Surge/hesitation After Plugs

Dacon · Aug 22, 2014

I just did the plugs and wires on my 94, and wow, they were old and in there -good- (and came out near .07 gaps).

Wasn't running great when I started it, so killed it and found 3 wires weren't fully seated. Firmed them up, and it idles/runs good. But now @ around 2700rpm, it starts to bog/sputter/surge and won't rev any higher. I tossed a new coil pack on it, it made it sputter more frequently, and surge off idle when you give it gas. Put stock coil pack back in, surge off idle dissapears and it has a the struggle/miss around 2700rpm. After it warms up a bit, it wants to act a little more erratic on the throttle as well.

Only thing changed were plugs and wires, all are in the right order (it runs smooth under 2500rpm, and is very smooth until it's @ full running temperature) and were gapped to .054... any thoughts ?

Dacon · Aug 22, 2014

Also, when I removed the intake elbow to do passenger side and put it back on, I had to man handle it back on, any chance it might have broken my MAF sensor and started causing this ? My hands are bloody and bruised from trying to make sure the plug wires cant get on any more.

Dacon · Aug 22, 2014

I wish I could delete my own threads... forgot I dropped a freshly oiled k&n filter in it. It's was a dirty MAF

madspeed · Aug 24, 2014

live and learn!

Dacon · Aug 25, 2014

Well I was wrong, cleaning the MAF sensor did nothing.

Car runs great when cold/warming up. Once it gets fully warmed, it will start hesitating/misfiring around 3k. Then will do it less commonly around 1500rpm. I thought maybe Torque Converter shudder, but it does it when dragging the brakes and near 3k is accompanied by the classic marble in a paint can sound.

So, my new plugs (NGK, ~250km on them) are coming out tomorrow, and new Autolite 25's are going in. Any other ideas/tips before I give up and pay someone ? Only put in new plugs, wires, and a coil pack (removed the coil pack for now, seems to amplify problems). Should I be looking at a new distributor ?

Hahaha, this is what I get for not taking mechanics in high school.

toyman · Aug 25, 2014

May be fuel related. Test pressure with a gauge if possible at the schrader valve on the fuel rail. Look for fuel being present when you remove the vacuum line to the fuel pressure regulator (FPR). Also consider changing the fuel filter. It may be the oem piece. Clean the MAF element if you haven't done so already. These are minimal cost maintenance items.

ronstang94 · Aug 26, 2014

Sounds similar to a problem that I was having. I was much younger then and didn't know that much about cars yet. I gave up and took it to a shop. They had a very hard time finding the problem, even with all of their fancy machines. $500 and a new MAF later, the problem was solved.

Try to find someone willing to let you try on their MAF. There are a lot of cars that use the same part.

Dacon · Aug 28, 2014

New fuel filter, new tfi/ignition controller and MAF today(both for $80, couldn't say no)...

So i figured while my intake elbow was off to do MAF i'd change out my plugs. Drivers were easy, passenger Cylinder 2/3 was easy... cylinder 1 ate the inside of my plug wire. It has the metal connection wrapped around the electrode and the plug boot is now fully separate/empty, it slimed off as well like the boot was melted slightly inside. So I ordered new MSD wires, get them tomorrow and I have to try to pull off this boot connector off the spark plug. It is now long enough my plug socket cant make connection, lol. Always something with this guy!

ronstang94 · Aug 29, 2014

All that for $80? And it was all new?

Dacon · Aug 29, 2014

ronstang94 said:
All that for $80? And it was all new?

The ignition controller was new in store, MAF was new stolen off a buddy who bought it just before getting an aftermarket MAF so his stock one was still NIB and became mine. I'm sure that'll haunt me in the future. Just got my new MSD wires, look shorter than stock/aftermarket ones I have now, but I'm betting it's a tomorrow morning kind of job lol.

ronstang94 · Aug 29, 2014

Nice!

Dacon · Aug 30, 2014

Well, new auto lite 25s are in, MSD wires, MSD coil. No change.

Tested battery, was very low, replaced with a new one. Much smoother idle when warm, but the stutter/bucking persists when warm. Although it is more driveable/the stutter is more predictable (with the new battery). Also tested with the timing spout (? beside airbbox) disconnected as recommended by a mechanical friend, no change just higher rpms/less engine braking.

Still thinking spark is just not getting there as more/stronger spark (battery, plugs, coil) has smoothed out the idle at warm (for the most part) but kept up problems when more spark is required. New distributor rotor/cap lined for up for tomorrow, distributor if that fails. This is turning out to be a pricey plug job!

