Ive been having all sorts of fun with my 1990 3.1 V6 swap. I swapped in the engine and ECM from a 1990 Lumina into my Fiero with a 5 speed. I had the chip tuned to compensate for the manual trans. For a few months, my car ran really rough and lopey.... turned out to be a stuck IAC. After the IAC was fixed, the car idled nice and smooth, but had a wandering idle. I found a used TPS and swapped it on, problem solved. Now my car idles smooth and where it is supposed to. The one problem I have now is that the car hesitates when you blip the throttle. If the car is sitting at idle, and I give it a quick, light tap of the throttle, the engine bogs down and then revs up. You can hear the engine suck for air, then rev up. It is really annoying at normal driving speeds when you go to shift gears. At WOT though, it has no problem. I found another used TPS, put it on and it didnt help the hesitation and the wandering idle came back. I went ahead and put on my good used TPS and tried swapping MAP sensors. With 3 or 4 different map sensors, it still has a hesitation. I got out the fuel pressure gauge, and with he key in the ON position and the engine off, I get 40 PSI. At idle I have 35 PSI and when you rev it up, it reaches 45 PSI. When the engine hesitates, the pressure increases. I stuck a new fuel filter on tonight, and it seems like the hesitation might be worse now. The old filter had a reddish brown colored gas come out the inlet when I took it off. The fuel pressure is still exactly the same with the new filter. Im clueless as to what to try next. I do have a scanner which allows me to see sensor information, and I cant find anything abnormal. Anyone have any ideas? Thanks!

I'm thinking dirty injectors. at first I was thinking fuel pressure, but you did check. and, it does sound like a fuel delivery issue. is this a 3.1 with Fiero intake, or a full Lumina alum head 3.1?

It is a full Lumina 3.1 with aluminum heads. I swapped it and the ECM in place of my iron duke and original ECM. Im going to do a few more tests today to try and figure out if the fuel pump is weak.

Well, I think I may have it narrowed down to a few things. I think that the TPS might be bad, causing the hesitation at light throttle since the tps wears down mostly in the light throttle positions. The ECM itself might be bad, or the EGR could be screwed up. Im not sure how to check out this EGR..... it has 3 solenoids and is nothing like the Fiero 2.8 EGR. One thing Ive noticed lately is that the EGR makes a loud click when you rev the engine up - Im guessing a solenoid is opening up after rpms start to climb down. I really dont think its a fuel delivery issue, as the engine has been running super rich and getting poor gas mileage (22 mpg). It just seems like its not getting the spark it should. I would like to replace the plugs and wires, but really dont have the money right now. I need a windshield pretty badly for the car, and all of the things that could be causing the hesitation would cost money to fix. Im kinda bummed out, as I was wanting to drive the car to school, but I really dont like driving it with this annoying hesitation. If anyone has any ideas, let me know! Thanks

quote Originally posted by toadson: I really dont think its a fuel delivery issue, as the engine has been running super rich and getting poor gas mileage (22 mpg).

I agree that it's not a fuel delivery problem in one sense: It's not that the car isn't getting enough fuel. Maybe, however, it IS a fuel delivery problem in that the car is getting TOO MUCH fuel.

I wonder, for example, if the injectors are too large for your application. What size are the injectors?

The injectors are the stock Lumina injectors. They havent ever been changed and are the stock injectors for this engine. Remember, I swapped the entire 3.1 out of the Lumina into my Fiero. I didnt use just the shortblock with the 2.8 intake and such. One thing to look at though if I were getting too much fuel, is the fuel pressure regulator.

quote Originally posted by toadson: The injectors are the stock Lumina injectors. They havent ever been changed and are the stock injectors for this engine....One thing to look at though if I were getting too much fuel, is the fuel pressure regulator.

I've found that with an engine swap in particular, an ADJUSTABLE fuel pressure regulator can be useful for tuning purposes, so yes, a regulator could be something to look into further.

