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1995 GM pops and hesitates under hard acceleration

Old 11-14-2017, 08:51 PM
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Default 1995 GM pops and hesitates under hard acceleration

Just picked up a nice 95 GM LS 4.6 with handling pkg 69k orig miles, car idles and runs smooth unless you floor it then pops and sputters a bit. I cleaned MAF with correct spray also cleaned TB, changed air filter, pcv and spark plugs. Problem better but not gone. Also noticed the clamp for the hose to TB connection is missing but its pretty tight even W/O the clamp so not sure if it could be pulling any outside air. Only thing I did not do yet is fuel filter. Any ideas? Thanks

Last edited by Joe308; 11-14-2017 at 08:57 PM. Reason: Fix
Old 11-20-2017, 01:07 PM
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Location: Phoenix, AZ., USA
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Default Stumbling and Hesitation

You will need a new Throttle Position Sensor and a new Idle Air Control Valve.
Get the genuine Motorcarft parts to be sure of a perfect fit and function. Both can be had for a low price from or
The TPS can be replaced easily by removing the Throttle Body, removing the TPS, and replacing it with the new TPS. No gasket is required,
but you will need two (2) new screws ( M5 x.08 x 30mm) to do a proper job.
The IAC (motor-driven) valve will need a new gasket, and the gasket is EASY to install if you GLUE IT IN PLACE before attempting to fit the valve to the engine.
I used Loctite Spray Adhesive, applied to the rough side of the gasket before gluing the gasket to the valve.
After the gasket is glued in place, let it dry for 10-15 minutes before fitting the valve to the engine.
DO NOT attempt to "adjust" or "tune" the TPS or the IAC valve -- the computer controls both, and it will pull all settings into factory specs, all by itself !!
As for the fuel system -- your in-tank fuel filter is probably OK, but the in-line filter that's under the car on the driver's side, should be replaced with a new Motorcraft FG800 fuel filter.
I use Chevron "Complete Fuel System Cleaner" (The 20-oz size is just right for the 20-gallon tank) to remove any varnish/deposits from the fuel system, and especially the fuel injectors,
which are prone to getting gummed-up from the ethanol gasolines.
If you suspect water in the gas, the best water-remover available is "ISO-HEET" -- it contains Isopropyl alcohol, which performs much better than the cheap stuff.
If this all sounds too expensive, just remember that you can save a bundle by getting your parts from Rockauto or Amazon, and doing the work yourself.
Nothing difficult or complicated -- just take your time and do it right.
Good Luck !!
Old 11-20-2017, 02:29 PM
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I sprayed out the throttle body again and replaced the clamp on the air inlet tube that was missing. Also ran 2 tanks of fuel thru with Techron and prob seems to be gone. Still want to change filter but its a pia to reach w/o a lift. I will keep the orher items in mind but don't think their replacement is necessary at the moment. Do you work for Rock Auto?
Old 11-22-2017, 01:54 PM
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Location: Phoenix, AZ., USA
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Default Stumbling and Hesitation

I buy the Chevron "Techron Complete Fuel System Cleaner" by the case, and add a bottle every 5,000 miles (at oil filter change). It ain't cheap, but it works better than anything I've ever found.
I'm curious about that "clamp on the air inlet tube" - can't figure out which tube you are talking about. Both of the tubes attach to the plastic air intake box, but they are part of the PCV system.
Anyways, if you're happy, I'm happy !!
And, NO, I don't work for RockAuto -- or Amazon, either. I've been retired from the printing industry for 20 years. I recommend them both, but for different reasons.
RockAuto almost always has the best prices, and Amazon's fast and free delivery makes it a top choice when time is important.
I noticed that yours is a '95 Grand Marquis, so I was immediately interested, and here's why: I have A LOT of time and money invested in my '95 Merc, and I've learned A LOT about the car's maintenance, performance, and handling. I do my own work -- at home, in the carport. I've had the car for 12 years, and it now has 153,500 miles on the clock. The modifications I've made have given me a top-performer under city/highway/freeway/mountainous conditions.
Perhaps you can benefit from my extensive experiences with the '95 Grand Marquis:

1995 Grand Marquis Restoration.
Engine is basically stock, with no internal modifications.
Items marked with "#" are/were available for purchase at

Intake Air Box Snorkel removed - cool air is ducted from forward of the engine compartment.

