Greetings to all, Haven't been on the forum for some time. I've been successful in keeping several Fieros belonging to family and friends running well for quite a few years now...until now. This 86 GT 2.8 has gotten the best of me, so I am hoping someone here might have an idea of what to do next. Here's the symptom: Lots of power until car warms up, then power cuts way back, car keeps running, but backfires through exhaust. Attached remote vacuum gauge and fuel pressure gauge. Fuel pressure is constant at 45 psi, but vacuum drops to near zero when power is lost. I haven't figured out if that is a symptom or a cause. Vacuum runs steady at about -16 psi at idle. This car has 140,000 miles on it, but it should be running like new...20,000 miles ago I put in new main and rod bearings and a high volume oil pump. New water pump, new thermostat and temp sensor and fan switch. It has had Mobile One full synthetic oil in it since then and makes 40-50 psi at idle and 70+ psi on the highway. Does not burn oil. Replaced all exhaust gaskets and catalytiic converter. The car has run well since then (about 4 years ago). Fast forward to the present issue... Here's what I've done to try to fix it: Dropped exhaust system to make sure there were no restrictions....even ran water through it, then replaced the cat again because I don't trust cats (just dogs). No cat pieces rattling in muffler. Replaced MAP sensor, substituted IAT sensor, TPS and replaced O2 sensor (twice). Did fuel rail pressure bleed-down test...it passed...holds pressure as per manual. Used the WINALDL scan tool and found that system reports a constant rich condition. Checked timing....checked TDC on cylinder #1 to verify ring on damper pulley hadn't come loose and moved. It hadn't. Verified base timing set to 10 deg BTC. Rebuilt distributor with new spark control module, shims, coil, rotor and cap. Checked for timing chain slop (it's new, but I checked anyway, and it's good). Timed it again. Replaced coil. Replaced wiring and connectors around coil that showed signs of heat damage.
....and now, it has the same symptom I started with. All of the used parts that I pulled off of the car are going on the shelf as used/good. It's a good thing I'm not a doctor because I'm losing my patients (patience...oh well!)! . After having several of these little engines torn down and reassembling them successfully, this one has rocked my confidence! This is a beautiful looking little car that used to run strong, as Fieros go. Any ideas on what I may have overlooked?
Your inputs and opinions would be greatly appreciated
Thanks in advance! ~~Dan
------------------ Gold '87 GT auto, Black '86 GT 4spd, Black '87 GT 5spd, Black '88 Mera #8085,' 64 Stingray coupe, '01 Corvette coupe, '03 Corvette coupe & caretaker of son's Yellow '87 GT, & Other son's Red '86 GT, General tinkerer and doer of mechanical deeds
PS.... Also replaced the EGR valve and the EGR actuator assembly with new components... and EGR tube. + all vacuum lines are steel replacements (pretty, but a pain to fit!).
Your computer is asking for too much fuel. It will read the sensors to make that calculation, namely the Coolant Temp Sensor, which is different than the Temp Gauge sensor. Did you replace them both? Sometimes new parts are not good parts.
If all that is OK, I would think about swapping another ECM if you have one.
Thanks! I will try those items next, as I haven't replaced either. I have a couple of extra ECM's and a new coolant temp sensor. Should have time to try these on Sunday.
If it works I will be designating you as a genuine A#1 hero! ~~Dan
When running WinALDL, what type of temperature readings are you getting from the IAT and CTS when the engine is cold (like first thing in the morning) before you start the engine? The temperature readings should both basically be the same as the overnight temperatures in your locale. Once the engine is started, the IAT readings shouldn't change a whole lot (if any), and the CTS reading should steadily climb to around whatever temperature your thermostat is. What temp thermostat are you running?
Patrick, if there is a 9 degree temperature difference between the sensors (when cold before start) would this indicate that the coolant temp sensor is faulty?
Patrick, if there is a 9 degree temperature difference between the sensors (when cold before start) would this indicate that the coolant temp sensor is faulty?
Why do you suspect the CTS more so than the IAT sensor?
I don't know if a 9°F difference is significant or not. Possibly not.
It's been awhile since I checked mine, but it seems to me the readings for my CTS and IAT were closer to each other, probably within a couple of degrees. Keep in mind though that if you take your readings after the ambient air temperature starts to rise in the morning, the IAT readings will no doubt be higher than the CTS readings (as it takes much longer for the rising ambient air temperature to increase the coolant temp).
[This message has been edited by Patrick (edited 06-08-2015).]
Patrick-- thank you very much for the information. I was suspecting the CTS because the AIT is brand new and it did not change the performance of the car. We tried it at about 9am if I remember correctly. Maybe another look is needed to see if it is indeed off. Is it not very common for the CTS to be bad compared to the AIT?
Do the spark plugs look rich or do they look lean?
No exhaust leaks?
I am wondering if for some reason the O2 sensor is reading rich cuasing the ECM to lean out the mixture and reduce power. Until the O2 sensor is warm the ECM ignores this input. Is this engine running lean or rich by looking at the plugs. If lean as I suspect then the thing to look at is why is the O2 sensor reading richer than it should.
[This message has been edited by phonedawgz (edited 06-08-2015).]
Is it not very common for the CTS to be bad compared to the IAT?
I don't know how common it is for either one of them to fail (I've never had a bad one on five Fieros in over 20 years), but I have read of them failing here at PFF. The "test" I suggested was just an easy way to see if one or the other was way off. I'm definitely no expert when it comes to the ECM and associated sensors.
