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Discussion Starter #1
Hi guys,

I just had a new engine built for my '97 CVPI. It has coated 10.4:1 forged Probe pistons, Eagle rods, and "GT" cams which spec at 188/198 duration, .510/.540" lift. The heads are nasty stockers, with a valve job and those new 87 lb springs with titanium retainers.

The machinist installed the engine. It seems to run fine at higher RPM, but as at drops down to idle, it doesn't want to stay lit. It has very low vacuum at an idle, but I don't suspect a vacuum leak. The fuel and spark worked flawlessly before the new engine, I have no reason to suspect them now. The computer does give lean codes, however.

We pulled the timing cover off and checked the cam timing using a degree wheel and dial indicator. It seems to be correct.

Is this simply a case of the brain needing to learn to give the engine more fuel at low RPM? I thought being a MAF system, the fuel would still be correct, despite the relatively small changes to the engines tune. We didn't actually drive the car on the road, just ran it in the shop. It seemed to idle so poorly we thought something was wrong. Now, I'm wondering if it's just the idle fuel mixture being incorrect for the new engine...

Has anyone installed a slighlty modified engine before? Does the brain need to be re-programmed? Will it "learn" on its own?

Thanks,
 

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You have completely changed the engine dynamics over your '97 engine. Until you get the EEC calibrated or a chip, you are just going to fight it. You need a chip that at the very least looks like something that came with that motor. Compression being high will not be very forgiving too with the incorrect calibration. Do not assume your engine is slightly modded. You have made major changes compared to a '97 CV motor from what I know about them.
9.0:1 compression. Non PI heads and cams. Lower flowing ports.
The only thing that might limp it around would be to put bigger injectors in it to richen it up. But that is a shot in the dark too. The EEC may try to learn but probably will be at its limit for adapting.
 

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What it your FP?

Lifespeed,

What is your fuel pressure at idle with and without the vaccum line hooked up to the regulator?

You are either rich or lean and since you have DTC's showing a lean condition, you have to get it tuned. What fuel injectors are you using?

A-Train
 

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Discussion Starter #4
Re: What it your FP?

A-Train said:
What is your fuel pressure at idle with and without the vaccum line hooked up to the regulator? You are either rich or lean and since you have DTC's showing a lean condition, you have to get it tuned. What fuel injectors are you using?
I haven't checked the fuel pressure yet, although I can check it tonight. I'm assuming there isn't a fuel pressure problem, as the engine ran fine before it was rebuilt.

The injectors are factory. I didn't think the mods I made were enough to require that much more fuel flow. I would think a wider pulse width would be enough to give it more fuel, but I don't know if the computer will learn to make that adjustment on its own.

I spoke with D. Reinhart about tuning, and he said I had to take it to a dyno shop and get a map of A/F ratio versus RPM before he could make any attempt at tuning it. I suppose that is the most-correct way to do it.
 

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You'll run lean

If you added PI heads and or cams.
The heads will flow more air than the injection system can support with stock electronics.
Yes the MAF system is "flexable" but adding an increase in CR plus better cams(more lift more duration if I remember right). you've about maxed it out.
A swap to a bigger MAF with 24# injectors and a custom chip should do it.
I'm about to find out on my 95 XR-7 once I get the old engine out (10:1 Probe forged pistons, and 99 GT Cams in Stage 3 Ported 98 GT Heads-yes the cams do fit and work fine I drove the car for a year before I found out it had GT cams in it.)
PS you said "stock" rockers is there somewhere that makes aftermarket ones???
 
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