Separately, if you know those are indeed the ORIGINAL injectors on the engine for your 1990 3.1L Lumina engine swap, the good news is you know those are the right SIZE injectors; the bad news is you also know those are 17-year-old injectors.

I wonder if those 17-year-old injectors are stuck partially open? It just seems odd that your car would run even worse with a new fuel filter, for example, unless it were already getting too much fuel in the first place, and the new fuel filter just helped to exacerbate the problem.

I honestly dont think is a fuel delivery issue, but Im not ruling out the possibility. Last night I got ahold of a tech 1 scanner, and it can manually do an idle relearn. I did the idle relearn 3 times, got the IAC in the right spec, and the hesitation is still there. The block learn value has been around 128, and I tested each EGR solenoid with the scanner. The TPS is smooth, and the map reacts as it should. The guy I borrowed the scanner from worked at a dealership for many years, and he really knows his stuff. He said that everything looked normal, and that I should swap in a stock PROM, do an idle relearn, and see if the problem is still there. I think that is my next step towards a fix. I think we have an ECM from a 2.8 cavalier 5 speed, but Im not so sure the prom will fit in my ecm. If not, I will run to the junkyard and fine another ecm to try.

I have a 3.1 5 speed that's swapped into my Fiero, and I'm experiencing almost the exact same problem. If I'm half throttle, she bucks like a kicking bronco... Idle is intermittent, but it runs smooth otherwise. You said you had the fuel filter out... I would replace the pump and injectors as well. That's what I'm going to be looking at here in the next little while.

I took the pump out from the Lumina and swapped into my tank, and I really dont think the pump is the problem. It seems to be getting fuel, but not enough spark. You said yours bucks pretty bad? Mine is actually driveable, but you have to rev it up a little more than normal when taking off and shifting. Its just annoying when you want to drive normally.

quote Originally posted by toadson: I took the pump out from the Lumina and swapped into my tank, and I really dont think the pump is the problem. It seems to be getting fuel, but not enough spark. You said yours bucks pretty bad? Mine is actually driveable, but you have to rev it up a little more than normal when taking off and shifting. Its just annoying when you want to drive normally.

Yeah mine is how you described... Mid throttle it bucks, but starting out you have to rev it to get it going... it's still driveable, but I constituted the problem to be a few things, it's either air, fuel, or spark... I changed the plugs and she stopped dropping a cylinder, I know she's getting enough air, so it's gotta be fuel. I'm going to check there next.

quote Originally posted by Leafy: I'm experiencing almost the exact same problem....You said you had the fuel filter out... I would replace the pump and injectors as well. That's what I'm going to be looking at here in the next little while.

This is beginning to sound like it has the makings of an interesting experiment.

Leafy, when you replace the fuel pump and the injectors, it would be interesting to see what, if anything, will happen to the engine problem you're experiencing --- especially if you replace only the fuel pump, or only the injectors --- first. Of course, if completing those two tasks ONE AT A TIME is more trouble than you feel it's worth, could you nonetheless then update us on the results of doing both replacements at the same time if that's what you'd prefer to do? Even if nothing happens to the engine problem after replacing the fuel pump or the injectors, reporting that in itself still should make for a more instructive thread.

toadson, I hope you'll continue to update us on your efforts to fix your engine problem as well, even if they take a different route.

I hope toadson doesn’t mind me leaving you guys a little update here since he is on vacation. After talking to a mechanic friend and hooking his tech1 scanner up to it we couldn’t really find anything out of place. His best advice was to try an idle relearn because the IAC counts were just barely in spec, and if that didn’t work he wanted us to try a stock Lumina prom and see what that changes (the current ECM is a DarthFiero tune). The relearn didn’t work, so Darth suggested that we look at the O2 readings when the engine acts up. They were disgustingly low, just as he predicted, so he is going to fix that in the programming.

Since it's the hot topic in another thread... how are your engine and chassis grounds?