# K&N *33-2272 Re-usable Air Filter.
# Bosch *69128 Electric Fuel Pump.
# Bosch *68015 In-Tank Fuel Filter
# Mallory *4213 Adjustable Fuel Pressure Regulator -- 35 psi. @ 800 rpm.
# Bosch *4809 Series 3 - 19 lb. Fuel Injectors.
# Bosch *09725 Mag-Core Ignition Wires.
# Bosch *9605 Double-Iridium Spark Plugs.
# Motorcraft *PW357 Water Pump.
# Motorcarft *RT1234 Thermostat.
# Motorcraft *YB541 Fan Clutch.
# Bosch *15717 Oxygen Sensors.(4)
# Bosch *SR7533N Starter.
# Bosch *AL7537N 130-Amp Alternator.
# Gates *K060980RPM RPM Series Serpentine Belt.
# Gates *38386 DriveAlign Belt Tensioner.
# Motorcraft *KM2973 Upper Radiator Hose.
# Motorcraft *KM2973 Lower Radiator Hose Assembly.
# Dorman *624-107 Electric Fan Assembly
# Motorcraft *YCC166 Air Conditioning Compressor
# Four Seasons *38904 Severe Service Orifice Tube
# Behr *351214031 PAO Compressor Oil
# Dual Exhaust - Walker *40383 H-pipe.
# MagnaFlow *18134 - 2" x 3.5" x 24" Glasspacks.
# Walker Tail Pipes - *46761(right side); *46789 (left side)
# Superior *28-6201 2 1/2" x 6" Stainless Steel, Slant-cut Exhaust Tips
# B&M *70268 13,000 b.t.u. Transmission Cooler.
# B&M *40264 Transmission Shift Improver Kit.
# B&M *80250 Transmission Drain Plug.
# XPERT Performance Cast Aluminum Differential Girdle.
# LubeLocker *LLR-F880 Differential Gasket
# Energy Suspension *4.3150G Urethane Control Arm Bushings (front, upper & lower)
# MOOG Greasable Ball Joints, Tie Rods, Idler Arm. (front)
# MOOG *K8853 Greaseable End Links (front).
# MOOG *513104 Wheel Bearing Hubs (front)
# ADDCO 1 1/4th" Front Anti-Sway Bar, with Energy Suspension Greasable Urethane Bushings.
# ADDCO 1" Rear Anti-Sway Bar, Urethane Bushings.
# Energy Suspension End Links with Urethane Bushings (rear).
Eclipse Brake Calipers (front & rear).
# ACDelco Drilled & Slotted Brake Rotors (front & rear).
# Motorcraft Police Brake Pads (front & rear).
# D.O.T. 4 Hi-Temp Brake Fluid.
# 98T Goodyear Assurance ComforTread Touring Tires.
5 "Italian Lace" 15" alloy wheels (includes spare).
# HELLA *980860801 Daytime Running Lights.
# Dorman *38445 Door Strikers
# Garmin *66LMT Navigation
Custom headliner by "Hot Rod Interiors", Glendale, AZ.
Dual exhaust fitted by "MufflerMasters", Avondale, AZ
** - All parts installed on this restoration are guaranteed to be GLUTEN-FREE.
*** - No animals were harmed during this restoration
Old 11-22-2017, 04:28 PM
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The clamp I am talking about goes from the snorkel to the throttle body it's about 4 inches in diameter but it really didn't make any difference since the connection was pretty tight to begin with - on another note do you know if the eatc units in the 95 Grand Marquis had screw in or soldered bulbs I'm trying to decide if I need to send my unit out it works but half the lights are off so annoying at night thanks
Old 11-22-2017, 04:31 PM
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One last thing I am trying to do is replace the rear view mirror with an auto dimming one sourced from a Lincoln or Mercury and I can feel a little plug up at the edge of the headliner do you have any idea if a replacement mirror with plug-in I see some harnesses for sale but I'm not getting into pulling the whole headliner for this project thanks
Old 11-23-2017, 09:54 AM
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Location: Phoenix, AZ., USA
Posts: 289
Default Bulbs and Mirror

The Factory Shop Manual shows a picture of your ATC unit is illuminated by a "VFD" (vacuum fluorescent display), and there is no reference to any "bulbs".
If you plan to keep the car, I suggest that you have the unit "rebuilt" at one of the shops that does that job. A rebuild should last for many years.
No help with the mirror -- can't find any reference to swapping them out.
Sorry about that. ;>(
Old 11-23-2017, 12:27 PM
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Thanks! There's a YouTube video out there of a guy rebuilding one and some of them had screw-in bulbs others were soldered on the circuit board but I won't know until I tear it apart I guess. I did reach out to some of the companies that rebuild these things so once they get back to me I guess we'll figure it out.
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