situation of not knowing what to do, and having no "backup" eprom to work with.

But, try reducing the VE values a bit in the lower kpa values from 400 - 800 rpm area, raising your desired idle speed based on coolant temperature and twiddle with the IAC counts a bit. This is AFTER you adjust the 305 eprom for the proper displacement and injector flow constnat. Once you get the engine to "run" without throwing an SES code, then follow the new article on the P730 Intro.

If you don't have TunerCat, then buy it plus any of the other equipment.

 

Sorry for the typos and grammar errors, but it is very late and I just wanted to get you to a "starting" point. Remember, the above is not THE SOLUTION, just a starting point. You will have to figure out the solution on your own once you get the car running.

As I said, I hope others will learn from your error and not wait until they need an eprom to get into eprom burning. It is too late then. But hopefully, those suggestions will get you past the initial hump so you can at least operate without throwing an SES code and triggering limp mode.

Good luck.

 

Glenn, I forgot to say I'm not using my 305 chip anymore. I found Mike Davis' PROM on his website, and am using that. He has an LT4 HOT cam and L98 heads too. I wonder if it is something in the chip that messes up with my setup. It makes the car idle at 800 RPMs, and it runs a lot better than my chip, of course. I'm not getting any codes, and the INT is around 126-132 and the BLM is down to 108-112 or so. I'm not sure, I always get those mixed up. On the first start, it runs fine, the O2 sensor flips back and forth, the timing works, its just when I shut down, then restart it goes into limp home mode.

 

Possibly you should try erasing and reburning it again. I find that I have to progressivly increase my erase time after every so many reburns or it will trip a code.

Sounds to me that you are running a bit rich which you will have to adjust. Either increase the Injector Flow Constant or lower the VE values in the lower rpm/lower kpa region. Also, your injectors may be larger or you might have more fuel pressure.

You can adjust the idle and so much more in the eprom. Do you have TunerCat yet?

 

I've got this request for help on 3 different boards, I forget what I've said on each...

I'm running 22lb injectors, and the fuel pressure is now at 40lbs, with Mike's chip. We started at 48lbs but lowered it to 40lbs when it was very rich with the 305 chip.

I'm hoping to get with my PROM friend tonight and figure it out. If not, it'll be this weekend. :-/

 

Well I drove it home tonight. Turbo City modified a PROM for me enough to make the idle liveable, and got the BLM and INT close to 128. Now I just need to get my own stuff so I can narrow down the tuning. I priced some burners at Frys tonight. I'm going to reread Tim's tech article and then post what I found.