Hesitation during acceleration

CobraBill96 · Jul 25, 2005

Need some suggestions. Have a 1996 Cobra with 80,000 miles. I have had it about 4 months now and everything has been fine with it. I recently had the engine flushed, oil changed, tranny fluid changed and put some fuel system cleaner in with a fresh tank of gas. Last week, just before the end of the tank, I felt the engine hesitating during mild acceleration and it is still doing it after filling the tank with gas again. I am going to change the plugs since they need to be done anyway, but I am wondering if this is an electrical or a fuel distribution problem. I am not getting any 'check engine' lights.

Any thoughts? Thanks.

COBRA90GT · Jul 25, 2005

While you are checking/replacing the plugs, it won't hurt to change the fuel filter either. At what RPM is the engine hesitating? You are using premium gas, correct?

CobraBill96 · Jul 25, 2005

Cobra90GT: It happens mostly between 1200 and 3500 RPM. However, if I gradually accelerate I am ok. If I hit the gas in any gear and I am in that RPM range it hesitates badly and repeatedly.

I am using 93 octane.

coolguy10786 · Jul 25, 2005

My 96 cobra did that to not nearly as bad anymore, i changed the plugs and fuel filter which helped barely, used seafoam and cleaned MAF at same time and helped majorly. I say clean the MAF sensor especially if you have a K&N filter because if its over oiled the it gets on the MAF. I know cause i did it. Clean the MAF with a can of electric parts cleaner comes in red and black aersol can. hope it helps

CobraBill96 · Jul 26, 2005

Changed the fuel filter last night. No change. I don't have a K&N on it yet, bu that will go on this week. Plugs are next. Going to try and get that done tonight. I'll let you guys know.

COBRA COUPE · Jul 26, 2005

I bet your IMRC's & secondary's need cleaned.

CobraBill96 · Jul 27, 2005

Cobra Coupe: Know of any good ways to do that without yanking the engine apart?

CobraBill96

COBRA COUPE · Jul 27, 2005

CobraBill96 said:
Cobra Coupe: Know of any good ways to do that without yanking the engine apart?

CobraBill96

No, They must be pulled but its well worth it if your car has alot of miles on it, I noticed a huge diffrence from cleaning them an the secodarys. Its a good idea to replace the Actuator box to..

Heres a good write up on http://home.flash.net/~ivc1/cobra/imrc.html

One thing I did thou is when you clean your secondarys use a shop vac to suck out the carb cleaner.

cold96snake · Jul 27, 2005

CobraBill96 said:
Cobra Coupe: Know of any good ways to do that without yanking the engine apart?

CobraBill96

When you floor it, which you should do because its'a cobra, you'll feel a bump @ 3500rpm's. (actually 3250, but if you have 4.10's....)

69 Rustang · Aug 1, 2005

Check your fuel pressure. I had an 86 GT that did the exact same thing--right after filling up it started to hesitate and stumble. Accelleration was on pace with a AMC Gremlin. After changing the fuel filter myself, taking it to the dealer and paying them to clean my injectors, taking it back and them telling me I needed a new fuel pump I got mad--told them to replace the pump but if it didn't fix it the pump and fuel injector cleaning would be free. They decided to look at the car again and called me back and said the fuel pressure regulator was bad. I told them same deal (free if they are wrong)--they replaced it and the car ran the best it had ever run since new. The regulator is easy to change--on the passenger side at the back of the fuel rail. Get someone with a fuel injection test kit and hook up on the front right side rail fitting to test the pressure. Start the engine, rev it, consider even snaking the gauge out and taping it to the wipers so you can drive it for real world testing. Before tearing into the engine or changing more parts I would start with testing fuel pressure.

CobraBill96 · Aug 3, 2005

OK. Well I changed the plugs, cleaned the MAF sensor and put in a K&N. It definitely is better but not completely fixed. The tank of gas I have in right now has Seafoam added so we'll see what happens. I have a question though. I have seen posts that say the IMRC's open at about 3300 RPM and that they are probably part of the problem, if not the cause. So, while I am seriously considering pulling them and cleaning them I need to know if the IMRC's can affect things in the 1200 to 2500 RPM range. That is when I still feel the hesitation. Especially if I am on the highway in 5th and hit the gas.

Any thoughts or suggestions.

CobraBill96

COBRA COUPE · Aug 4, 2005

CobraBill96 said:
OK. Well I changed the plugs, cleaned the MAF sensor and put in a K&N. It definitely is better but not completely fixed. The tank of gas I have in right now has Seafoam added so we'll see what happens. I have a question though. I have seen posts that say the IMRC's open at about 3300 RPM and that they are probably part of the problem, if not the cause. So, while I am seriously considering pulling them and cleaning them I need to know if the IMRC's can affect things in the 1200 to 2500 RPM range. That is when I still feel the hesitation. Especially if I am on the highway in 5th and hit the gas.

Any thoughts or suggestions.

CobraBill96

Its possible if there stuck open you would feel a low end torque loss also either way its not to bad of a job to clean them an make sure you clean the secondarys mine were beyond nasty an is where most of the power loss comes from as no fuel goes to them to clean them.. Goodluck man

MangledAxle · Aug 4, 2005

have you replace the spark plug wires? don't ignore them

CobraBill96 · Aug 9, 2005

Haven't replaced the spark plugs wires... yet. The engine has gotten better in the past couple of days, bad gas / plugged injector maybe. If it continues I am definitely going to change the wires. Needs to be done anyway.

CobraBill96 · Aug 16, 2005

Plug wires fixed it.

COBRA90GT · Aug 16, 2005

CobraBill96 said:
Plug wires fixed it.

Good to hear it was a simple fix.

Hesitation during acceleration

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