1998 mustang GT hesitation that I can't solve.

What have you done to rule out excessive EGR flow?

Have you verified that the charging voltage is stable? No ripple?

What is the fuel pressure when this problem occurs? Have you checked the voltage at the trunk mounted IFS switch when the problem occurs?

What is the MAF flow when this problem occurs.

Do the long term and short term fuel trims (LTFT STFT) change when this problem occurs?

What is the timing advance when this problem occurs?

Do you have an ODB2 scanner that is capable of monitoring Ford operational PID's? If you did this might make short work of this problem.

ForScan ODB2 scanner w ELM327 USB

Likely you can't find any specific solutions to this problem online because there are multiple "possible" causes. For the average DIY'er it can be a difficult nut to crack. Most people will "assume" that because a part has been replaced that this rules out it being a possible cause. They are further handicapped because they won't look at the role that dirty/loose/corroded sensor connectors might play. Same for dirty/loose/corroded grounds. Add to the mix the role that parts getting hot could play and this can quickly lead to a large number of "possible" causes.

Ford PATS does not disable the motor once started. However some aftermarket alarm systems do insert themselves within the ignition system.

BooStang89 said:

Fuel pressure normal at time of malfunction, charging system checked and rechecked also has a new alternator. I'll take the car out and hook up the scanner and check the timing advance when it does it. But I'm telling you it's not a thermal failure of a sensor. Because I can shut it off and instantly turn it back on and runs perfect for another 15-20 mins. Not the average joe either. Been building mustangs for 15 years and building mod motors for 13 years. Most likely if you can think of a test to do I've done it. I've checked all 5v reference and signal voltage on all sensors. I'll report back on the timing adv. I'm leaning on a bad pats module but I've never heard of one disabling an engine after its been started.

Click to expand...

GEM MODULE I BET

Try disabling the egr valve and driving the car to see if the problem continues. If the problem stops then you know the egr system is causing it. If the problem continues then that obviously isn't the issue.

The quick/easy way to disable EGR is by disconnecting and plugging the vacuum line to the EGR valve.

This method does have the downside that it won't catch a leaking EGR value. But one can rule this out by measuring the temperature of the EGR line down stream of the EGR valve. If there's an EGR flow then it has to be hotter downstream because of the EGR flow.

hey all first time poster here. I am having the same issue with my 98 GT. First project car ever and looking to help! I want to keep this thread ongoing i have scoured the internet for a solution. I have been going through the whole checklist.

Ny specifics is power loss. I bought the car used with an automatic transmission issue. I replaced the trans. And car drives and has power under light load. As soon as i go uphill or stomp to get on highway it bucks and loses power. If I shut the vehicle off and turn back on I will have normal power back until under load again.
I changed spark plugs, wires, coil pack, no change.

Cleaned the throttle body, and maf sensor no change.

I checked fuel pressure and turn key on without start, pressure will go to 36 psi. If I start the igniton pressure drops to 28 psi at idle. If I disconnect the vacuum line it shows 38 psi. Haynes manual shows I should be between 30 and 45 psi at idle, and between 40 and 50 psi with vac hose off. Also if given any throttle it drops slightly to about 36 and will only go as high as 33 psi with some revs.

I suspect it is fuel system since when I turn the car off and back on, the pump will repressure the lines and give me power until it struggles to keep up again. Bought a fuel filter and fuel pump and attacking those next. Will post results.

Other specifics about the car from previous owner is magnaflow cat back exhaust, and what appears to be an aftermarket upsized throttle body. Anyone know these upgrades would cause a lack in fuel? Maybe I should upgrade to high flow fuel pump?

Hopefully I can find what solves my issue and can help other forum users down the road!

just wanted to follow up. Probably in the wrong area but will help others with similar search results. 28 idle fuel pressure was way to low. Went in after fuel pump and fuel filter and found all kinds of junk that looked like sand in the pump bucket clogging up the pump and some nasty fuel. After I got it done today car rips again through all gears. I couldn't be happier. After replacing the pump fuel pressure is up at 50 engine idle. I hope this helps someone else with hesitation issues. Op sorry with all your troubles I have two 98 mustangs if I come across anything I will try to help.