I'm having an issue with my L98 TPI/SVO injectors. I'm dialing in the new rear-end and Stage III 700. Meanwhile, I noticed the idle starting to increase from around 600rpm up to 800ish rpm, and now increasing further. At the same time, the system is starting to dump more and more fuel into the cylinders, cutting power and causing the engine to 'rattle' under full throttle. Also, it's dumping fuel into the cylinders when I shut it off. SVO injectors are new and balanced. Complete ****-retentive tune-up has been done.

There are no engine trouble codes popping up, and I removed the 9th injector long time ago. Could the EGR be contributing to this issue or a single sensor be involved????

I was just going to introduce an MSD box and coil, but don't want to hook it up till this issue is solved.

Solid, well thought out idea's anyone???? It would be appreciated; Nitro

 

Did this start after you put the SVO injectors on it? What size are the injectors? What is your fuel pressure? Do you have an adjustable fuel presure regulator? Did you replace the orings when you put on the new injectors?

 

Good Questions. I did the injectors last year, about 1500 miles ago. At that time I did the full tune up, new injector seals, added the AFPR which is set to approx 46ish psi. I believe it was the larger SVO 24# ers. It's always run a little rich and I've been rebuilding so much of the rest of the car that I havn't had time to return to the TPI. I had adjusted the TPS and checked the output of the distributer electronix.

So I'm wondering if it could be a combo of the EGR interacting with the IAC???? I havn't had a problem since I did all the tuning and updating a year ago, until I started dialing in the new rear end and tranny. That's when I noticed my idle was starting to increase. Then recently, but idle and fuel dumping both jumped quite a bit. Nitro

 

What is your theory on the EGR and IAC interacting? Does your new trans have any vac. lines that could be sucking trans fluid into the intake manifold? My experience has been that if I have a problem with something after I made a change the cause of the problem is related to the change I made and not some other parts that just happen to go bad. thats why I think it might be related to the new trans you put in.

 

My question is why would you run larger injectors if you have done any mods to the engine?? It would have been more ideal to run the stock injectors with an adjustable pressure regulator and just run the pressure a few psi above normal to get better atomization of the fuel. The old philosophy applies here if isn't not broke don't fix it...

 

New tranny = tighter parts = higher load (LV8) = more rich (on top of bigger injector) = more IAC air = higher Idle.

check your blm's at idle might be at limit of ecm.

Get APR and lower fuel pressure SVO's are made to run from 20 psi to 60 psi per fac spec sheet. thats a 22# to 29# injector

 

Now that's an interesting post. I'm going to hmmmmm it for a bit and get back to you about it.
I did pull my IAC, and found lots of heavy carbon build up. Since it was the original 150k miles unit I went ahead and just installed a new one. I havn't had time to check yet for anything else or verify any difference. The new tranny IS the newest item, along with the totally tightened up suspension.

I also need to point out that I had PCM'sforLess set up my initial PROM so I could quickly ditch the cold start injector and allow for the SVO injectors. The reason for the better injectors was that the old ones were worn out, AND I was planning on completely porting my TPI system. Just mega porting the plenum added an extra 800 rpm into the powerband.

I'm just starting to understand PROM info, so will take some time to understand the point Pandin just made.... Thanks guys, Nitro

 

CEP89 ;
Why I was thinking that it might be a combo of both the EGR and the IAC, is that I've had a bit of a throttle tip in hesitation and signs of emmision issues that would cover the EGR, o2 sensor, or catalytic converter. Three years ago, the prior owner had a smog issue and he replaced the entire exhaust system with full 3 inch piping including the cat and also replaced the o2 sensor. When I purchased the IROC from him, the L98 was showing it's age, but it still passed California smog with flying colors.

This is my very first time at attempting to diagnose and understand how an TPI EFI system interacts with all of it's sensors. I've been so busy taking care of upgrading and replacing the entire suspension, trans, rear-end, little electrical glitches, etc, that I'm way behind taking the time to open up a computer and study PROM's as of yet.

The IAC was suspect to me as the idle kept increasing after the final tranny redo as I was installing and testing all the myriad of new suspension parts. Sure enough, I just pulled it out and it was heavily caked with dry black flakes. The idle instantly smoothed out to about an even 850 rpm in Drive. It's still running high and rich, but not the huge amount it was initialing starting to spew out the tailpipe. Now I'll need to research Pandin's info so I can understand in layman's terms what's the details behind his observations.
I have an MSD ignition set-up that's ready to install, but don't want to do it till I've got this issue figured out first in case it acts like a bandaid. I also had a friend help me reinstall the plenum when I first took it apart to clean it all and ad the AFPR. I'm wondering if I just might have an internal vaccuum leak due to a TPI gasket being installed backwards. Is that possible???