It's worth noting that because this engine is stock, then a stock program should have worked fine (for a manual trans). The custom chip I made for Todd initially was based on a 1990 3.1L Vin T 5-speed car; which should have worked just as good as it would have in the original car. But then this tip-in lean hesitation issue came up; and since then I have tried increasing the AE (accel enrich) settings in the subsequent chips I made for Todd; but still the problem exists. Which leads me to believe the problem must be something in the wiring, with a sensor, or a mechanical issue. It could also be a bad ECM as I have seen several bad 7730 ECMs over the years do stuff like this. But I caution people who have problems like this to not run out and play the "swap till you drop" game with the sensors and other components. That game can get very expensive, and if the problem turns out to be something mechanical, something with the wiring, or possibly even some dirty injectors then you will end up replacing components and spending money you didn't have to.

As far as where to go from here; as someone suggested earlier checking the grounds would be a good idea. Make sure there are no broken or exposed wires hidden under the loom in the wiring harness as well and check for backed-out ECM connector pins/wires. With the engine running it would be a good idea to do a voltage drop test on the ground wires connected to the ECM. In order to do this you will need a digital volt meter capable of displaying/measuring DC battery voltage down to the hundredths (0.00) of volts. Then what you would do is put one probe on a clean spot on the engine and then run the other probe inside the car and backprobe the ECM connectors and check each engine ground wire at the ECM connectors while the engine is running. Basically you should never see any voltage show up on the voltmeter readout while doing this check (if you see anything it should be less than 0.1 volt). If something higher is found, it could indicate you have a bad ground connection at the engine or a broken wire in the harness.

Of course I would also check for vacuum leaks or exhaust leaks; anything that could cause a false or inaccurate signal to get to the O2 sensor. I am having Todd unplug the O2 sensor to see how the car runs without it; this could indicate the sensor he is using is bad or if it is getting a contaminated signal from a leak somewhere.


-ryan

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power corrupts. absolute power corrupts absolutely.

Custom Computer Tuning | Engine Conversions | Turbocharging | www.gmtuners.com

Wow, I had no idea I had all these replies until now, haha. Darth pretty much summed it up and the problem is still there. Just for the hell of it, I might grab another ECM, because I've heard of them going bad. I havent unplugged the O2 sensor yet, but I'll keep this thread up when I get some results.

I have a few updates for everyone on this subject. I tried unplugging the O2 sensor as Ryan said, and noticed no change at all in how the car ran. Even when cold it ran as if I had the O2 sensor plugged in. That really boggles my mind. I did a voltage drop test on the ECM ground wires and got a reading of .007, which is below the .01 volts Ryan indicated. I decided that I should add some ground wires today, and I think I have it all grounded pretty well now. I relocated my battery up front, and here is how I had my wiring:
For the front I had one ground wire running from the battery to the front crossmember. For the rear, I had one ground wire running from the cradle to the body, a ground wire running from the engine block to the body, a wire strap running from the decklid hinge to the top of the pulley mount bracket, and the ECM ground wires were connected to the body.
I added one wire up front from the battery to the body. In the back, I added a ground wire from the engine block to the cradle, and added a ground wire which runs from the ecm grounding spot on the body, to the top of the pulley mount bracket on the engine (same spot as the decklid hinge ground). I also cleaned up the ends on each ground wire and used copper paste to help conductivity. I didn't do a voltage drop test yet, but I noticed no improvement whatsoever in how the engine ran. As of yesterday, I discovered something that I haven't noticed before. When I hit the pedal to the floor as fast as I can, the engine chokes for a second and then revs up. Toaster_man noticed that a big puff of black smoke came out when it choked, and it smelled like carbon and gas. I'm really clueless as to what to try next, but he brought me another ICM and some coil packs to try. I guess that is the next step to this mess.

quote Originally posted by toadson: When I hit the pedal to the floor as fast as I can, the engine chokes for a second and then revs up. Toaster_man noticed that a big puff of black smoke came out when it choked, and it smelled like carbon and gas. I'm really clueless as to what to try next, but he brought me another ICM and some coil packs to try. I guess that is the next step to this mess.

