92 mariah hesitates at acceleration

[wcoarsey]

I got a 1992 supra mariah with 351 ford and protec ignition. My problem is: As I begin to accelerate the engine skips and will choke down if I do not back off on the throttle a bit. The more the weight the more the issue. This has gradually gotten worse over time. It idles fine. I am pretty good with engines but this one is tough.
Things I have tried include: new fuel filter, new fuel pumps (both), new plugs and wires, new injectors, new map & baro sensor, new ignition and system relay, and even new PROTEC ignition module.
I have checked knock sensor, water temp sensor, oil pressure switch, compression test.
The only thing left that I know of is (TPS) throttle position sensor and it will be in Tuesday. I have no clue what is going on. I thought the ignition module would solve my problem. I am pretty sure it is electronic. The injectors all draw back at once for a brief second only on acceleration. The faster I accelerate the worst it gets. It seems to be running rich not lean. any suggestions?

[OUI]

Sounds like your advance mechanism on the distributor is not working. Before you buy a new distributor, squirt some WD-40 into the breather holes, that may help loosen up the mechanism

[critterCQB]

So glad I read this post, I'm having the same problem.

[DKJBama92Mariah]

OUI, ProTec Ignition doesn't have a distributor; it is a coil pack system and it sucks very much bad.

Its looks like this
http://img.photobucket.com/albums/v55/dkjpika/Boat/IMG_0452.jpg

Wcoarsey,
Welcome to the forum!

Does it do the same when you rev it in neutral?

Where does it begin to cut out ~2000rpm?

You should be aware that the Pro-tec system has a few sensors of its own separate from the sensors that feed the gauges. The protec temp sensor is at the back of the portside cylinder head. The oil pressure sender should be in roughly the same spot as the one for the gauges.

[wcoarsey]

DKJBama92Mariah- yes, mine setup does look like the one in the picture; however, I have another computer pack behind or under the coil and ignition module. In neutral it revs perfectly fine, even with a water house hooked up and in gear it will really rev well. I have tried all the sensors as far as I know. I might go back over them in the morning though to be sure, what do you think about the throttle position sensor? if I slowly accelerate it does much better than getting on it, but still cuts out. thanks

OUI- mine has a interrupter which is very similar to a distributor. I have thought about that. My timing is dead on at idle. I don't have enough specs to test the advancing on it. I have been told that it being sent from the computer as a signal makes it more unlikely to be faulty in the advancing, but still I question that myself. will look into it. thanks.

critterCQB- if yours is very similar, I have been told 90% of the time its the protec computer module, pretty pricy around $500 I think. skidim.com has them. If you call ask for Vince. He new the colors of my wiring harness off the top of his head. pretty impressive guy. goodluck

[wcoarsey]

oh yea, it cuts out at random rpms but haven't watched it as close. will check that more in the morning.

[DKJBama92Mariah]

The TPS is always a possibility, but i really don't think so here. You would think TPS would either act up all the time or not at all; instead of only under load. You can test it by moving the throttle through and measuring its resistance from closed to open. It should scale fairly smoothly without jumping all over the place.

The one electronic sensor that jumps out to me that could causer your problem is the MAP (manifold absolute pressure) sensor. It is essentially a vacuum gauge for the ECM. The ECM uses this data along data from the TPS and other sensors to determine the proper air to fuel ratio. You can test this sensor by purchasing an inexpensive handheld vacuum pump at autozone or some other local parts store and using it along with a multimeter to check the resistance of the sender as vacuum levels change.

For the best interests of your boat and your wallet, please take a look at the PDF at this link http://www.correctcraftfan.com/Downloads/Pro_BOss_GT-40_Service_Manual.pdf

Just throwing parts at a problem can often fix it eventually, but it's almost always cheaper and quicker to diagnose first, then repair.

The beginning of the PDF gives you a good overview of how your EFI system works. Pay special attention to the first full paragraph on page 32 of the pdf.

I wish I could help more, but i've just never worked on a ford efi system.

[wcoarsey]

UPDATE: it wasn't the (TPS) throttle position sensor. PCM sent me a manual and plan on checking all the wire voltage today. Maybe something will come up. I now think it is something to do with the map sensor. I did replace it, but I haven't check the voltage or anything else. Really hope something pays off today.

[Dinoz]

I had the same problem with my '89 Comp and the solution to the problem for me was rebuilding the carb. I found that another problem was my fuel millage wasn't good at all when I had the choking issue. The hesitation was the worst pulling a skier. Now that I've had the carb rebuilt, the problem is gone. Start with the simple stuff first... good luck!

[DKJBama92Mariah]

DINOZ,

Good to see you back buddy. His motor is EFI