Dacon · Aug 31, 2014

Jesus, it never ends!

New rotor and cap, and the problem persists. But now along with a slightly off idle, rpms dropping when slowing down (only slowing down, not pumping the brake) the hesitation/bucking has moved to ~2000rpm, and it just shut itself off while parking (in reverse) today after testing. Noticed a slight squeal/chirp when I shut it off that wasn't there before this bs.

New distributor after the long weekend, probably just give it to a mechanic to fix, it has beaten me.

madspeed · Aug 31, 2014

Codes??

Dacon · Aug 31, 2014

KOEO = 1 1 1, pass.

KOER isn't giving codes (not even an 1-1-1), same procedure as KOEO, engine revs to ~1500, drops to below idle (almost stalling) then just idles. Left it for 3 minutes.

Slight noise (similar to lifters I think) coming from my distributor too, almost a knock/tick but didn't seem to get stronger with the KOER raising idle. Also very close to the top end so hard to tell if dist. or not.

WhiteCobra95 · Sep 2, 2014

With the cap off is there any play in the trigger wheel? For example, if you grab the trigger wheel and try to rotate it back in forth is there any movement? If that checks out, is the pickup sensor mounted solid to the distributor? Have you checked the timing at idle with the SPOUT unplugged - is the timing solid around 10° or your normal setpoint?

I had a problem with an old Duraspark distributor where the pickup came loose, sheared the index pin for the trigger wheel, but kept working at low speeds. I could set the base timing without problems but whenever I went WOT it would fall on it's face and miss. After checking a million other things, I finally grabbed the trigger wheel and it had about 30° of play in it. I think it was fine at idle, but with some rpms it would rotate back like huge spark retard. I know it's different with a mechanical distributor, but maybe something similar has happened with your TFI distributor.

In any case, trying another distributor sounds like a good plan. There are a lot of posts on here about the TFI pickups going bad, and usually rpms make the situation worse with a failure like that. Good luck!

Dacon · Sep 5, 2014

I gave up, gave it to a shop, damn good guys helping me sort through it too. Here's what they've told me, perhaps one of you guys can help unravel this mystery/give me something to help them out.

It's a fuel pressure issue, psi was very low and jumpy. Got a new pump, got the pressure within spec, but is still fluctuating, fluctuating is causing the hesitation. FPR is good, put in another to test. PSI runs high (80 or 90+ if I remember right) with fpr disconnected. Fuel lines have been disconnected and blown through, new fuel filter. All voltages, ground to pump check out, good voltages. No codes KOEO KOER or passive stored.

Going to try another fuel pump next week (I may go buy a walbro 255 as it's planned for spring anyways) on the off chance the new pump might be bad. Driveability is bad though, rough idle/hesitation from cold till warm now, hesitation is happening very low in the revs.

Any ideas or thoughts ? I miss when I thought cleaning my MAF fixed this, haha.

Chythar · Sep 6, 2014

Have the shop check voltage to the fuel pump. The relay for the fuel pump could be failing.

Dacon · Sep 6, 2014

The shop said the voltages running to the pump were all in spec (even when fluctuating), making him think the pump might be defective from the get go (was swapped 3 days ago). Could a faulty ECM/PCM/whatever you call this computer cause a fuel pressure surge/hesitation or would that be noticeable in voltage drops/rises at the pump?? Or would a lame PCM send a code?

Went to get groceries (stang is my only ride) and I got a block before going home. The thing acts like it has a gigantic lumpy cam in it. The problem has degraded from 'hesitation when getting on it' to 'hesitation/bucking 24/7, near undriveable'. Even at idle now it's sounding cammed, now I'm hoping I can make the 2km trip to the shop this week and have it sorted, lol.

Really dissuading me from wanting to get power out of this car, maybe a s197 would be a better call being 10 years newer, but it would eat all my build monies

Chythar · Sep 7, 2014

Our fuel systems are a return-style, which means the fuel pump is supposed to run at a consistent rate. Any fuel not used is returned to the tank. Voltage to the pump should not fluctuate. It's possible the CCRM at the front of the engine is going bad; it essentially controls voltage to the fuel pump, the engine and the fan. Do you have any other Mustang GT owners in your area? The CCRM is pretty expensive, and it would be easier to borrow one as a test.

Surge/hesitation After Plugs

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