Well if you are getting a black puff of smoke out of the exhaust upon throttle application then it is probably too rich -- which isn't a surprise as much as I turned up your AE (accel enrich) factors trying to correct the leanout issue you were having before. So at this point I recommend another chip with stock AE settings since this probably wasn't the problem in the first place.

-ryan

quote Originally posted by project34: when you replace the fuel pump and the injectors...

speaking of the injectors. Are these injector cleaners worth anything or can a "clogged" injector be fixed only outside of the car?

Ryan went ahead and set the program back to stock, so I am still trying to figure out a solution. I've replaced the spark plugs, plug wires, ICM and put on a different set of coil packs, which did nothing to fix the hesitation. I have been driving it to school, and its almost getting intolerable. The first minute or so of driving (cold start), results in a terrible hesitation when shifting from 1st to 2nd. The car almost dies sometimes, whether I ease into the throttle or not. It also hesitates every time I shift, even when its warm. It just seems worse when the engine is cold. I really wish I could get this problem figured out. It has been getting 30 mpg on the highway, but the hesitation just makes it no fun to drive.

quote Originally posted by Leafy: I have a 3.1 5 speed that's swapped into my Fiero, and I'm experiencing almost the exact same problem. If I'm half throttle, she bucks like a kicking bronco... Idle is intermittent, but it runs smooth otherwise. You said you had the fuel filter out... I would replace the pump and injectors as well. That's what I'm going to be looking at here in the next little while.

same problem with my 3.1 with fiero top end... i think i am gonna swap the injectors from my 2.8 and see if that helps... cause i have no clue what to do...

Maybe we should all just light our cars on fire. I'm about sick of mine. Damn 3.1's.

ok well i dont know if this will help yall but i have been playing with the idle air screw...(the last guy that had it messed with it first) i got it to idle great... but i still get horable gas mileage next i think i will swap the fuel rail and injectors from my 2.8 and see where that gets me... as i said before this 3.1 has about 1200 miles on it sense i put it together

If you have WINaldl running on a laptop hooked up to the aldl connector, you can see what your IAC counts are doing. As you probably know, the "Idle Screw" is not really used to set idle. The ECM controls idle through the IAC motor. The Idle screw is used to set the minimum opening of the throttle plate so it does not go past vertical and get stuck in the throttle bore. The factory did this and then sealed the hole with a plug. You are looking for an IAC count of 25-30.

WINaldl is free. Building a serial cable to hook up the laptop is cheap. If you only have USB ports on newer laptops you buy the whole cable already done for $40 or so.

quote Originally posted by Hudini: WINaldl is free. Building a serial cable to hook up the laptop is cheap. If you only have USB ports on newer laptops you buy the whole cable already done for $40 or so.

You could have problem with WINaldl finding the cable over the USB port. Still haven't figured out with mine.

Over the last few days, I removed the wiring harness from my car and went over it. I really cleaned it up and made it look nice, which is something I've wanted to do anyway. I found a few loose wires coming out of their connectors, and after fixing these, changing out the knock sensor and changing the knock sensor connector, the hesitation is still there. The only thing left to check in my mind is the fuel pump. Im not sure that changing it out would help anyway. Everything else I have done hasn't helped at all, so I'm thinking its hopeless.

I dropped the gas tank tonight and I might be onto something..... The inside of the tank is pretty rusty, and my town recently switched to 10% ethanol gas this summer. My dad mentioned that ethanol gas will clean rust off the inside of the tank, and it is doing exactly that. The fuel filter I changed a few months ago had a bunch of dark gas in it, and so does my new one that I checked tonight. The fuel pump sock is rusty colored, theres rust floating in the gas tank.... so yeah. Im sure this isnt helping things, so Im going to clean the inside of the tank with muratic acid. The stuff works great, as I cleaned out my old Kawasaki KZ1000 tank with it once before. Ill let you know how it turns out.

quote Originally posted by toadson: I dropped the gas tank tonight and I might be onto something..... The inside of the tank is pretty rusty, and my town recently switched to 10% ethanol gas this summer. My dad mentioned that ethanol gas will clean rust off the inside of the tank, and it is doing exactly that. The fuel filter I changed a few months ago had a bunch of dark gas in it, and so does my new one that I checked tonight. The fuel pump sock is rusty colored, theres rust floating in the gas tank.... so yeah. Im sure this isnt helping things, so Im going to clean the inside of the tank with muratic acid. The stuff works great, as I cleaned out my old Kawasaki KZ1000 tank with it once before. Ill let you know how it turns out.