My heavily ported and siamesed SLP runners and Edelbrock base are with the gentleman who's building my new sibling ZZ4.5 engine. If he's going to take much more time, I may just go grab those parts and reinstall the entire TPI with loads of sealant and thermal barrier coatings....

What's your thoughts currently? Do you think I'm missing anything else??? If I understand it right, if the o2 sensor is failing, it shouldn't cause the extreme amount of dumped fuel I've been hit with...?????? Nitro-Nicky

 

One of the things they do to a built 700R4 is increase the mininum pump pressure. It is what makes that low throttle shift so nice and crisp. When you go from park to drive does it want to go. As to have to hold foot on brake to keep it from leaving.

The computer see's this as more load. A higher load will increase the pulse width. A computer run engine will tend to idle higher when rich because the IAC opens to compensate.

That is different than a manual carb. Back when cc carbs came out more than one guy has twisted off the throttle shaft. They were trying to lower the Idle by using plyers on the butterflies and manually adjusting the arm. When restarting the computer would just move the arm farther open. Do this 3x = one Junk $400.00 carb.

In your case using a scanner to look at what your engine is doing, would go a long way to help sort this out.

BTW what is your fuel pressure set to? And have you readjusted the maf. Both of these will affect that richness issue.

Since you do not have the cold start you are likely to have the 89 $6E bin installed, as modified by the chip programer.

 

Good/Great Afternoon to You, Pandin!

Yes!! One of the frustrating reasons I had to return to the trans shop that built my Stage 3 700R4 is that I'd shift it into gear and the engine would rev and SLAM into gear! I am assuming this is what helped/contributed to the destruction of my new set of posi cones. Initially I was fascinated; as it was almost like the new tranny could read my mind just by getting my hand near the shifter. Of coarse I had them correct this mistake and put myself through a quick coarse in 700r4 rebuilding to understand what was used proffesionally in the different 'stages' of improvements. That ended up being a good thing as I figured out they had made a couple shortcuts in the initial build and could now document it (so when my one year warrenty expires I'll have leverage). Now it shifts smooth but firmly into gear and the idle did drop a chunk- it had climbed from the 640ish rpm up to 1200-1400 rpm initially and the raw fuel smell had dramatically increased.

No, I have not played with the MAF yet. I'm planning on making a 3.5 inch MAF once I increase the size of the filter housing and learn how to program or at least read. The factory injectors were pulsing at a low 38psi, so when I installed the new SVO's and hogged out plenum, I dialed them up to 48 with the vaccum disconected.

I am in the process of choosing the equipment I'll need for scanning. Some people are using a Sears OBD 1 unit, others a computer and CD set, and I'm sure you're well aware of the various other items out there. My personal goal was to have the basics down by April 1st (i'm big on setting goals). As of today, I have NOT started, other than purchasing a few guide books to get the theory down.

I will absolutely hook up a scanner this week. Do you have a suggestion on what the minimum type of scanner I should look out for??? And have you found a really good publication and or info source that's designed for dummies???? I really do appreciate your input on this. It's the first time I havn't felt like I was chasing my own tail. Nitro-Nicky

 

I bought the hand held auto xray 3000 off Ebay $100, OBD 1 stuff sells cheap cause its out dated. I got a differant one at first for like $60 but it wasn't as good less outputs harder to use and read the screen.

one son has a 87 vette, the other 88 350 Iroc, daughter 86 vette. first scanner gets passed around a bit.

also with a laptop and cable you could use tuner pro or datamaster. There are like 25 outputs to read.

hand helds are small easy to use but only give limited viewing 5 outputs at a time and very limited storage.

laptops can scan for like an hour, so with a spread sheet you can look at it all and graph it if you want anything vs anything. even differant scans, cars.

Laps are harder to hook up and use in a moving car or for a quick check of say tps or idle speed.

you have just enrolled in a learning oppertunity very similar to going to college. You can just take a few classes or spend the money for the full PHD.

But you aint gona get all together in a day. Good luck.

HoJo

 

....I should recant on the MAF- Since I didn't get a printout of what the PROM builder did, although it made a wonderful difference in the car's overall idle, throttle step-in and consistancy.

I read through the Beginner's guide to PROM readin' & writtin' and it's definitely going to be a 'Road Less Traveled', bet definitly worthwhile!

Again; major thank-you's for pointing me in the right direction- Nitro-Nicky