APhonedawgs, I have put two brand new ( one ACDelco, one Bosch) O2 sensors in the car at different times. At this point I have no idea why it is running like a lawn mower and heating up so fast. I don't believe either one to be faulty at this point, but I did do that test you suggested before and it didn't seem to affect the symptoms. I just replaced all the spark plugs with OEM Delco replacements, and replaced the wires with Bosch wires after having hooked up an osilloscope to them and finding two that were bad. The oscilloscope reads evenly spaced peaks with even amplitudes now, but the over heating, intermittent misfire and power loss while driving still exists. The plugs were all white except cylinder 3 which was black (this is the one that we thought was likely bad/ intermittent after the oscilloscope test). Also, the fuel injectors are all brand new as of a couple weeks ago, no change to performance.
If you guys didn't catch it yet, GMplastic is my Dad we've both been working on this car since last August and are for the first time one Fieros, completely stumped though :/
Patrick, We will likely test/ swap out the sensor soon (they are only $15, so might as well try it ).
Edit: the car seems to be running rich, right off of start up. It smells rich and burns the eyes terribly. Also the miss fire problem is both when the car is cold and when it is hot. The power loss seems to be only when it is hot and under load.
[This message has been edited by LaFierte (edited 06-08-2015).]
So, this weekend GMplastic (Dad) and I got around to replacing the coolant temperature sensor. I the process I found and fixed a vacuum leak that was in the brake booster line, so all line have been replaced now. We still have the same problem. We are now looking at possibly a stretched or skipped timing chain. Is there anyway of telling if this is the problem for sure?
We are now looking at possibly a stretched or skipped timing chain. Is there anyway of telling if this is the problem for sure?
A stretched timing chain can be determined by turning the crank backwards and measuring how far it rotates before the distributor rotor starts to turn. Off the top of my head though, I don't know how many degrees of rotation (before rotor movement) are considered "normal".
Ok, there doesn't seem to any discrepancy between when the balancer starts to turn and the rotor on the distributor starts to turn. Any thoughts/ suggestions on where to go from here?
Yes, we tried this a couple times without noticing a difference, although it is hard to keep your eye on both the crank and the distributor at the same time. Maybe I can try it again a couple times just in case, but it seemed to have no slip to it to us last night. We also tried listening for chain slap with a mechanics' stethoscope both while turning the crank and while the car was running. All we could hear was the fins of the water pump pushing water.
You've found one spark plug (#3) that was black. Try the leak down test again key on, engine not running. I wonder if that injector is grounding out, keeping open all the time?
Its been solved!!!! We discovered it to be a partially failed distributor pick-up coil that was confusing the ICM and telling the fuel injectors to fire at the wrong time. Usually when they go bad the car just won'n run, but this was a rare case of partial failure. Several months later.... a $15 part....
One thing I did when the intake was off was clean out the EGR tube opening (because it was plugged with carbon and oil deposits). Now the top of the intake is getting so hot that you can't hardly touch it without getting burnt. Is this normal or is the EGR sticking partially open (the car still lacks the get up and go it used to have -- though it doesn't suddenly lose all of its power)????
One thing I did when the intake was off was clean out the EGR tube opening (because it was plugged with carbon and oil deposits). Now the top of the intake is getting so hot that you can't hardly touch it without getting burnt. Is this normal or is the EGR sticking partially open (the car still lacks the get up and go it used to have -- though it doesn't suddenly lose all of its power)????
With the engine cold, stick your fingers in the hole on the bottom side of the EGR valve, and feel if it is stuck. It should slide up and down with finger pressure.
Well it works, I cleaned it anyway. Found a vacuum line that had popped off so fixing that helped. Still running hot, still sluggish. It's an odd feeling of the car wanting to dig in and go and at the same time not while driving it. Apparently there is more wrong with it than just the pick up coil. Anyone have any ideas?
One thing I did when the intake was off was clean out the EGR tube opening (because it was plugged with carbon and oil deposits). Now the top of the intake is getting so hot that you can't hardly touch it without getting burnt. Is this normal or is the EGR sticking partially open?
A couple of months ago I had the upper plenum off of my '88 Formula to swap in rebuilt injectors. I discovered that my EGR tube was both plugged and cracked. When I replaced the EGR tube (with one from a Camaro) I then discovered that the top of the upper intake seemed to be getting a lot hotter than I remember it used to. This concerned me as well. However, my 2.8 doesn't appear to have any performance issues, so I guess the hot upper plenum is "normal".
Ah thank you very much Patrick. I was a little worried there. I think I found the problem with it being sluggish tonight as well. The Harmonic balanced slipped slightly. So the car wasn't timed quiet right. I'm looking at getting a kit to fix it.... Are there assembly marks on there so I can tell if I have the two pieces aligned right?
The Harmonic balanced slipped slightly. So the car wasn't timed quiet right. I'm looking at getting a kit to fix it.... Are there assembly marks on there so I can tell if I have the two pieces aligned right?
A kit to fix it...? I don't think so. You need to replace it. Been there, done that.
Yeah, I was looking at getting a rebuild kit with the rubber and glue stuff since I'm fairly mechanically savy. Is it just very difficult to get it in the right place? Or do the kits not last long? I wonder the person with the link to rebuilt ones was using.... I can get a new one, but I'm trying to save for college, so I have more time than money.
Yeah, I was looking at getting a rebuild kit with the rubber and glue stuff since I'm fairly mechanically savy. Is it just very difficult to get it in the right place? Or do the kits not last long?
Post a link to what you're referring to. The only "rebuild kit" I'm aware of for the Fiero harmonic balancer is basically a sleeve that covers the groove that the oil seal makes after a couple of decades.
That is why I was asking about other places. Seemed a little sketchy that it was named wrong. I'll let you all know how it goes with ordering from there.
we've both been working on this car since last August and are for the first time one Fieros, completely stumped though :/ 
