Reminder to not rule out new parts when troubleshooting (Page 1/1)
Weatherguy717 MAR 27, 09:16 PM
After my original engine blew up due to a slipping transmission, the replacement engine left much to be desired. Poor throttle response and slow acceleration let me know that something was wrong. Pulling off the distributor let me know there was lots of rust and I figured to replace it for peace of mind. Replacing it with a new one and redoing the timing really woke up the 2.8L after what I was used to, but had a problem with misfiring/backfiring with sustained RPMs of 2000-3000. Idle and higher RPMs were fine, but sustaining that RPM would lead to misfiring. I tested the TPS, tried a new TPS, tried a new IAC, replaced O2 sensor, checked spark plug gap, tried advancing the timing, tried retarding the timing, tried a new MAP sensor, checked for vacuum leaks, replaced all intake gaskets, replaced vacuum lines with Rodney Dickman's stainless steel lines, checked to make sure the harmonic balancer mark didn't slip, changed ICM, and changed spark plug wires all to no avail. After three days of painstaking troubleshooting I figured to replace the new distributor with the old one to make sure it wasn't bad, and what do you know? The brand new distributor (or coil) was bad! The reason for the poor throttle response and slow acceleration in the first place is because the previous owner of the engine didn't jump the ALDL port when timing, so the ECM was advancing the timing to where it should have been in the first place. Let this be a reminder to not rule out new parts when troubleshooting! Now with that out of the way I can drive this one and work on getting my other Fiero painted for the 40th.
Patrick MAR 27, 10:02 PM

quote
Originally posted by Weatherguy717:

Pulling off the distributor let me know there was lots of rust and I figured to replace it for peace of mind.



The rust is normal. It's due to the ozone being produced inside the distributor cap. This was what my distributor looked like at one point, before I cleaned it up a bit.




quote
Originally posted by Weatherguy717:

The reason for the poor throttle response and slow acceleration in the first place is because the previous owner of the engine didn't jump the ALDL port when timing, so the ECM was advancing the timing to where it should have been in the first place.



I don't quite follow you (although this might be what you're saying)... but if the ALDL terminals aren't jumpered while setting the timing (which eliminates all ECU ignition advance), the ignition timing (when un-jumpered) will be far too retarded.

You bring up a good point though... never trust new parts!

[This message has been edited by Patrick (edited 03-27-2023).]

Raydar MAR 28, 11:03 AM
Exactly this!
Several of the folks in our club went nuts trying to get one of the club members' 4.9 "sorted". Lots of stuff had been replaced, but it still stumbled, misfired, and just generally ran poorly.
The "newly replaced" distributor was removed and replaced by a parts yard unit, and everything cleared up. The "replacement" distributor had the cam sensor installed incorrectly, and was doing... strange things to the timing.
Weatherguy717 MAR 28, 08:02 PM

quote
Originally posted by Patrick:

I don't quite follow you (although this might be what you're saying)... but if the ALDL terminals aren't jumpered while setting the timing (which eliminates all ECU ignition advance), the ignition timing (when un-jumpered) will be far too retarded.

You bring up a good point though... never trust new parts!




Yes this is what I meant, whoever worked on the engine previously did not jump the ALDL ports when timing the engine, so the ECM was advancing the timing to the 10 degree mark at idle, and retarding it when in drive. Honestly I'm surprised it even drove with the timing that far retarded.
Patrick MAR 28, 11:01 PM

quote
Originally posted by Weatherguy717:

...whoever worked on the engine previously did not jump the ALDL ports when timing the engine, so the ECM was advancing the timing to the 10 degree mark at idle, and retarding it when in drive.



Ummm, I'm still not sure you've quite got it. If the ALDL terminals are not jumpered when the ignition timing is set, the timing is too far retarded at all RPMs. Keep in mind that with the ECU advancing the ignition timing, the advance is far higher than 10° BTDC at idle when it's been set properly.
reinhart APR 24, 07:52 AM
All "new" distributors come with garbage IMs. I bought one to get the new star rotor design expecting the IM would not last long. I left it in there just to see though. Within a week it failed on a busy highway. I of course had a new GM module handy. Replaced the "new" chinese IM with the GM one on the shoulder of the highway and it's been in there for 5 years no problems.
sleek fiero APR 26, 10:52 PM
Talk about new parts I got a temp sensor/idiot light switch from the Fiero store and the gauge worked fine but the idiot light would come on after a couple of minutes. I removed it and checked with ohm meter. It was open circuit until I warmed it to 103 Fahrenheit and it closed. Got another Standard TS-168 and checked it and it did not close until 218 Fahrenheit. Pays off to check new parts before install. sleek
reinhart APR 28, 03:15 AM

quote
Originally posted by sleek fiero:

Talk about new parts I got a temp sensor/idiot light switch from the Fiero store and the gauge worked fine but the idiot light would come on after a couple of minutes. I removed it and checked with ohm meter. It was open circuit until I warmed it to 103 Fahrenheit and it closed. Got another Standard TS-168 and checked it and it did not close until 218 Fahrenheit. Pays off to check new parts before install. sleek



2 in a row is pretty bad. Can you tell what brand FS is selling?
AustinH APR 10, 09:58 AM

quote
Originally posted by Weatherguy717:

After my original engine blew up due to a slipping transmission, the replacement engine left much to be desired. Poor throttle response and slow acceleration let me know that something was wrong. Pulling off the distributor let me know there was lots of rust and I figured to replace it for peace of mind. Replacing it with a new one and redoing the timing really woke up the 2.8L after what I was used to, but had a problem with misfiring/backfiring with sustained RPMs of 2000-3000. Idle and higher RPMs were fine, but sustaining that RPM would lead to misfiring. I tested the TPS, tried a new TPS, tried a new IAC, replaced O2 sensor, checked spark plug gap, tried advancing the timing, tried retarding the timing, tried a new MAP sensor, checked for vacuum leaks, replaced all intake gaskets, replaced vacuum lines with Rodney Dickman's stainless steel lines, checked to make sure the harmonic balancer mark didn't slip, changed ICM, and changed spark plug wires all to no avail. After three days of painstaking troubleshooting I figured to replace the new distributor with the old one to make sure it wasn't bad, and what do you know? The brand new distributor (or coil) was bad! The reason for the poor throttle response and slow acceleration in the first place is because the previous owner of the engine didn't jump the ALDL port when timing, so the ECM was advancing the timing to where it should have been in the first place. Let this be a reminder to not rule out new parts when troubleshooting! Now with that out of the way I can drive this one and work on getting my other Fiero painted for the 40th.



Hey man, saw you were having more issues with your drivetrain. Wondering if you would be interested in selling the body, no engine. Let me know, thanks!
hyperv6 APR 10, 03:25 PM
When it come to Chinese parts it really matters where it is made.

We have parts made in China at work. The trick is you have American QA people in the plant 24/7.

The plants that have little to no supervision will do what ever and test is where the trouble starts.

Companies like Apple will keep people in house watching I phone production too. I saw not long ago one plant was caught subbing in lower quality screens.

So while some parts may be junk others can be great. Just depends on what oversight they have.