Hey all, my 88 formula is currently getting around 11mpg without ac running. It used to get around 19 but after I let the car sit for 2 months it dropped down to 11. The only thing that changed was my exhaust blew out more on both sides of the catalytic converter, would this cause such a large loss of fuel economy? Car idles around 900 rpms, no SEL or decrease in power. Any ideas? Of course I plan on replacing the exhaust but I’m tight for money and time currently so if that won’t fix my issues I’ll have to find something else to drive. Thanks
The 02 sensor can be reading a false lean condition because of holes in the exhaust. The computer adjusts by adding more fuel...and more fuel...but it's never enough.
Originally posted by Gall757: The 02 sensor can be reading a false lean condition because of holes in the exhaust. The computer adjusts by adding more fuel...and more fuel...but it's never enough.
Yup, any exhaust leak can cause between head and O2 and down to the cat can cause very rich engine getting crap MPG.
ECM only sets codes 44 or 45 when both BLM and Integrator are Pegged and stay there for some time. BLM can stay Pegged for days w/o setting codes when Integrator can move even 1 number off of pegged. More See my Cave, Scan Tool Help
That's assuming you don't have fuel leaks, injector problems, etc.
------------------ 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)
Unplug your o2 sensor and disconnect the battery. Tie up the o2 sensor wire so it doesn't burn on the exhaust. Reconnect the battery. See if that brings your mileage back. If so, yes your o2 sensor is driving the loss in MPG. If not, time to look elsewhere.
Is the entire stainless steel factory exhaust rotten (very doubtful), or is it just the short mild-steel lengths of pipe on either end of an aftermarket cat that have rotted?
[This message has been edited by Patrick (edited 05-05-2022).]
Is the entire stainless steel factory exhaust rotten (very doubtful), or is it just the short mild-steel lengths of pipe on either end of an aftermarket cat that have rotted?
Is the entire stainless steel factory exhaust rotten (very doubtful), or is it just the short mild-steel lengths of pipe on either end of an aftermarket cat that have rotted?
Cat is fine, headpipe is blown out on one side and the pipe leaving the cat is blown out too. Muffler has also split on the side facing the trunk.
Cat is fine, headpipe is blown out on one side and the pipe leaving the cat is blown out too. Muffler has also split on the side facing the trunk.
Poor fuel mileage can be caused by a dozen reasons. clogged cat, defective O2 sensor (or other sensors), stuck open injector, defective thermostat, leaking cold start injector, ignition problems (or miss), and severe engine wear. The only way to tell is by doing all of the checks item by item.
------------------ " 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 "
Hey Kyle....my sons 88 fiero got 11 mpg as well. It was terrible. We found out that one of the injectors was bad. I replaced the broken one and cleaned the rest. This got him up to around 13-14 mpg. I did a coolant flush due to the crazy cold snaps we have been getting down here in Texas and not wanting his new radiator, and heater coil to splode cuz we had water in the system. While doing this I noticed there was no thermostat in the car (it was missing in my 86 as well....weird). Anywho I replaced it and the car gets to operating temp WAY faster. On cool days the heater would normally not work until I got where I was going. The car was staying in warm up (rich) mode basically for the entire drive....every drive. After replacing the thermostat I regularly get 15-17 mpg with a light foot and I guess around 20 highway. Maybe something to check. BTW I enjoy your videos. Keep up the good work.
Originally posted by Dennis LaGrua: Poor fuel mileage can be caused by a dozen reasons. clogged cat, defective O2 sensor (or other sensors), stuck open injector, defective thermostat, leaking cold start injector, ignition problems (or miss), and severe engine wear. The only way to tell is by doing all of the checks item by item.
Add Iffy ECT or wires to it. ECT was upgraded to Metripack plug (88 should have the upgrade) because old plug was giant pain and can a lot of headaches.
Do you have access to a scan tool?? Any codes showing? To check for a blown injector , secure a fuel pressure gauge an attach it to the schrader valve fitting on the fuel rail. At idle the pressure should be around 43.5 PSI. If the pressure drops quickly when you turn the engine off that indicates a fuel injector or cold start injector problem. If all is good then check the ETS/CTS sensor. Only a scan or a resistance check in hot water will check it. IMO, those are two of the most likely possibilities
------------------ " 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 "
Dennis beat me to it. If you have access to a scan tool, look at the Coolant Temp (CTS) and the Intake Air Temp (IAT) readings. Look for anything that seems to be "too cold". (CTS should reflect reasonable engine temp. IAC should be "ambient" air, or maybe a bit warmer.) These will be separate sensors from your gauge sender. The gauge will not be an accurate representation of anything but the gauge sensor reading.
[This message has been edited by Raydar (edited 05-11-2022).]
