First time posting, I've been using this site as a resource for years. Thank you for your information. My question/problem involves my 1984 Fiero with a stock iron duke. The car starts, runs, and idles fine until it gets to 3,800 RPM. Once it gets there the engine begins to sputter and lose power until I back off the throttle and get the RPMs down, then it is ok again. Recently, (summer 2018) during an acceleration I allowed it to remain above the "3,800 limit" and the oil pressure switch let loose and the engine pumped oil straight to the ground through the hole in the oil sending unit.
I've searched the site and gathered information about the oil switch providing power to the fuel relay and all the opinions about the reasons. As far as I can tell the car is losing fuel pressure at 3,880 for some reason, (maybe the fuel pump and the oil switch are cutting out in that moment)?
Engine is still ok and I replaced the oil switch. All is normal except it still can't be run above 3,800 RPM. Do you have any idea what is happening and how to fix it? Thanks all, Sam
First replace the fuel filter . If that's not impeding the fuel flow, it really sounds like a plugged up/clogged CAT. Is the CAT original to the car?
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
[This message has been edited by Dennis LaGrua (edited 02-13-2019).]
Thank you for the suggestions. I will look into it. I believe it is still the original CAT.
A CAT that old is likely to have collapsed internally and caused a restriction. . Its a common problem on these cars. That's the reason many don't use them.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
Any HEI park weak or Fuel problem can do this. Iffy HEI timing doesn't help.
84 coil needs good ground to engine block via mounting hardware. Coil can be updated but need 85 plug. Don't brother w/ any "performance" coils including Accel and MSD. Get Standard or Wells or best store brand thru local stores. Example AZ HEI parts are often Wells parts.
OE Duke uses "pebble bed" cat and won't plug most times. Not like monolithic cats that easily plug or break. If the "bed frame" inside fails then pebbles might move and plug the muffler. easily check of iffy exhaust w/ exhaust pressure gauge reads ~ 5 - 8 PSI max. quick example from google search https://www.amazon.com/Tool...essure/dp/B0002SQW9S
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
1984 Fiero with a stock iron duke. The car starts, runs, and idles fine until it gets to 3,800 RPM. Once it gets there the engine begins to sputter and lose power...
How have you confirmed this "3,800 RPM"? You can't trust the 35 year old factory tach.
Keeping in mind the red line on the duke is only 4500 RPM, perhaps you're actually over-revving it.
Originally posted by Patrick: How have you confirmed this "3,800 RPM"? You can't trust the 35 year old factory tach.
Keeping in mind the red line on the duke is only 4500 RPM, perhaps you're actually over-revving it.
Yes, can't trust many dash gauges not just the tach for even newer cars. Scan the ECM or use a "Shop Tach" to see if Dash Tach # are real.
Many Brand New cars still use resistivity senders/sensors for fuel and temp gauges even tho dash is run by BCM and/or PCM (ECM w/ full trans control) so gauges can lie when have sender or wiring problems.
"I've searched the site and gathered information about the oil switch providing power to the fuel relay and all the opinions about the reasons. As far as I can tell the car is losing fuel pressure at 3,880 for some reason, (maybe the fuel pump and the oil switch are cutting out in that moment)?"
To clarify how this circuitry works....
The power for the fuel pump is provided via two sources, the fuel pump relay and the pressure switch in the oil pressure sending unit. The power is provided to both via the fuel pump fuse with the key ON. During initial KEY ON, the ECU signals the fuel pump relay to energize for a few seconds to pressurize the fuel system, and then when the ECU detects engine start, the ECU re-energizes the fuel pump relay and keeps it energized to run the fuel pump continuously. When oil pressure rises, the pressure switch in the oil pressure sending unit closes, also providing a power source for the fuel pump. This redundantcy allows the fuel pump to operate if the fuel pump relay fails. The pressure switch in the oil pressure sending unit WILL NOT kill the fuel pump if oil pressure drops, as the ECU has the fuel pump relay energized continuously during engine operation. Additionally, if the fuel pump relay fails, the pressure switch in the oil pressure sending unit allows the fuel pump to operate as long as there is oil pressure, in order to allow the car to continue on, avoiding a breakdown. The car will also restart, although the cranking period will be longer, as the engine must build oil pressure to close the pressure switch to activate the fuel pump.
I hope this helps in the understanding of this circuitry.
[This message has been edited by olejoedad (edited 02-15-2019).]
