tchernobog

Currently driving a '91 z/28 305 TPI.

My gas mileage is absolutely horrendous. I mean...really, really bad.

I did some figuring, and I'm getting between 6 and 7 mpg, which is nowhere near what I should be.

I do not rag on my car, I baby it, I rarely break 2500 RPM's, (none of this ) so there's gotta be a reason my mileage is so horrible. Running stock gearing, proper tire inflation, etc.

My guess is EGR, but I'm not sure. I have a fresh TPS and IAC. EGR is pretty much the only thing I can think of that it could be, but, I'm sure there are people a lot more knowledgeable on here that could offer some insight.

KNBlazer

does your car stumble sometimes? that could be your EGR... how old is your O2 sensor? how about your CAT? you will have to do some basic troubleshooting on the EGR, to either confirm or rule out the EGR as the Culprit of your poor fuel economy...

tchernobog

It does, occasionally, though I wouldn't say often.

O2 sensor has about 15k miles on it, cat has about the same.

How do I go about troubleshooting the EGR?

Searching hasn't brought up much for me, sadly.

KNBlazer

it's been such a long time since I diagnosed an EGR...

tchernobog

I've never actually diagnosed one, only replaced.

I'm hoping I can diagnose it while it's on the car, because I'd rather not have to remove the plenum

KNBlazer

I believe you have to apply vacuum to the EGR if it stumbles and dies, it's working if it doesn't then your EGR is bad.. but to be honest I don't remember... try googling EGR DIAGNOSING OR DIAGNOSTIC...

87IROC-DAN61

Hello tchernobog!!

If the EGR wasn't working, it should throw a code 32!!

Have you checked out your fuel injectors!!!

They could be dripping the fuel instead of spraying the fuel!!

Does your car run rich???

Lots of black smoke???

Get your injectors cleaned first, you'd be amazed at the difference!!!!

tchernobog

I personally checked each injector, each one was either cleaned/rebuilt or replaced. Fuel pressure is between 39-42. A little low, but not terrible.

I may re-check them. Car runs a little rich, not too bad though. The idle is a little higher than it should be, which I'm thinking is obviously related haha.

Went out just now and checked what I could on my EGR. Vacuum line had come out of its little boot

I get a code 32 very infrequently, never in city driving, only after 1+ hours of highway driving, and even then, it's very infrequent, which is why my guess is the EGR.

I guess I'll have to check my EGR for vacuum tomorrow, sigh.

KNBlazer

You still have the hard plastic lines? I replaced all of mine with regular hoses... they crack real easily... at least IMO...

tchernobog

They do crack easily. It was a horribly stupid choice on GM's part.

My car is entirely stock, it's only had one owner, he bought it when he was 55 in late '90 haha.

87IROC-DAN61

Hello tchernobog!!

I get that code 32 also, happened right after I replaced my exhaust system!!!

The EGR passages might need cleaning up, also once you get the gas mileage back, and the car is not running rich, make sure you replace the O2 sensor, and be careful that your "cat" isn't burned up due to running rich!!!

Apply some vaccum to the EGR valve, and see if it moves the diaphram, and holds the vaccum!!

tchernobog

Well, I replaced the stupid plastic vacuum lines with actual hoses, then checked the EGR, it's working properly.

Unfortunately...since I've replaced the vacuum lines, the car now hesitates on light throttle, and has a very slight surge while cruising.

redfox

would the pcv valve have any thing to do with it? just wondering

86NiteRider

iTrader: (10)

Get rid of the CAT. You will be amazed at the difference in your car.

Chevy86 IROC-Z

iTrader: (17)

I would check with your DMV to see if you would require a smog test every so often. If not, then cut it and hold onto it, you may need it some time down the road. Nice Camaro 86NiteRider, although the NiteRider sounds a bit 1982 Pontiac Firebird.

87IROC-DAN61

Hello KNBlazer!!

I think that they are actually nylon...........I could be wrong, but that's what they look, and feel like!!!

Nylon = Plastic?????

87IROC-DAN61

Hello tchernobog!!

EGR/IAC, check to see if both are operating up to snuff!!

tchernobog

Well...hot-tanked my entire intake, (upper/lower) cleaned the injectors and EGR, I'm now averaging 14 city, which is not bad at all for a 20 year old v8

KNBlazer

how is y our F/A ratio? did you replace the O2 sensor?...

Chevy86 IROC-Z

iTrader: (17)

Very nice. I get around 13-15 highway/city. To get to work I gotta drive down the highway, then drive a few miles in town to get to work, along with an occasional code 51. I think I need a new or reman ECM.

Mr Froman

You can replace the plastic lines...?

faisal

Any could verify if there is no difficulty in press back the fuel rail in install progress after cleaning injectors , saw this video and that squeeze object I don't have

would I face the same issue ?

vinny R

Try using Rec 90 gas, non ethanol. There is a thread in TPI about this. It should not only improve your mileage but the car will run so much better. When these cars were made Ethanol in gas did not exist. The computer is tunned for pure gas.

Pro

Dont take it apart like that dumbass did
Do it more like this guy did
The 4 bolts on top and the 1 bolt in the front that holes the fuel lines in place.

faisal

OK any advise for injectors cleaning , or replace, I don't know what the factory injectors number is , I read 22LB and 19LB and I'm chasing good performance and fuel economy , some thinking of just clean them , is there any possible of bad performance as a result of cleaning ? Thank you.

1991 TPI Bird

Pro

You might could do like Iman does in this video

t/aws61985

iTrader: (2)

Get a new fuel filter. I was getting the same MPG as you in my 86 TPI when I was first getting into cars. The fuel filter was so old and clogged it weighed like 5 LBS. Like $10 fix.