We have always had the same problem with Dads 3.1 (2.8 block with 3.1 parts). Just a hesitation off idle that is always there. I hope you guys can find a solution. We have been trying with not luck either. FYI - Dont let that muratic acid touch any alluminum. Creates a nasty reaction and the alluminum will turn black. Sure does work great on brass and steel though. Works amazinly well on the contacts for the window and mirror switches.

I just fixed hesitation from idle problem on stock 88 formula 2.8/5sp.. Engine suddenly ran like crap so I spent all weekend troubleshooting before spending money. The engine idle ran up to 2000rpm, mis-firing, very rich,cloudy exhaust, and bad hesitation when tapping throttle from idle. On top of that there were no trouble codes. Did all the basic checks first: timing (10*btdc), grounds, fuel pressure (44psi), vacuum(20in at idle), voltage, plugs (very black), cleaned inside of distributor, cleaned throttle & IAC ( passed the IAC port blockage test ). After all that the engine still ran crappy. So next i checked TPS voltage & resistance which seemed work smoothly, Checked MAT voltage & resistance which was within range ( 4000ohms@60*F ). Then I checked the resistance of the CTS. At 60*F it read 33,000ohms. According to a table on the Meter thread it should have been around 3000ohms so it was 10x where it should be. So, I just bought a new CTS for $8.00, installed it, reset the computer and the engine started easily without peddle pressure. Idled up to 2000rpm for a few minutes and slowly dropped to 900rpm. Exhaust smelled cleaner, and NO MORE hesitation when tapping the throttle. After driving around the blocks a few times I would have to say that the problem was fixed.

SOLVED!
https://www.fiero.nl/forum/Forum1/HTML/067616.html
Thanks for all your help!

quote Originally posted by Amida: Then I checked the resistance of the CTS. At 60*F it read 33,000ohms. According to a table on the Meter thread it should have been around 3000ohms so it was 10x where it should be. So, I just bought a new CTS for $8.00,

Where is the CTS locatet?
Something I didn't check till now

Just below the t-stat housing on the lower intake manifold (marked ECM temp sender):


With everything mounted on the car it's a little crowded:

[This message has been edited by Hudini (edited 10-08-2007).]

Yes, the CTS is the one screwed in from the side. The one thing that I'm concerned about that may give me problems in the future is when I removed the distributor cap i noticed rusty flakes all over inside. It is coming from the iron pick-up poles which were just crusted & flaked with rust. I guess that is normal for a 19 year old car, but I can imagine it'll be a source for mis-fire. Can I buy shiny new pick-up poles or do I have to buy a whole new distributor?

[This message has been edited by Amida (edited 10-08-2007).]

New pick up poles? I would guess not because they changed the design later. All they do is make and break a magnetic field so it's not critical that they are shiny new. They cannot touch is all the FSM says. I would also guess rust flakes may cause touching.

The new replacement dist uses a star pattern which cannot be bent like the pick up poles. Jetman has a writeup on swapping the dist with a nice picture of the new one.

quote Originally posted by Hudini: With everything mounted on the car it's a little crowded:

Uhh oohh, yeah. Well I have to take a look at it when all it a little bit cooler than now...

Thanks for the perfect pics +

Just some food for thought.... I had a little trouble with my CTS. The wires were bare right where they met the connector, and they were wrapped around eachother, causing it to read some crazy values. I unpinned each wire and used heat shrink tubing, and now it works perfectly fine.