: Horrible Engine Bucking 93 N* Allante



Edahall
07-20-09, 10:06 PM
While on a trip driving towards San Diego, my 93 Allante suddenly started bucking as though the gas tank was running empty on fuel. I still had nearly 1/2 a tank of fuel. I managed to get the car off the freeway and to a gas station. I thought it might be a ground issue so I got a piece of wire and clamped one side down to the engine and the other side to the shock tower. However, it made no difference. I decided to take the chance and continued on my trip. After several miles, the bucking seemed to clear up. About 2 hours from San Diego, I got hungry and parked the car so I could eat. About 1/2 hour, I returned and started the car and the problem was even worse. It took me about 15 tries to get engine to run. I finally got the engine started, put it into gear and smashed the throttle to the floor to get the car rolling. Once I got back to the freeway, the engines horrible bucking slowly cleared up. I made it to my destination in San Diego but who knows if I'm going to be able to drive it tomorrow.

From previous posts, I have not been able to fix the warm hard starting problem. Gas mileage around town is also horrible and much worse than my 82 Chevy Suburban. I have replaced the FPR, spark plug wires and fuel filter. I don't believe the problem is the Idle Speed Controller. I thought that was the problem at first and disconnected it but it continued to buck in idle. Basically, it idles from 500 rpm's to about 2000 rpm's. The engine keeps dying and does not want to start back up again. The DIC is reporting no codes.

Ranger
07-20-09, 11:55 PM
I'd get a fuel pressure reading. Might be a weak fuel pump.

Edahall
07-21-09, 12:29 AM
I'd get a fuel pressure reading. Might be a weak fuel pump.

The fuel pressure is 40 psi at idle. Spec is 42 psi so it's -2 psi off. Hmm.

Edahall
07-21-09, 01:12 AM
Update:

The following codes are present as history:
P032 ..... Open MAP Sensor Signal
P041 ..... No Cam Reference Signal from Ignition Control Module
P071 ..... Intermittent MAP Signal
P095 ..... Engine Stall Detected

The way the engine runs is if someone is turning the ignition on and off at a frequency of 1 second.

Ranger
07-21-09, 01:34 AM
:hmm: Hard to say based on those codes if it is the ICM or the MAP sensor. I don't know enough about either to say which could cause that type of problem. Then again, maybe it's both.

Edahall
07-24-09, 01:10 PM
UPDATE:

Thanks for all the help. Turns out, the problem was most likely was the Manifold Absolute Pressure (MAP) sensor. I drove the car back home on the 200 mile trip without incident last night. I was lucky that this was the problem because it was a relatively easy sensor to change out and I was able to do it in the hotel parking lot.

The problem with the bucking came on suddenly so I figured most likely it had something to do with the computer rather than clogged injectors or CAT. The engine was also not missing so that ruled out fuel problems, spark problems or EGR problems. I have already put in new coils, new custom made MSD wires and a new AC Delco FPR. So it came down to a bad Crankshaft Position Sensor (CPS), bad MAP sensor, bad PCM or bad ground. I ruled out that it was a bad ground by using my battery jumper and connecting one end to the engine block and the other to the negative battery terminal wire. This made no change so I knew that this was not the problem.

This new MAP sensor however has not fixed the previous hard warm starting problems and bad city economy. It still takes lots of cranking to get the car started and once started, I can smell raw fuel out the exhaust. I also notice that when driving on the freeway going downhill, the engine does a slight amount of surging at minimal throttle level. I have not put in new spark plugs so I’m going to try that next.

Submariner409
07-24-09, 08:19 PM
One or more fuel injectors is stuck open or sticky. The injector coil should read about 12 - 14 Ohms.

Hard start and fuel smell is rich mixture, and you've checked the FPR and line pressure.

Either check the injectors or get a rebuilt set from www.rockauto.com. (Replacing 1 or 2 injectors is cheaper, but then the new(er) one(s) have a different flow rate than the remaining units.)

Is this a Northstar or a throttlebody injected engine ????

Edahall
07-25-09, 02:26 AM
One or more fuel injectors is stuck open or sticky. The injector coil should read about 12 - 14 Ohms.

Hard start and fuel smell is rich mixture, and you've checked the FPR and line pressure.

Either check the injectors or get a rebuilt set from www.rockauto.com (http://www.rockauto.com). (Replacing 1 or 2 injectors is cheaper, but then the new(er) one(s) have a different flow rate than the remaining units.)

