Does anyone know why my car (89 IROC-z 5.7 TPI) would suddenly start to run poorly in open loop? When I first start it in the morning it idles very rough and I have to tap the accelerator to keep it from stalling, and it hesitates very badly when I give it a little more gas. Once it warms up and enters closed loop it runs much better.

I've replaced the plugs, wires, cap, and rotor. I've also replaced the coolant temp sensor - all to no avail. I've checked the fuel pressure which is strong and the TPS voltage is normal.

Any suggestions would be greatly appreciated.

 

Sounds like a CSI problem to me. Check the 9th injector for frayed wires or see if it's unplugged. It's on the drivers side of the intake manifold, in between the two pairs of runners. hth

 

My car doesn't have a cold start injector. They stopped using them after the 88 model year and my car is an 89.

 

i have the same problem with m y 89 and i ahve changed everything to no avail

i really dont know what the problem is

 

I've lived in this world for about 3 years now. Does your car run rich too?

 

it seems to be a big problem

wonder if it is ecm related??

 

how many miles are on the engine? how long has the car been running poorly in open loop?

did you test the CTS before you replaced it? you can look at it's voltage and compare it to a chart of GM dual range CTS voltages and their coresponding temps. when the car sits overnight the engine coolant is pretty close to the ambient temp that morning. lets say it's 65 degrees out side, Key on Engine OFF (KOEO) you test the CTS voltage and you should get about 2.56 volts. if you get something like 3.8 or 4.7 volts the CTS is telling the ECM the coolant is like 30-18 degrees and it will run like crap.

this is caused by high resistance somewhere in the circuit or at the connector it's self, causing the CTS to lie to the ECM. most of the time GM gives you a new connector with the CTS. maybe some wires moved and caused a problem.

also remember TPI is a batch fire or gang injection system, it fires each entire bank left or right at the same time. this makes for a lot of carbon build up on the intake valves of a high mileage TPI engine.

The carbon soaks up the fuel like a sponge, causing poor running when cold and hesitations. after it warms up a bit and the carbon has soaked up enough fuel to begin to let it run off and not soak fuel you've just about reached closed loop and now the 02 sensor is giving input to sense, compare and correct your ST fuel trim and the car probably runs O.K> possibly try some EFI system cleaner, only do it once though, if it does not help don't do it again.

sorry for the lengthy response. hope those suggestions help.

 

where is that chart?

 

i'll send you one, if you want.

 

ya send it to my email

jerflash@opronline.net

thanks alot

 

sent. the left side of the dual range section is the cold side, that is what you want to compare you readings to. good luck.

Mike

 

im so stupid is jerflash@optonline.net

not opr

sorry can you re send?

 

hope fully that went through. let me know if it did not.

 

Hey, I want you to try something for me. Take a paper clip, or something similar and jump the diagnostic connector from A to B (same pins as if you've ever tried to pull codes with the engine off) Do this when the engine is cold. Start the engine, and the Check engine light should be blinking rapidly (twice per second). Drive the car around, and when you see the check engine light start to blink more slowly (once per second), you are now in Closed loop. If when that happens, you notice the car driving differently, then you know it is specific to the car being in open or closed loop. If you notice a gradual change in performance, either before or after it enters closed loop, then you know it may not be specific to that, but could be related to something like the ECT like what mike mentioned. Let me know what that does.

 

If you notice a gradual change in performance, either before or after it enters closed loop, then you know it may not be specific to that, but could be related to something like the ECT like what mike mentioned.

Cool test!

 

My 88 is doing the same thing. As you have done, complete tune up, even new injectors, still rough for a few seconds on cold start and takes a while to fire at that. I've noticed some oil smoke on startup for a while now and I'm assuming the valve seals are going so the buildup on the back of the intake valves is a real possiblity. Think this might be a winter project to pull heads and rework them. Be a kick in the a$$ if that didn't fix it though.

Good reading here:
http://www.swri.edu/3pubs/brochure/d08/qualify/qual.htm

 

well i have replied to all of these posts lately, there are many many of us that have the same problem and no one knows what the deal is, i am tempted to e-mail some of the guys on the DIY-PROM board and get them in here to help us figure this out.

all the suggestions above are possibilites but i can tell you that i have replaced all of the above and my car still does it. it did it stock, it did it after the rebuild, and it doesn it now with my aluminum heads. i have also replaced the CTS, i replaced the MAF last summer becuase it went bad, i have tried everything and i cant figure it out. the next thing for me to do will be to get a laptop and the correct software and start datalogging this thing when it acts up on cold starts and see what hte heck is goin on. my car starts right away but instantly wants to die, and runs really really lean, it pops through the intake and hesitates really bad. yes i have checked my TPS and my ignition timing too. so if anyone had any NEW suggestions i am open to hear them.

 

send me a detailed description of the problem, when it occurs and how frequently it occurs. also the year of the car, milage, ALL mods that have been done, and every part that has been replaced. i will take that info to my advanced engine performance instructor Mr. Morton, he is one of the best trouble shooters on the east coast, he wrote the ASE L-1 advanced engine performace test.

we'll take a shot at it and see if we can't crack this bastard.

wtrapp@comcast.net

 

by the way nice suggestion for isolating the problem dan.

 

FYI, my 89 Formula 350 (L98 700R4) had a cold start injector. That engine is now in my wife's 260Z. It may be worth your time to check and see if you have a CSI or not. I am by no means trying to be an *******, but the break seems to actually be in 90, not 89 as I was lead to believe. Basically, if your car has a MAF, you've got the 9th injector. That damned thing crapped out on me and I banged my head against the wall for months, until I noticed it was not plugged in (the plug broke and fell off), a new plug and all is well.