Back fire at start

[efnfast]

Just put headers and exhaust on the car. Now when I start the car in the morning, it backfires? kinda'. Injectors leaking fuel into cylinders? I've only had the car for a year and I don't know if they've ever been changed.
TIA Steve

:Eagle:

[VetteMed]

I was experiencing backfires on a consistent basis when I had a vacuum leak.

[efnfast]

It only does it when I first turn the key, before it really fires up. Seems to be running fine. Altough the idel has been high, and fluctuating. Maybe a vacuum leak, or just 'cause it's breathing better.

[-=Jeff=-]

leak in the exhaust at one of the pipe joints will do it too

[VetteMed]

High fluctuating idle is another common sign of vacuum leak. How is your cruise control and HVAC working (do all the different vent positions function properly)?

[efnfast]

haven't used the cruise lately. HVAC seems to be ok, but I'll pay closer attention. It does this before the engine even fires up. Like one of the cylinders had some fuel sitting in it.

[VetteMed]

yes, mine was doing the same thing when I had a vacuum leak at the junction of the check valve and the line that supplies the HVAC and cruise systems with their vacuum.

[efnfast]

Sounds like I better start looking for a vacuum leak. I would have thought a vacuum leak would only be a problem after the car was running.
Key on, engine not running- vacuum pump cycled at 1 min, 45 sec's. It only ran for about 2 seconds.

[scottfab]

I get a backfire every time I release the key too early after a start.
Solution: I keep the key turned a little longer.

[sammy]

might ck and see if the hose connected to the sensor at the back of the plenum is tight , it gets oil and heat soaked and can leak .

[RHanselman]

I bet you have a leaking injector... My 91 did this before I put RCs in it. I replaced the inj on my 90 with the 91 injectors and the 90 developed the same backfire at start up...

[Paul Workman]

I get a backfire every time I release the key too early after a start.
Solution: I keep the key turned a little longer.

Me too. A good practice especially since these motors normally roll over a tad n
longer before firing. An extra second on the start switch might save some plenum diving.

P.

[efnfast]

It's only been a couple of times, but I tried what Scottfab suggested, holding the key a little longer. So far so good. On the subject of injectors. From FIC. New or rebuilt?

[VetteMed]

I am running the rebuilts from FIC. They seem to work fine, but they are very sensitive to becoming stuck if they sit without fuel in them for any length of time. Jon at FIC has been great about servicing them as needed, but of course it's no fun to pull the plenum to pull the injectors after you just finished up another job. The price is right,though!

All things considered, I'd probably not buy the rebuilts again, but they are working fine for me as of now.

[GOLDCYLON]

I would not buy the rebuilds. Im running RC injectors a lot of folks have had notihing but postitive things to say about the Accels as well.

[John Boothby]

RC's. Expensive, but-----

Mine are over 7 years and 10K without a burp!

[GOLDCYLON]

RC's. Expensive, but-----

Mine are over 7 years and 10K without a burp!


5 years 60K no issues.

[efnfast]

Any reason to use anything other than the factory recommended unit? Bigger injector = more power?

[GOLDCYLON]

Any reason to use anything other than the factory recommended unit? Bigger injector = more power?


The Factory unit could not handle modern day fuels with all the EPA additives. They we actually melting the insides of the injectors and causing other issues like rust formation etc.

Back in the late 90s original ZR-1 owners were complaining to GM about defective injectors however GM would never acknowledge a defect with the comments of they were designed to perform before all the new EPA additive requirements.

So basically suck it was GMs response. RCs and Accels other than being new have a stainless steel sleeve that solved the melting and rust issue. These rebuilds do as well but Ive heard more than a few folks complaining about issue with the rebuilt injector having to be replaced or cleaned.

However I have heard nothing but great comments about the customer service of the rebuilder however that can only go so far when you have to keep pulling the plenum.

[efnfast]

Thanks GC, you missed my point. Not GM injectors, but the actual size and rating of the injector. Like diferent size jets in a carb. Can I put in an injector that will flow more fuel and give me a bazillion more hp?

[1990 quasar blue]

Unless they have changed the accells are 21 lbs. I believe factory are 22.8 lbs. Something you should tell Marc when you order the chip, if accells are what you decide on. Another thought regarding Marc and your chip. Does NH only have 10% ethanol like we do here in ma?

