Need help! Engine hesitating

[budbudford]

I have an 89 GT (5 spd manual) that is hesitating when I give it throttle at low rpms. For example, I am driving at 40mph in 4th gear and I floor it, the car sputters. If I drop it into a lower gear, the car accelerates fine. The hesitation only happens at lower rpms when I give it gas. It does not happen at idol or in neutral.

I have already replaced the TPS sensor, and I have no codes coming up? Any suggestions before I start throwing more parts at it? By the way, the mass air meter was replaced about 500 miles ago.

Thanks,
Ed

[bailey_57]

Ed just had the same type of thing happen to me on the way to the strip last week, replace your plug wires, cap and rotor. It help me out. Also if they are new then i would maybe check your base timing. If its stock look for it to be anywhere between 10 and 14 degrees advance.

When's the last time you changed your fuel filter? A clogged fuel filter can cause sputtering. You don't run platinum plugs, right? I've heard several people having sputtering/cutting out problems after switching to platinum plugs. Regular 'ol NGK or Autolite work best IMO.

[budbudford]

Originally Posted by Simi Stang

When's the last time you changed your fuel filter? A clogged fuel filter can cause sputtering. You don't run platinum plugs, right? I've heard several people having sputtering/cutting out problems after switching to platinum plugs. Regular 'ol NGK or Autolite work best IMO.

Nope, no platinum plugs, and fuel filter was changed last summer.

Well definitely change your fuel filter again then, if it's been that long. All it takes is one dirty tank of gas to get some debri in there. If that's not it...then I'd do all of the other tune up stuff (check your timing, new cap, rotor, plugs, wires...and go from there.

[bigdaddy999]

I would go with changing your plugs, and making sure they are gapped correctly, about .054". same thing happened to me, i went crazy changing everything, come to find out that the plugs were shot.

[budbudford]

Thanks for the replies. I ordered a tune-up "kit" from Summit yesterday. It will come with Motorsport wires, MSD cap, rotor, and coil. Bosch plugs.

I let you know what happens when I get these installed in the next day or two.

Ed

[budbudford]

Well after the tune up, everything works fine. New fuel filter from Napa, new Ford Racing wires, MSD cap, rotor and coil, and Splitfire plugs. Took it out on the freeway and problem solved! Back to 110mph in no time.

Thanks everyone!
Ed

[budbudford]

Ok... Now I am at my wits end!

I got in the car this morning to go to work, and after about 1 mile from the house, boom! The problem started all over again. Now I really don't know what to do.

While I was doing the tune-up, I checked the timing at the same time, and it was fine. The sputtering is back, and I am fuming!!!

Any other suggestions??? EGR valve???

[budbudford]

can anyone help?

[GhettoPop]

i've had a similiar problem for a few years now but mine only sputters when cold, once at 150 degreees and up, its fine. i changed the wires, plugs, cap, rotor, fuel filter as you did with no results. i'm interested in the replies you get from others.

could also be your ACT and/or ETC.
what is the voltage on your TPS sensor?

FYI i dont like the splitfire plugs. i think most people here would agree that autolites or motorcrafts are your best bet. cheap copper.

[87prjctpony]

my car use to do that... have you checked all the spark plugs??? or have you checked the sparkplug wires??? when i first got my car it came with mac headers( shaped really wierd) one of my plug boots were burnt and were passing current to the header. well this caused piston #7 not to work. just check those things.

[USMC302]

IMO, sounds like it's simply not enough timing. Some cars like more timing than others, what is your set at right now? Come up a couple at a time until you start pinging in the test run and back off one. Let us know.

[budbudford]

I'll re-check the plugs and wires to make sure there is proper contact since they were just replaced. As for the timing, I have adjusted it from 10 to 14 with no luck. I'm beginning to think it is the egr or maybe an o2 sensor, but there are no codes.

[USMC302]

Originally Posted by budbudford

As for the timing, I have adjusted it from 10 to 14 with no luck.

Was it pinging at 14 degrees? I have some friends running 16 and 17 degrees of timing just fine, keep going up until she starts pinging.

[budbudford]

Brought the timing up to 14 and heard a little pinging, then backed off.

I replaced the fuel pressure regulator, since a friend said to do that, but still no luck.

Any suggestions??

[HoodStrype]

Hey! Someone else with my problem... I've had this go on for two weeks!
Make sure you get plenty of vacuum to the fuel pressure regulator and turn it clockwise a half turn until it stops happening. This took me an hour and $10 in gas to fix... drive and pull over, drive and pull over.
Mine started when I added a 1" Spacer to the intake plenum. Have you done anything to increase your air intake?

[budbudford]

Thanks for your reply.

Turn the actual vacuum line a half turn? I was beginning to wonder if the problem was the vacuum line.

I do not have anything besides stock on the air intake except for a larger throttle body that I bought from Saleen a few years back.

I will do the carb cleaner test to check for leaks to the vacuum system today.

Is there any way that I can measure the pressure of the vacuum and know what it should be at?

I found this on ebay: http://cgi.ebay.com/ebaymotors/NOS-V...spagenameZWD1V

Thanks,
Ed

[HoodStrype]

If you haven't changed anything I'm starting to wonder. It sounds like you're not getting enough fuel under load. There is a place for a flat head screwdriver on the piece that holds the vacuum line on mine, it may not be stock. But it should not be just now having fuel problems if you haven't changed anything...
Now the vacuum just needs a good source, I would change that line or check it for a leak. When you pull it off the fpr does it stick to your finger, or slightly pull, or not at all? It should be noticable I think. My friend has very little vacuum and upped his fp. It was jerking a little and now it is perfect. As I was saying that was the problem on my car and we just fixed it. It was hesitating badly under alot of load... like 3rd and 4th gear at 1500 to 2200 rpm. Somtimes it took 5 or ten minutes to start, sometimes immediately. Mostly going up hills at low rpm.

[budbudford]

ok...

When I got home this evening I checked the vacuum pressure at the fuel pressure regulator, and there is plenty of suction there. I listened closely for any hissing on both ends of the tube and nothing. So far so good.

Now this is the frustrating part...

I decided to take it out for a 20 mile drive and check the hesitation under different load, rpm conditions. The car ran perfectly for 10 minutes then the hesitation came back. Not nearly as bad as it was before the FPR, but still there. It occured around 1500 - 2000 rpms in 2nd - 4th gear.

When I got back home I checked the vacuum again, and it was still fine. This time I checked the egr vacuum and the 2 others from that "tree" that you can pull apart. There is no air and or suction from that area or the egr valve. I am beginning to wonder if this is it.

Any ideas??

Thanks,
Ed