Hesitation than cleared itself

[Vette73]

Like the title says hesitate than clear..

Have not driven my Z since Carlisle..Took it out this morning....Car ran fine for first five -six minutes.....Upon acceleration it began to hesitate than it would clear itself.....Did it about five or six times....Had car out for about 25 minutes...

Idle would also drop at times when I was stopped....Car is ported and cammed 91...

Accel injectors..Swapped out fuel filter about 7,000 miles ago....

Thought maybe its bad gas but I filled up the w end of carlisle....Car runs great up until this morning...

Thoughts?

[QB93Z]

Are you referring to hard acceleration (secondaries opening) or just mild acceleration in traffic?

Do you have access to a Tech 1 or similar scanner?


Jim

[Vette73]

Hey Jim..

Secondaries deleted..I would say normal acceleration....Roughness at idle at times as well...

[jss06c6]

Definitely sounds like a fueling issue. Did it stop after it was completely warmed up? Can you check fuel pressure upon acceleration? Are you still running with the original fuel pumps?

How long since Carlisle (I should know this)?

Steve

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[Vette73]

Hey Jim...

It performed the way its supposed to when it got fully warmed up....That's my next step, check the fuel pressure..Don't know if they are original fuel pumps...

Will take it to my mechanic maybe Saturday morning....Before this morning, last time I used car was the Sunday of carlisle weekend..

[jss06c6]

Hey Jim...

It performed the way its supposed to when it got fully warmed up....That's my next step, check the fuel pressure..Don't know if they are original fuel pumps...

Will take it to my mechanic maybe Saturday morning....Before this morning, last time I used car was the Sunday of carlisle weekend..Hmm, you might also pull your plugs and check them over.. pictures of them would be good as well..

Steve

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[XfireZ51]

Hey Jim...

It performed the way its supposed to when it got fully warmed up....That's my next step, check the fuel pressure..Don't know if they are original fuel pumps...

Will take it to my mechanic maybe Saturday morning....Before this morning, last time I used car was the Sunday of carlisle weekend..

Are you saying the issue was with “the warmup routine” as opposed to normal operation?

[Vette73]

Even if its not fully warmed up it should not have done this.....The last few mins of my drive it seemed to have gone away until I was backing into my garage I felt the idle start getting rough again...

Will see if my mechanic is in a " good mood " Saturday morning.....Will check for fueling issue..

[XfireZ51]

Even if its not fully warmed up it should not have done this.....The last few mins of my drive it seemed to have gone away until I was backing into my garage I felt the idle start getting rough again...

Will see if my mechanic is in a " good mood " Saturday morning.....Will check for fueling issue..

Trying to understand what conditions were different today from Carlisle, ie temperature, weather?

[Vette73]

Well it was cooler today.than Carlisle at least 25 degrees...Great driving weather though..Good air no humidity..

[G8nightman]

Might be a bad O2 but that will throw a code check engine light come on at all?


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[XfireZ51]

Well it was cooler today.than Carlisle at least 25 degrees...Great driving weather though..Good air no humidity..

Where is your MAT located?

[Vette73]

George....No code ...Had a bad one last year and swapped out..

[George Maz]

Fully warmed up, turn on headlamps, come to a stop and wait to see if idle will slow and SES light illuminates. Also can implement additional load of the Air Conditioning running (blower motor max setting 10). If it acts like it wants to stall, you probably have my custom tune installed on your car...lol.

I've become immune to this occasional condition due to being slightly lean at idle...no big deal.

[XfireZ51]

Fully warmed up, turn on headlamps, come to a stop and wait to see if idle will slow and SES light illuminates. Also can implement additional load of the Air Conditioning running (blower motor max setting 10). If it acts like it wants to stall, you probably have my custom tune installed on your car...lol.

I've become immune to this occasional condition due to being slightly lean at idle...no big deal.

George,

His car is a 91 so ur tune wouldn’t work unless someone “translated” it for a 91.

[mike100]

I had encountered poor driveability when the weather changed and I was still on winter blend calif gas when we had an 80 degree warm spell in February. Run through a tank before you spend any money

[Paul Workman]

I agree that fueling may be @ issue. Scanning the ALDL port will give you a pretty good idea how it is running. (O2s don't always throw a code - at least not right away. They can be failing or getting weak long before failing completely to cause a code (I've found).

Besides O2 function, you will be able to get a dynamic evaluation of ALL the sensors: a good place to start!:thumbsup:

I don't want to start speculating until we see what the scanner says first. JMO.

[Vette73]

Thanks guys....Not too familiar with scanners and such.....Will run this by my guy tommorow or the following week....Will keep everyone posted on the outcome..Which in turn may help fellow members,if such a problem arises with others...

[XfireZ51]

Was ur MAT sensor relocated?

[George Maz]

John, I have Vetronics Tech1A scanner with master cartridge updated...and extra O2 sensors.
Let me know if I can be of assistance to you.

[Vette73]

Took the car out again tonight...I'm reading that the car runs off the primary fuel pump once the temp reaches 176 degrees...

After about ten mins or so the symptoms started again.....Very rough running till I hit about 3,000 rpm than it would jump...

Im thinking maybe the primary pump is going.......What's the easiest way to check this? If it is , don't the Z use the same pump from a 96 Chevy suburban?

[GOLDCYLON]

Was ur MAT sensor relocated?





Ahem Dom is on point did you relocate the sensor? Are you thinking open loop close loop Dom

[Vette73]

Yes....MAT sensor is relocated to the lower front part of car......

????

[Vette73]

I would take a photo of relocation but I never seem to be able to load a photo on this site..

[XfireZ51]

I would take a photo of relocation but I never seem to be able to load a photo on this site..

Relocating the MAT to the front without making corresponding changes to the calibration will cause fueling issues. The MAT table values assume that the incoming air will be at about the same temp as the coolant(~ 80C). However, moving the sensor to the front, the ECM never “sees” that temp. It always thinks its colder than it is. It may have run ok when temps were warmer perhaps because it was tuned w that “temp” and the VE table basically compensate somewhat for that. But once the intake air temp drops and gets cooler, the ECM can’t correct enough. The intent of the MAT/INT sensors is to modify fueling based on intake air temp so as the air temp rises and falls, the ECM changes Pulse Width to compensate thus maintaining a consistent fueling. The cooler the air, the more fuel due to air density. That’s why the motor changes the way it is running while sitting at idle, because intake air temp changes. With unmodified MAT table values, the ECM is doing one thing while it should be doing something else.

[Vette73]

Not too familiar with this...Only thing I can say is, I relocated this about 3 years ago and use my car all year round..

Dempsey gave it the Dragon heart package w cams last December...When I picked up the car temps were in the 40's and it has run fine up until like I said a few days ago..

[XfireZ51]

Not too familiar with this...Only thing I can say is, I relocated this about 3 years ago and use my car all year round..

Dempsey gave it the Dragon heart package w cams last December...When I picked up the car temps were in the 40's and it has run fine up until like I said a few days ago..

Well u r providing new information. May very well be a pump issue.

[Vette73]

X-FIRE Thnx for looking out..Will be travelling for a week..When I get back will check the pumps...

[RichS]

It's easy enough to check the pumps and pressure using the tips from this site. You need a volt meter and a pressure gage. My pumps tested good but I replaced them because I figured they were 23 years old, and had Phil do a regulator for me to since mine seemed to stick once after sitting over the winter. Very easy to replace the pumps if needed.