[GOLDCYLON]

Thanks GC, you missed my point. Not GM injectors, but the actual size and rating of the injector. Like diferent size jets in a carb. Can I put in an injector that will flow more fuel and give me a bazillion more hp?


Only if you add a Turbo type R sticker to your rear window.;)


The real answer is no unless you have had porting and headwork you need more fuel delivery in those situations because the flow has improved and changed. Simply adding larger fuel injectors wont do the trick.

[efnfast]

GC, already put the type R sticker in the rear window, didn't add nearly the hp they advertised. Nothing ever does.
1990 QB 10% ethanol for now.
So it sound like, unless my hand is forced, I'll wait until the car goes to Marc for porting to do the injectors, then Marc can pick them, seems he kinda knows what he's doing.

[GOLDCYLON]

So it sound like, unless my hand is forced, I'll wait until the car goes to Marc for porting to do the injectors, then Marc can pick them, seems he kinda knows what he's doing.


Concur

[scottfab]

Thanks GC, you missed my point. Not GM injectors, but the actual size and rating of the injector. Like diferent size jets in a carb. Can I put in an injector that will flow more fuel and give me a bazillion more hp?

This has already been answered but I'll add that if you ask the RC folks they will confirm unless you're upward of 500hp already then the flow will not benefit from higher flow injectors. I replaced all 16 of them 12 yrs ago and have had no problems with them since.
=D>

[XfireZ51]

Unless they have changed the accells are 21 lbs. I believe factory are 22.8 lbs. Something you should tell Marc when you order the chip, if accells are what you decide on. Another thought regarding Marc and your chip. Does NH only have 10% ethanol like we do here in ma?

The difference in fuel flow is actually non-existent. The Accels are rated at 20#/hr w 39psi FP. At the more typical 48-50psi in our Z's they flow ~23#/hour. So no calibration change is necessary.

[Paul Workman]

Thanks GC, you missed my point. Not GM injectors, but the actual size and rating of the injector. Like diferent size jets in a carb. Can I put in an injector that will flow more fuel and give me a bazillion more hp?

Negative. The proper AF ratio is what will give you the best performance; somewhere around 12.8 to 13.0:1 reading on a wideband sensor while tuning. Bigger injectors in closed loop will require less dwell time to satisfy the pre-determined AF ratio. As injectors get bigger, the dwell time gets shorter (in closed loop, i.e., idle) until the dwell time gets so short that the injector doesn't function well anymore and idle quality goes to hell.

Dom's right. On the WOT side, the stock 22# (or the 21# Accels) are more than adequit. Best power is made when the AFR is usually around 12.6 to 13.0 (varies with motor and atmospheric conditions at the time of testing), and there's plenty of dwell time left, even on a 500+ hp LT5. (Besides...IF it were that easy, we ALL would have spent a couple hours to swap injectors to some mega flowing injectors by now, instead of doing all that porting etc, etc. Just a thought.)

Just another thought... Take it from one who had a single injector go bad, you can end up burning a valve on that cylinder, especially if you're running with the secondaries intact. (another reason to chunk the secondaries, IMO). So, at least do a (hot motor) injector resistance test - all should be about 12-12.5 ohms for stock injectors. At 10 ohms, you have trouble on the way, and at 7 ohms...your idle may be the least of your worries!! Do whatcha want. I'm just sayin the 90-92 stock injectors can result in more than "minor" issues with idle/performance.

P.

[efnfast]

Marc is going to have a chip for me at BG. He's going to calibrate for 12.8:1 AFR.
I asked about a custom tune, he said not at BG, too busy.
I'm going to send a letter to the p.o. and see if he'll share any info. He may have already done injectors.
So if I change injectors now, I'm still covered when I get to the 500 hp range?

[RHanselman]

Marc is going to have a chip for me at BG. He's going to calibrate for 12.8:1 AFR.
I asked about a custom tune, he said not at BG, too busy.
I'm going to send a letter to the p.o. and see if he'll share any info. He may have already done injectors.
So if I change injectors now, I'm still covered when I get to the 500 hp range?

He tuned mine in 3 pulls @ BG several years ago and did a great job! I even got 4 more MPG on the way back to Vegas. 28 vs 24...