Engine stumbles and misses under normal acceleration

nick6690 · Jun 27, 2010

This used to happen only when it was cold but it's getting worse and it does it all the time now. When accelerating from a stop it misses and stumbles around 2000-2500 mainly in 2nd, 3rd, and 4th gear. Anyone know what could be the problem? I appreciate any help.

Kdubslugga · Jun 27, 2010

What kind of mass air are you running??? Does it do it only when cold, does it go away at all when warm, does it hesitate at all when you floor it from a stop???

nick6690 · Jun 27, 2010

I looked up the part number off the MAF and its off a 93 cobra r, which is kinda weird but i guess thats what it is. I tried cleaning it and it helped a little at first but it came back.

The throttle response is perfect. It used to do it when it was cold but it went away and now it does it all the time.

Oh and i pulled the codes and its clean.

nick6690 · Jun 27, 2010

Oh and another thing, it's been sucking down a ton of gas.

Kdubslugga · Jun 27, 2010

Do you have any idea what your fuel pressure is?? What happens if you try and drive through the missing and stumbling? What I mean is, when it starts to miss or stumble and you leave a light foot on the throttle what happens?? Will it stall out? Best thing to start with is pull a spark plug. Does it stumble in Neutral if you bring the Rpms up to 2500?

nick6690 · Jun 27, 2010

Its around 40 psi and my tuner set the timing at 10 degrees.
I try to have a light foot when its cold out or it will start doing it. The more gas you give it the more it does it and it starts popping through the intake until around 2800 then it clears up.

Its not as bad when its warm as it is when its cold.
And it doesnt do it when in neutral, only during acceleration.

k4mjk · Jun 27, 2010

exhaust leak was causing mine to act weird

jrichker · Jun 28, 2010

No codes? Did you get the computer internal check OK code 11 (two single flashes in quick succession)?

nick6690 · Jun 28, 2010

Ok i tried it again and with the KOEO test i got 67 and 84.

As for the 84 code, i put plugs in the back of the heads and the smog pump is removed.

KOER i got an 11

nick6690 · Jun 28, 2010

k4mjk said:
exhaust leak was causing mine to act weird

was your car acting similar to mine?

Haus · Jun 28, 2010

If you have a analog volt meter, maybe you can test the TPS and see if it has a clean sweep as the throttle is pressed. make sure there is no dead spots in the TPS

Haus · Jun 28, 2010

And how long have you had the air pump removed with your pypes Catted X pipe??

I personally would put your smog pump back on or get an off road mid pipe

This could be your problem. When you have Converters you need that extra air from the Smog pump for the cats to work properly. If not they could clog and cause the problem you are having

nick6690 · Jun 28, 2010

Sorry man, I haven't updated my sig.
I now have Mac longtubes and a VRS o/r x pipe.

Ill try the TPS and see what happens.

Thanks for everyones help.

nickmav70 · Jun 28, 2010

did you pull the plugs? it sounds to me like fouled plugs... exactly what mine did every three weeks when i had oil fouled plugs from my cobra intake

jrichker · Jun 28, 2010

Code 67 - clutch not depressed (5 speed) or car not in neutral or park (auto) or A/C in On position when codes where dumped. Possible neutral safety switch or wiring problem. This code may prevent you from running the Key On Engine On tests. You can generally ignore this code, since it has no effect on engine performance.

The computer wants to make sure the A/C is off due to the added load on the engine for the engine running tests. It also checks to see that the transmission is in Neutral or the clutch depressed (T5, T56, Tremec 3550 & TKO). This prevents the diagnostics from being run when the car is driven. Key On Engine Running test mode takes the throttle control away from the driver for several tests. This could prove hazardous if the computer was jumpered into test mode and then driven.

The NSS code 67 can be bypassed for testing. You will need to temporarily ground computer pin 30 to the chassis. Computer pin 30 uses a Lt blue/yellow wire. Remove the passenger side kick panel and then remove the plastic cover from the computer wiring connector. Use a safety pin to probe the connector from the rear. Jumper the safety pin to the ground near the computer.

Code 84 EGR Vacuum Regulator failure – Broken vacuum lines, no +12 volts, regulator coil open circuit. The EVR regulates vacuum to the EGR valve to maintain the correct amount of vacuum. The solenoid coil should measure 20-70 Ohms resistance. The regulator has a vacuum feed on the bottom which draws from the intake manifold. The other vacuum line is regulated vacuum going to the EGR valve. One side of the EVR electrical circuit is +12 volts anytime the ignition switch is in the run position. The other side of the electrical circuit is the ground path and is controlled by the computer. The computer switches the ground on and off to control the regulator solenoid.

nick6690 · Jun 28, 2010

I forgot about having to push the clutch in when dumping codes so that explain code 67.

Im gonna try putting a set of plugs in as well and see what that does. Theyve been in for about a year and a half and I have had an issue with oil coming up through the pcv so that might explain it. Ive recently bought a different set of valve covers and Im using a different pcv setup, that seems to have fixed it that problem.

nick6690 · Jun 29, 2010

I checked the plugs and they look good.

I put a voltmeter on the TPS and the voltage is good but there is a dead spot where the screen on the voltmeter goes blank. I ordered a new TPS and I'm gonna pick it up in the morning and see if that fixes it, which im 99% sure it will.

nick6690 · Jun 30, 2010

Well the new TPS didn't fix it. Any other ideas as to what it is?

jrichker · Jun 30, 2010

I'm not quite sure about what I see in your engine photo, but it looks like you have a cone filter in the engine compartment. That's a big no-no, since the wash of hot air from the engine and fan upsets the airflow through the MAF.

Keep in mind that MSD stands for "May Suddenly Die", and all MSD parts seem to suffer from quality control problems.

Put the stock ignition and distributor back on the engine and fix the air intake so that it picks up inside the fender well. The stock airbox and filter will beat most of the Cold Air Intake kits you can buy, and it is a lot cheaper.

nick6690 · Jul 1, 2010

Well it is the stock distributor, it just has a MSD cap, it was on there when I bought the car.

I'm gonna try to find another stock distributor and see if it makes a difference.

And I'm going to look into getting a Anderson Power Pipe.

Engine stumbles and misses under normal acceleration

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