Hey everybody,

I'm new to the boards here...just bought an '89 Formula 350 as a project car. It's my first third gen, but my second F-body. I'm the fourth owner of the car...it's got heaps of miles (224,450+), but is in overall good shape...the original L98 was rebuilt 20k ago and it's in immaculate condition. But there are some gremlins involved that I'm trying to work out, and I could use a bit of advice. I'm also new to wrenching, so a smidge of patience would be helpful too.

I'm attempting to solve my biggest problem first, and that is the subject of my fuel mixture. I suspect it is too rich. The car reeks of gasoline after being driven, particularly on the outside, around the rear. The exhaust smells sweet, but there is no smoke (except sometimes a little puff of black when the car first starts up cold) and I didn't see any deposits in the tips. Then there is the rapid fuel consumption. The car is chomping down a full tank of 93 octane in around (estimate) 125 miles city / 200 miles highway. I know these aren't economy cars by any stretch of the imagination, but it really seems to be gulping it.

And at revolutions below 2000, it drives all spotty, growling and surging, particularly around 1500 RPMs. Combined with the poorly-fitted exhaust pipes whanging against the rear valance as I drive around my neighborhood, everybody probably thinks I'm driving a POS. But seriously, when I open up the throttle, the car just goes and goes with no hesitation. It runs beautifully above 40 miles an hour!

Now, "factory spec" has not exactly been maintained on this car (meaning the engine has been upgraded by its previous owners) so I am not expecting factory fuel consumption rates, but I still feel something is wrong. The car does have brand new Bosch Platinum plugs and Accel 24 lb. injectors. However I believe the PROM is stock, as is the cam. The motor was bored .020 and ported/polished. It had a new fuel pump installed a couple months ago. Those injectors I mentioned were just put on about a week before I bought the car. Apparently one of the old injectors failed so the previous owner just bought a whole new set of 24-pounders. I believe those are safe to run with a stock PROM, but you wouldn't want to go any higher.

I have never seen the Service Engine light come on (except during the normal ignition test cycle) and no codes have been stored. The car is also not leaking any fluids that I can see. At this point, my first guess is going to be the O2 sensor, since according to the previous owner's documentation, it has not been replaced since the car was in his care. While I've got your attention, however, I wanted to know if there's anything else I should check or look for. I should also mention, since I don't know if it matters, that the original dual catalytic converters have been cut off and replaced with 3" straight pipe. I have not yet investigated what has happened to the AIR system.

As I said, this is my first third-gen and I'm incredibly excited about it. The car is a bit "middle of the road" in terms of condition; it's got some quirks, some gremlins, some leaky T-tops, and one really lousy paint job. But in the end it's gonna be beautiful, and it all starts right here. BTW, this board has already helped me solve a handful of smaller problems, via information learned just from reading the old threads. I don't know what I'd do without this community!

Thanks to all in advance.

 

i would start off with a new O2 and complete tune up (except plugs if they're new).

welcome to the boards

 

Thanks! That's a nice Formula 350 you have yourself.

Yeah, I hope it is the O2 sensor...that would be a nice simple fix, but such problems are not always nice and simple...

 

You know im having the exact same problem with my 92, except mine is a 3.1, I think ill try the O2 tommorow, is there any way to test it first?
Heck next important question where is it located?
thanks
Craig

 

If this car is a project car, then you will need some analysis tools, like a fuel pressure gauge and a data logger.

In solving any fuel problem, the first thing you check is the fuel pressure.

Also, a data logger that shows what is going on with the engine is extremely usefull.

I agree with the others, sometimes the O2 sensor goes bad, especially, if leaded fuel was used, or if it was cleaned (you never clean the tip on an O2 sensor).

 

Nobody else caught the fact that you are running 24 lb/hr injectors with a stock 22 lb/hr prom...you are running rich...that is why your mileage sucks...

You should get a new chip burnt for the correct lb/hr injectors...also, the longer you drive it like this, the better chance that you will kill the cat due to loading it up with unburnt fuel...

Also, since you have been running rich, the O2 sensor may be bad due to heavy deposits forming on it...I have seen it on other vehicles with rich fuel issues..

HTH,

 

Aha, so the 24 lb. injectors are at fault, eh? Now that you mention it, this seems very likely to me. The previous owner had just put these things in, and so the rich condition probably didn't exist beforehand -- that's why there's no sooty buildup in the tips; this hasn't been going on for long. I thought I had read somewhere that 24 lb. injectors were okay to use with the stock PROM but that they were pushing the limits of the chip. Guess not, or at least not in all cases.

How much does it cost to get a PROM custom burnt? I may be better off buying a set of 22 lb. injectors for the time being. I've got a lot of other stuff I need to do and I'd sooner return it to a more stock condition while I test some other things.

No need to worry about killing the cats though; the previous owner took 'em off.

Doc is right; I'm going to need some better tools and I am already planning on getting a variety of gauges, a multimeter and some other goodies...

Thanks!

 

Raw fuel smell around rear of car = either broken tank filler neck (very common, there's a recall on this, visit the dealer) or broken fuel line near the tank (also very common)

 

RB83L69, I would be inclined to agree, and I did think about that, but I believe the fuel smell is coming from the exhaust...

BTW, what flow rate do the STOCK 350 TPI injectors use? 21 lb/hr or 22 lb/hr? I've seen both said. Shopping around, I'm not having any trouble finding a 21 lb/hr set, but I'm not seeing a lot of 22 lb/hr sets out there.

Thanks!

 

Stock 305 TPI injectors were 19 lb/hr and stock L98 (350) ones were 22 lb/hr...

The Accel injectors are rated the same as GM rated them while the SVO injectors are rated slightly differently...ie, a 24 lb/hr SVO injector is more like a 26 lb/hr injector under the GM rating...

I would not replace the injectors, as they are new...but simply get a chip burnt for the correct injector constant...that way you have more room for upgrades later...

HTH,

 

I heard from the owner of fiveomotorsports (large injector retailer) that only 85-86 got the 19's while 87 - 92 had 21ibs injectors for 305's..

 

Thanks 88TPI406GTA. I would prefer to get a chip burnt as well, I was just wondering if it would be within my budget right now. Do you have any recommendations on where I could go to order a custom PROM? I don't think I'm at the stage where I could burn my own...yet...

 

Actually, maybe I COULD do my own PROM. I have a laptop already...guess I'll go check out the DIY PROM board and see what I can learn.

 

It really isn't that hard to do...and besides for less than the cost of a custom PROM from someone else, you could burn your own...

I have the Pocket Programmer II and like it...definitely check out the DIY PROM board for more info...

Good luck.

 

Thanks! Did some reading on the DIY PROM board and that great tech article out on the main site. It looks even easier than I thought. Was looking at getting the Pocket Programmer II and an adapter/ZIF/EEPROM starter package over at Craig Moates' site.

By the way, since the previous owner of my car experienced an injector failure a few weeks after installing the new fuel pump (which led to him installing these 24#s), does it seem likely that the fuel pressure could be too high? I'm thinking I'll go out and get a fuel press gauge and check it. One way or another, though, my computer definitely needs to be adjusted.