Hesitation when pressing the accelerator

racenmotorsports · Dec 2, 2011

Ok, I got this new to me mustang from a guy. It's a 95 but he replaced the engine with a 98 as the original needed head gaskets and he had the motor.

It hesitates, more like stumbles when I push the go pedal. The guy said it did it until it warmed up and then it would go away and after driving it, not so much.

I've researched it a lot on here, cleaned all the intake sensors. I checked and changed out the TPS since I bought a new one anyway, my fluke showed a dead spot around 3.xx volts up and down so it was worth the 20 bucks and piece of mind. I've cleaned the throttlebody out and did notice that the intake looked pretty dirty. The plug wires looked like they were orignial and had cuts in them, changed them and put the correct 605 plugs in. I checked the PCV valve as I noticed it was not sitting in the gromet correctly and now it's sitting in there good, not sure if it originally was plugged into the back side of the intake correctly or not, but it is now.

Anyway, after all of that, I expected it to start up and be decent at least, but no such luck, push the go pedal and nothing for 1-2 seconds then it goes. Not sure where to look now. I know the fuel looks and smells good, it was a daily driver for this guy. One other thing is that when it's revved up, say 2500-3000 I can see the engine looks like it has a slight miss or stumble, nothing I can hear just that every few seconds the engine will vibrate if that makes sense.

Any ideas where to look next. I sure was hoping it was the TPS.

96GT02 · Dec 2, 2011

Is your car an auto?

racenmotorsports · Dec 2, 2011

Nope 5 speed

LilRoush · Dec 3, 2011

I'd look at the injectors next based on the 'miss' you are having.

ttocs · Dec 3, 2011

vac leak?

g36 monkey · Dec 3, 2011

I would guess fuel delivery. If a vacuum leak was that bad I would imagine it would idle pretty rough.

Try running some injector cleaner to see if it helps at all.

Is it a dead spot at those rpms, like it will pick up afterward, or is it all the time just particularly bad at that engine speed.

Also does it do it while driving only or does it get rough if you just rev it.

Sorry for all the questions but I know it will help us answer it.

ttocs · Dec 3, 2011

could be fuel. I upgraded my pump recently and it did help the drivability of it, as well as in the higher rpms as well.

Slykin · Dec 3, 2011

Sounds just like when I forgot to plug in my MAF a couple weeks ago lol...

racenmotorsports · Dec 3, 2011

Thanks for the responses. Sorry it took so long to get back, I've been tearing the dirt track car down for the rebuild...

I don't think it's a vac leak, when I create one of those it runs like crap. I don't hear one and when I shot starting fluid in all the right areas I didn't get anything.
it only happens when you try to get on it. But always when you try to push it, only between say 750 and 1100. If I go slow, it's not so bad.

I'm starting to think fuel delivery too. Based on the plug wires, I imagine everything is bone stock and OLD now. It may be a fuel pump too, when it's up at the higher rpms it reminds me of the problems I had with my contour.

g36 monkey · Dec 3, 2011

I would guess fuel pump and injectors. I would upgrade it if I had to change it, but that's just me.

racenmotorsports · Dec 3, 2011

If I got to go that far, what do you suggest to upgrade with?

ttocs · Dec 3, 2011

you can doe a 255LPH fuel pump and get new injectors but if you get bigger ones you will need a tune.

Musturd · Dec 3, 2011

Timing

g36 monkey · Dec 4, 2011

255lph should be more than sufficient. 24 pound injectors would be fine too, unless you want boost later on.

robb15033 · Dec 5, 2011

I hope this doesn't come across as such a redundant statement or sound silly but I feel strongly about suggesting these easy items:
-Air leaks from CAI connections, egr, ect..
-Plugs. Wire boot connections, and ign. coil connections.
-Lastly, (Again, I know) Seafoam one full can in gas tank. One full can induced through vacuum line slowly until smoke clears.
-If I could, I would surely offer to do these checks for you myself, because it hits me as a gut feeling.
Summary- Fuel dilevery+spark is my guess!

racenmotorsports · Dec 5, 2011

I'm not sure the route I'm going to go, with injectors and all, it's going to be my daughter's car after all.

I'm pretty sure there aren't any air leaks and the plugs and wires are good, checked again. I'm going to get a tester and see if it's fuel delivery issue. I'm pretty sure now that it's a fuel thing either dirty clogged injectors, bad fuel pump or both. I plan on checking that this week. Hopefully I find it!

Mrstangerbanger · Dec 5, 2011

Also what computer does the car have?

Have you check the car with a diagnostic Machine like a snap on Mt2500? ( its a amazing machine i would see if someone can do a function test and see what happens )

How does the car run when you first start it in the morning ?

Post a video of what the car is doing to give more info thank

racenmotorsports · Dec 11, 2011

ok, I haven't made a video yet. Today I checked the the fuel pressure it's about 30# at idle when I move the throttle it goes up to about 40ish# and then comes back down. Strange thing is that it doesn't hold any readable pressure after I turn the car off. I also put the reader to it, but it wouldn't connect to the computer for some reason. It's definately and OBDII system under the dash, none of the OBDI connectors are in the engine compartment. Check engine is not one anyway.
I can't get the car to my buddy's shop til next week (I haven't put plates or insurance) on it yet so I don't feel comfortable to drive it the 5 miles to his shop. He's got all the extra testing equipment (noid lights and such) and the real deal fuel injector cleaing system that I can use.

Better than everything else, when I changed the fuel filter today, I found out there aren't any brake lines in the rear (something I didn't notice before) and I don't think the PO even knew about it.

g36 monkey · Dec 11, 2011

Being a 95 its OBDI which is probably why that computer didn't pick it up.

racenmotorsports · Dec 12, 2011

I thought the same thing with it, but doing a lot of research (here mostly) the v-6 95's were OBD-II and there aren't any OBD-I connections. I'll get the hesitation fixed, it's something fuel related I'm sure, but it runs, not great, but it runs. My bigger concern now is the brake system. I hate brakes and having to re-do them is going to drive me nuts.