Hesitation and slight popping during acceleration? Why?

[MLMike25]

93 Notchback 5.0, AOD. No real mods (K/N, Flowmaster exhaust). Less than 49K original miles.



Let's say I'm in 1st or 2nd gear, accelerating normally, and then I floor it, I feel LOTS of hesitation and a pop or 2 (not a backfire) from the exhaust. It takes a few seconds before the car starts really responding (this does not happen in 3rd gear).



I thought it might be my injectors and I've been trying to clean them, but I think its probably something else 'cause it isn't getting any better (with Gumout fuel system cleaners).



What could it be?

[jimberg]

What's your timing set at? What kind of voltage are you reading off of your throttle position sensor? Do you have any vacuum leaks? How's your PCV valve? How's the idle? Does it start right up?

[MLMike25]

I spoke to my dad (lifelong mechanice by profession) and the first thing he said is to check the timing. I think the timing is set at 10 degrees, not 100% sure about that though.

I haven't checked the voltage and I'm not sure about the vacumn leaks. How would I check that. The car usually starts right up, but a few times I've noticed that it did not (thought it might be my starter).

Go easy on me, I'm a newbee and I don't live in the same state as my Dad so his over-the-phone help only goes so far so I'm sorta learning on my own. Thanks.

[bailey_57]

Have you ever touched the timing or the cap and rotor, maybe you have some plug wires in the wrong spot. Have you done anything lately that would have the PCV line off on the back of the engine. Last time I took my top end apart, I didn't hook up the PCV line and it made the same noise you described.

[fiveohpatrol]

to check for vacuum leaks, start by letting the car idle and listen for any hissing under the hood. If you can't hear anything, hook up a vacuum gauge to the tree over towards the drivers side of the firewall and see what it's got. A stocker should pull 14" or more at idle.

If you have a vacuum leak, this will allow unmetered air into the engine. The computer doesn't see this extra air and will not compensate with more fuel, which will result in a lean condition. The symptoms you described sound like a lean mixture (or timing, as mentioned above). So defeinately start checking around, because a majro lean condition can cause major problems.

Also, when checking your base timing, make sure you pull the spout connector (little black jumper plug up by the distributor, sorry if you already knew that)

good luck

[MLMike25]

Originally Posted by bailey_57

Have you ever touched the timing or the cap and rotor, maybe you have some plug wires in the wrong spot. Have you done anything lately that would have the PCV line off on the back of the engine. Last time I took my top end apart, I didn't hook up the PCV line and it made the same noise you described.

Yeah, a few weeks ago I tried to advance my timing, but I didn't actually go through with it b/c I was a little unsure.... so i don't think I actually changed anything. I'll double-check that and give an update.

thanks a lot guys.

[jimberg]

Before advancing your timing, make sure that you have 92 octane in your tank. You check your timing by warming up the engine to operating temp, then you remove the SPOUT connector. The SPOUT connector is a jumper that is on one of the wires that plugs into the TFI module which is mounted on the side of the distributor. Make sure it's set at 10. I wouldn't worry about advancing your timing until you get your other problem figured out.

When you floor it, is the hesitation immediate, or does it occur at a certain RPM? If it's immediate, I would definitely check the voltage between the green and black wires on your throttle position sensor. Use a digital voltmeter set so you can read a range of 0-6 volts or so. When the throttle is completely closed, you should read less than 1 volt. .85 to .95 should be good. If it's over, try loosening the screws on your TPS and see if you can turn it until it goes below 1 volt. If you can't do that, make sure it's installed correctly, or replace it. If you are getting below 1 volt, then move the throttle slowly and make sure the voltage smoothly increases beyond 4 volts. You want to make sure that there are no holes where the voltage suddenly drops. The computer uses the TPS to determine three states. Closed throttle (<1volt), part throttle ( >1v to <4.5v), and wide open throttle (>4.5v). If it doesn't detect these states properly, it may use the wrong amount of fuel or timing advance.

Does the starter crank when you have problems starting? If it does, you should probably check the PCV valve. It's tucked between the intake plenum and the firewall, so it's pretty hard to spot. It's pretty much plugs into the back and center of the lower intake manifold. There's also a filter that goes under it which can get gummed up. I would replace both the filter and the pcv valve. You need to pull the rubber grommet in order to pull the filter. The filter is pretty much like a coarse steel wool so to remove it, you just jam a needle nose pliers down there an pull it straight up. Be sure you have a replacement before you do this.

As far as vacuum leaks go, check the gasket between the upper and lower intake. When the engine is at idle, you can spray some carb/choke cleaner at suspect areas and see if it affects the idle.

[mustangII460]

TPS click here.

[jimdrechsler]

need more fuel is my guess. running lean? mine was doing that same popping and didnt find out until i hooked up similar to a dyno tune with things in my exhaust reading the air/fuel mixture. my fuel pressure gauge under my hood was broken and i didnt know it. adjusted the fuel pressure (along with burning a chip!) and runs much better. dropped more than .2 off ym 1/4 mile times!

[GhettoPop]

i have the same problem. when the car is cold and I put the engine under load, it will hesitate and the exhaust will pop. a second or two later the engine will respond normally. it happens in 1st, 2nd, and 3rd gear. it starts up fine, every once in a while it will want to stall out right after i start it. if i give it a little gas or start it again after it stalls once, it will idle fine. idle is good when cold and warm. once i drive for 5 min and car warms a little, no more problems. injectors, TPS, TB, etc are all stock with 130,000+ miles. the timing is at 14 and i run 87 octine gas as i get no pinging and i have been running good at that timing before this problem started. i dont think i have any vacuum leaks but will check with a gauge at the tree. i will also check the tps voltage and i already have a new pcv valve and screen to pop in. will post my results...........

how can i checl fuell pressure? is there any gain to buying an adjustable fuel regulator and adjusting fuel pressure on a stock engine?

[PKRWUD]

I'm gonna go out on a limb here. Next time you start it up, and it starts and idles nicely, disconnect and plug the vacuum hose going to the EGR valve, and see if that makes any difference with your problem. If it does, the valve may be sticking.