PFF - Pennock's Fiero Forum, PDA Edition

When warmed up fiero doesn’t want to go over 35 mph (Page 1/3)

Monroefiero1986

DEC 23, 03:01 PM

I’m brand new to this forum and am looking for some opinions on why my 1986 sport coupe 4 cylinder only wants to top out at about 35 mph and gets jerky when I apply the throttle. This only happens when the car is warmed up. If I put it in neutral and rev the engine the rpm’s are smooth. And it idles in park good too. I’ve verified that all the vacuum lines are connected good. I put a new EGR, IAC valve, map sensor and fuel pump in a couple months ago, and it’s been running good up until about 2 weeks ago. So I don’t believe any of them were faulty at the time of installation. Could the TCC solenoid be the culprit? Any feedback would be greatly appreciated.

fieroguru

DEC 23, 03:48 PM

Sound like it is running out of fuel. The hose from the pump to the fuel supply line could have come loose of been the wrong type and developed a hole.

Fuel pressure gauge will be your friend, but you will have to make some adapters to splice it in.

82-T/A [At Work]

DEC 23, 08:02 PM

I concur with FieroGuru... that sounds like a fuel problem.

I had the same thing with a 1973 VW Bus. There were little holes in the air line BEFORE the pusher pump... it was sucking air through the worn out rubber hose, so it wasn't feeding enough fuel to the engine. I couldn't get it to go over 35 miles an hour, and it took FOREVER. I replaced it with steel lines, and I was magically doing the top speed of 70 miles an hour.

With your Fiero, it could either be the little hose between the fuel pump and the sending unit, or the pump is failing.

Dennis LaGrua

DEC 23, 08:54 PM

Check all the fuel lines, replace the fuel filter, insure that that the fuel injector is clean, not clogged, test the pressure that the fuel pump is putting out. Fuel pressure should read about 15 psi.

------------------
" 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 "

fierofool

DEC 24, 10:00 AM

A disintegrating catalytic converter can create the same symptoms as the pieces can clog the exhaust pipe or muffler. It will idle and rev without problems but won't pull itself out of its own shadow.

Vintage-Nut

DEC 24, 11:36 AM

My GT is on the third catalytic converter..........

------------------
Original Owner of a Silver '88 GT
Under 'Production Refurbishment' @ 136k Miles

Dennis LaGrua

DEC 24, 09:39 PM

quote

Originally posted by fierofool:

A disintegrating catalytic converter can create the same symptoms as the pieces can clog the exhaust pipe or muffler. It will idle and rev without problems but won't pull itself out of its own shadow.

Didn't think of that but its an excellent point. Never has this problem as my Fieros don't have them but they are all used off road only. Nothing like the old fashioned straight pipe for optimum performance, a cooler running engine compartment and a reduced fire hazard.

------------------
" 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 12-24-2024).]

fierofool

DEC 25, 01:11 PM

quote

Originally posted by Dennis LaGrua:

Didn't think of that but its an excellent point. Never has this problem as my Fieros don't have them but they are all used off road only. Nothing like the old fashioned straight pipe for optimum performance, a cooler running engine compartment and a reduced fire hazard.

One of my 85s converter broke apart and clogged the muffler. I had a 40 mile drive home on the Atlanta interstate. Fortunately, rush hour traffic doesn't get more than 20 mph but it was still a struggle. My daughter's Santa Fe lost power and wouldn't even pull itself up on a tow dolly. It would idle and rev beautifully. She sold it to a friend for $600. The friend's father replaced the converter and last I saw they were still driving it three years later.

Dennis LaGrua

DEC 29, 07:19 PM

A good temporary fix is to drop the CAT and with a tire iron going through the inlet/outlet openings crack out the inside mesh and pour the contents out. You can re-install drive this way and be quasi legal as in theory your Fiero will still have the CAT. This also removes a potential fire hazard.

Patrick

DEC 29, 07:32 PM

A plugged cat is a good suggestion (I've had it happen to my '86 GT), but the symptoms were the same whether the engine was hot or cold. Keeping the OP's comments in mind, I suspect the OP's problem is a fueling issue.

quote

Originally posted by Monroefiero1986:

...my 1986 sport coupe 4 cylinder only wants to top out at about 35 mph and gets jerky when I apply the throttle. This only happens when the car is warmed up.