Gramsroc

1989 Iroc Z, 305 cu in, TPI, 15,000 miles. Runs fine when it is cold, but if the ambient temperature is warm, the engine misses badly when it gets to its operating temperature - acts like it is flooding. If the ambient temperature is cold (dec in N.E.) engine runs fine at the operating temperature. No codes or SES light. Good spark while it is running poorly. Good ohm readings from Intake manifold temperature sensor and coolant temperature sensor - both tested across full temperature ranges. This was in for service already for this problem, the tests were inconclusive, but it was recommended to replace all 8 injectors - the theory is all 8 failed. What is the possibility of this? The probability??? Any thoughts / assistance would be greatly appreciated!!

southbay08

how did they test them? What is inconclusive? What made them decide that all 8 injectors are bad? Did they give you any info?
Why don't you begin by testing the ohm on each injector. Readings should not be less than 11-12. Want to check for leaks...pull the plugs, if you have a wet cylinder then you have a leaky injector. You can also check to see if they are all pulsing.
Keep us posted.

p8dnful

I have a complete similar problem as to you.... At start up it idles great, as soon as it warms up, it idles rough.

At a normal take off from a stop light, it hesitates and feels like it has a major miss. As soon as I get up to desired speed you it runs decent to where you couldn't even tell if something was wrong with the car. On the freeway and at higher speeds there nothing with the car at all.

Another problem is when idleing for too long or after being driven for over 20 minutes or so there's a strong fuel smell but there's no leaks anywhere.

Within the past 2 months I have changed External Coil, Ignition Module, Cap & Rotor, Knock Sensor, Fuel Filter, Spark Plugs, MAP Sensor, Oil Change, Radiator Flush, EGR Valve, Fuel Pressure Regulator, Oxygen Sensor, Engine Coolant Temperature Sensor, Air Intake Temperature Sensor, and Fuel Injectors (Bosch III's). All parts replaced where OE replacement AC Delco from the Dealership.

Man I'm so Lost right now and so close to being broke

bigwilly262

I'm having the exact same problem with my 87 IROC 350 TPI. Runs great when the car is cold, plenty of power and no missing. But when sitting at a light in 90 degree weather and the water temp gets up to 220, the car misses terribly and wont accelerate and knocks if you give it too much throttle while its missing.

But if you can manage it up to speed it runs alright, which sometimes you can do by nursing it up in a low gear.

I just changed the TPS and cleaned out the throttle body w/ carb cleaner.

I just got it linked in to tunerpro but I'm really new at that and don't know what the ranges should be on all the sensor readings.

I'll keep searching the forums but I hope someone comes along that has had this problem and fixed it

NY87Iroc

iTrader: (1)

Any answers yet to this problem??

bigwilly262

Well mine has started missing randomly at any time not just when its up to temp. When it misses the 02 readings go to 4.44 mv, indicating lean and stay there the whole time its messing up. Also when its missing my fuel pressure oscillates between 0 and 50 psi really fast like engine speed fast. So it looks like my problem is somewhere in the fuel system pump-regulator-injectors. Not sure where though..

bigwilly262

My problem turned out to a bad pressure gauge and a bad fuel pump. My old pump could only pump it up into the 20s. Changed the pump and it runs great. Something to check out

87350IROC

iTrader: (2)

Check fuel pressure.

Could also be a Ignition Control Module and/or Pickup coil

fetthouse

Most likely bad injectors, the GM original injectors are noted for this. My 89 5.7 TPI with 27,000 miles did the same thing and then it eventually became very difficult to hot start. I replaced mine with some from Five-O Motorsports (Denso C302) that they said would be fine for my car. No more problem when hot but now it doesn't start well. It stalls repeatedly and runs rough in open loop. It runs fine when it goes into closed loop. I think these injectors were too small for my car (19# instead of 22#). Five O said my car would adjust but it didn't. I even put on an adjustable fuel pressure regulator but that did not help either. So I will again replace the injectors in the spring with some 22# units. I may try the Sorensen replacemnets.

southbay08

a 5.7l engine is not going to adjust to 19lb injectors. 22lb injectors are stock replacement.
Why don't you test the resistance on the injectors both hot and cold?
The stock multecs are prone to coil failure, especially when they are hot.

Black88Z

Does a 350 TPI use the same injectors as a 305 TPI?

I have the same exact problems and suspect F.I (no chance to ohm them out yet) but i need to know if a 305's F.i's will work on my 350.

Thanks

southbay08

No, the stock replacement for a 305 is 19lb, replacement for a 350 is
22lb.

Black88Z

Alright, gotcha. Thanks.

Black88Z

Where this says 29lbs per hr, does that mean its good for up to that much pressure? Would this injector work on my 350TPI?

http://shop.advanceautoparts.com/web...___#fragment-2

southbay08

No, first of all that injector is a little over one inch long. It would NEVER fit your application, it's a "pico" (small) injector! As far as the 29lb, that is not the rail pressure, it is the amount of fuel that will flow from that injector under a set pressure at the rail. For the 350 tpi you need a 22lb injector, we like the bosch lll's,,,,,they never let us down