89 Firebird Formula - Idle hunts, No power

Hey guys, long time A/F-er, first time F-Body posting. Some background on this Firebird situation: It's an '89 Firebird Formula 350 TPI automatic w/72k. I got it after the guy said it died and would no longer start. After a change of the horribly fouled plugs (all fouled evenly by the way) it fired right up, but ran real rough, had a shaky idle of about 350 RPM, and was running so rich it looked like logs of soot coming out of the tailpipes, not to mention it had no power at all,and a massive hesitation. Every so often I had to rev it up pretty good to keep the plugs from fouling up entirely again. He had just replaced the MAF sensor. I replaced the O2 sensor. Eventually a had it scanned (It's got the OBD-1 that cannot be jumped). The shop said the ECU was shot. SO, I replaced it. Advance Auto had one right in stock.

Well, now to where I'm having issues.... It no longer runs rich and doesn't wanna stall out, which makes it more drivable. It's responsive as well. However it's still dogging, and anything past about 1/2 throttle and it just falls flat on it's face. It also hunts for an idle dipping down to 400 RPM and jumping up to 1500 RPM. TPS checks out, and as I said O2 and MAF are new as well as the ECU. I've checked for vacuum leaks, none. Checked for leaks in the intake duct-work, none. I checked the fuel pressure regulator with a hand vacuum pump, and it holds vacuum. Performed a fuel pressure check, and with drastic throttle changes, the pressure ranges anywhere from 39 psi at idle to 45 psi at high engine speeds. Any advice? I'm normally fairly good with diagnostics, but I'm stumped :banghead:. Granted this is my first TPI verses TBI and E4ME Carb which I know like the back of my hand, but it really doesn't seem all that different. Thanks in advance for anyone's help!

hmmm,

What's the TPS set at at idle?

Have you ran all the old fuel out of it yet?

And you should be able to jump the ALDL.

I didn't know you could set the TPS on this. Yes all the old fuel has been run out. Jumping the A and B terminals resulted in no response, however that could have been because the ECU was toast. I'll try it again with the new one to see if it throws it into diagnostic mode, however the check engine light hasn't come on since the computer replacement.

Yeah, the applying a jumper to the terminals yielding no results is a little concerning.

Setting the TPS is standard procedure by backprobing the reference and ground wire, if memory serves they are the two outer wires? Procedure is done key on, engine off. Closed throttle the sweet spot is in the neighborhood .52V.

Alright, something I can work with. I'll try it out tomorrow after work, and I'll post back. Thanks!

Took longer than I hoped to get to it. It looks like she's sittin at .515 volts at idle.

Kay, that's good. Have you tried cleaning and resetting the IAC? Also I'd try disconnecting the battery and resetting the ECM.

Kay, that's good. Have you tried cleaning and resetting the IAC? Also I'd try disconnecting the battery and resetting the ECM.

I have tried resetting the ECM with the same result. I haven't done anything with the idle air controller, I'll try taking it out and try cleaning it up with some carb & throttle body cleaner. Is there any way of testing it like I did with the TPS? Also would the IAC affect the car's current overall performance, or lack of I should say?

Okay update... As you may have gathered based on length of time between my posts, time is something that's hard to come by for me. Regardless, I cleaned the IAC which resulted in no change. I ran a seafoam treatment directly into the intake figuring when it ran so horribly rich it may have built up a lot of carbon. That actually helped. The car's got more pep, and response. It still dogs a little though, and still hunts for an idle. a mechanic said to ohm test each injector to see if I've got on that's going. Do you know what resistance I'm looking for in a good injector?

I want to say around 16 ohms off the top of my head?

Okay, I may have found the problem. Here's the result of the injector test. On cylinders 1,3,5,7 I got 15.6, 15.5, 12.4, 12.2 ohms. On cylinders 2,4,6,8 I got 12.5, 8.7, 13.1, 16.1 ohms. I know they're accurate readings because I did it twice and got the same result. I did it almost five times on cylinder 4 :rofl:. It looks like injector 4 definatly needs to be changed, but realistically I should just replace them all huh? I was exploring purchasing them over the internet because even with my employee dicount at Advance Auto Parts I'm still looking at $50 each. Here's where I let loose the flood of questions: I see different pound ratings for injector sets, what does that actually mean? (PSI handling? Output PSI :confused: ) What is the factory injector pound rating and should I stick with that or go a step up? Is it true that Ford TPI and GM TPI systems use the same injectors? Anything else I should know about choosing replacement fuel injectors? Like I said earlier, I know TBI like the back of my hand, I'd prefer not to learn about TPI the hard way :grinno:. Oh and thanks a ton for the help so far!

If memory serves, and it's not so good these days BUT I was right on the ohms, sooo...... I think the stock injectors are 19-22psi. Oddly enough, the Ford injectors are plug and play and are the better option.

i think you should change the coolant temperature sensor for the ecm.

Good point, it's cheap, easy to do, and more detrimental to fuel trim than the o2. None the less, the injectors are half caput.

agreed on the injectors needing replaced, but since he didn't describe a misfire situation makes me think the CTS is the main culprit

Injectors are def a big part of your problem, But i would have to agree with geno on the CTS sensor, I chased a similar problem in my 355 last year, checked injectors, changed intake gaskets, turned out to be a faulty CTS. BTW i have a complete set of Accel silver bodied 24lb fuel injectors if you interested in il cut you a deal on them as i need 30's or 36's this year.

Injectors are def a big part of your problem, But i would have to agree with geno on the CTS sensor, I chased a similar problem in my 355 last year, checked injectors, changed intake gaskets, turned out to be a faulty CTS. BTW i have a complete set of Accel silver bodied 24lb fuel injectors if you interested in il cut you a deal on them as i need 30's or 36's this year.