Is this a Northstar or a throttlebody injected engine ????

This car has the 32 Valve Northstar engine and was the only year Allante to have this engine. I replaced the FPR with a new AC Delco but it didn't seem to make any difference. I did a fuel pressure test and it read 40 psi which is 2 off from the spec of 42 psi. The fuel pressure does not drop off so I don't believe the injectors are leaking. I'll use a meter and test the ohms on each injectors coil and reply back.

askimbenim
07-27-09, 01:46 AM
Please check the battery voltage. Bat voltage and fuel pump folw are connected,
higher voltage => higher fuel flow => higher pressure after regulator

and opposite. You bat voltage at running engine should be 14.5V at the pump.

Ranger
07-27-09, 08:28 PM
Please check the battery voltage. Bat voltage and fuel pump folw are connected,
higher voltage => higher fuel flow => higher pressure after regulator

and opposite. You bat voltage at running engine should be 14.5V at the pump.

Are you sure of this? I have never heard of any such thing. :hmm: Could this be something common to European fuel pumps?

Submariner409
07-27-09, 09:06 PM
Battery voltage might have some small effect on fuel flow and pressures, but at a normal voltage range of 12.8 to 14.6 volts the FPR should handle variations: that's what it's for.......

We run wet Carter pumps in our marine engines with voltage swings all over the place and no problems...................(Carter: Now there's a name out of the past.)

askimbenim
07-27-09, 09:46 PM
I agree that between the 12.8 to 14.8V the fuel pump, regulator etc. should guarantee the specified pressure in with a tolerance window.

If the voltage is way off that number (less than 12 or more than 15V) you will for sure have different flow rates of pumps, and the regulated fuel pressure (fuel pressure in the fuel injector rail or after regulator) will not match with the manufactorers specified values.
I can only talk about the regulators I worked on (Bosch Kefico), they showed different regulated pressure at different flow rates. For example you want to install a bigger fuel pump in an existing car (or system) the current fuel pressure regulator will most likely not be able to maintain the specified regulated pressure. Normally the o2 control (long and short term adaptation) would take care of that.
The gentleman tested 2 psi lower than the spec. I wanted to bring some light from my experience with pumps and regulator. Sorry for the confusion.
Askimbenim

Edahall
07-28-09, 01:31 PM
My voltage is around 14 V while the engine is running but perhaps I should check the battery voltage while it is cranking.

Submariner409
07-28-09, 05:37 PM
Cranking battery voltage will scare the hell out of you. Don't.

Edahall
07-29-09, 12:21 PM
Cranking battery voltage will scare the hell out of you. Don't.

Well, it's possible the battery may have something to do with it. I've had the car for 6 years and have never changed the battery. It may even be possible that this is the original battery which would make it 16 years old.

jeffrsmith
07-29-09, 01:59 PM
Back to Post #7 - Sub said to check out your fuel injectors - have you done that yet? If you replaced the fuel pressure regulator and the pump pressure is sufficient you need to check the injectors, it definitely sounds like one is stuck or intermittently sticking open.

If the car cranks ok and your voltages are 14~14.5 while running I would not worry about the battery.

Edahall
07-29-09, 03:51 PM
Back to Post #7 - Sub said to check out your fuel injectors - have you done that yet? If you replaced the fuel pressure regulator and the pump pressure is sufficient you need to check the injectors, it definitely sounds like one is stuck or intermittently sticking open.

If the car cranks ok and your voltages are 14~14.5 while running I would not worry about the battery.


Yes I did try to check for leaking injectors by pulling up the injector rail so each injector would be exposed and I could have access to see drips. However, when I powered up the fuel pump, instead of the injectors pressurizing, gas ended up getting dumped into the front drivers side cylinder. I have no idea where it was leaking from but possibly it was from the FPR. I ended up having to take the spark plugs out to allow all the gas to evaporate. The engine spewed a cloud of white raw smelling gas smoke the next morning when I started her up. The exhaust/CAT must have been full of fuel.

I am now looking for ideas on how to check for dripping injectors. Be aware that this is a 93 N* engine where the top of the intake manifold is not a beauty cover like on the 95+ engines. I should also add that I also did a resistance test on each injector and got 13 ohms on each injector. I also checked the resistance between the + and - terminals on each injector plug and they all tested out at 0 ohms. This should rule out a wiring problem. I have heard of reports of gas destroying the insulation on the wiring and causing them to ground out.