N/A Hesitation/Cutting out
 

I picked up a GSL-SE with an 86 N/A motor from a friend. The motor has 60k on it and my friend said it ran really strong before he swapped it into the GSL-SE. The car sat for 3-4 years and I'm here to finish everything up, so I can daily this beast. The car idles solid and under very light throttle seems to drive fine.

Whenever I give the car a little heavy throttle it will buck/sputter/cut out. I'm still trying to figure out why the tachometer doesn't work, so I have no idea what RPM this is happening at (assuming that it's happening at a certain RPM).

Even when the car isn't in gear and I rev it up with heavy throttle input it hesitates. It's not nearly as bad as when I'm actually driving the car though.

I took the LIM off and replaced the sleeves with Pineapple Racing sleeves and made sure the aux ports move smoothly, which they do now. I don't know if I should risk flooring it or anything to see if the aux ports are opening.

Any ideas on where to start diagnosing? I was thinking of tracing the wiring to the secondary injectors to see if they are kicking on..anything else?

Video...kinda hard to tell, but the motor hesitates a bit when I free rev. Like I said though when I drive it it actually bucks the car.

Not sure I saw what you were talking about. It sounded like it started at the beginning of acceleration, but it was pretty hard to tell. Does it seem to be tied to a particular RPM, or a particular throttle condition (range, movement, speed, etc.)?

Bah...I'll get a better video tonight. It seems to be tied to throttle input rather than rpm. Though it does bog if you just go full throttle from idle.

A good start is always to pull the ECU Codes, regardless of the issue it will give you a good baseline as to whats going on.

If the tach doesnt work your issue could be ignition/ coil related. Are you sure the swap has been completed correctly? no missing grounds or loose connectors? Simple things can often make the difference

Its a first gen with a motow swap, pulling codes probably isn't an option

What series engine was put in it?

When it comes to the tach, it gets it signal from the trailing coil, on FCs IIRC it is a yellow wire, if your trailing coil isn't fireing either could be your problem as well

Another issue, the car sat for 3 years, have you replaced the fuel filter? Dropped the tank and replaced the sock? When were the injectors last serviced? All these fuel related systems SHOULD be cleaned/replaced after sitting for over a year as gas turns sour after 3 months if not less

Fuel tank was dropped, cleaned, etc. Fuel filter and sock have been replaced. I can see if pulling codes is an option. The car does have all the smog equipment in place and working. I don't want to, but if they end up being the issue I'll send the injectors out to be serviced.

One way or the other, you can bet that it's tied to either the fuel system or the ignition system. Black box electrickery adds another layer, but you should be able to narrow it down to a few testable components simply according to what's at play/in flux when it misbehaves.

not quite, he's dealing with a FB with a s4 engine in it, the BIG question is, was the complete engine harness transferred with the engine? or was the original GSL-SE wiring hacked up to make this engine run? If its been hacked up, theres a plethora of possibilities that could lead to his problem

Also OP, I DOUBT you'll be able to pull codes, your gonna have to diagnose this the old fashioned way

my steps would be:

1. Check the trailing coils to see if they are sparking, if not, check to make sure they are getting power and ground
2. Check the wiring, see if its hacked up, if not, look at the FSM to see what wire runs the tach
3. if 1 and 2 checks out, check for vacuum leaks (doubtful, but still a possibility)
4. Check ALL engine/computer grounds
5. if 1-4 check out, make sure the injectors are getting signal to fire, and make sure they are spraying fuel
6. if all the above are good, then send the injectors out for service

Did not realize "GSL-SE" meant FB... Also did not realize how thoroughly one could divorce the operation of the engine from the black box electrickery. That warrants investigation...

Went for a drive

Better video of me free revving it. At 4k it hits a brick wall unless I ease into the throttle and even then it breaks up around 5k. I already spliced in extra grounds for the ecu, so I don't think it's a grounding issue anymore. I'm sending the injectors out to be cleaned/flow tested to rule that out..still looking for ideas.

try a new fuel filter yet?

P/O said he put a new one on when he dropped the gas tank. I'll replace it for the heck of it I suppose since I'm going to have down time while the injectors are off being serviced. I think I may try to trace the wires from the ECU to the secondary injectors to see if the circuit is unbroken.

Still exactly the same...at this point should I be testing out other ECU's, MAF's, etc?

Sounds like a very bad3800 hesitation.
Check all your grounds first, making sure their nice and clean and tight. Emphasis on the ECU to engine, then engine to battery

come on Nick, you should know how to diagnose an FC by now. lol

i also hear detonation so be sure your ignition wires on the trailings are going to the proper rotor, check CAS timing, etc.

i also hear the fan more than the exhaust so either your fan is stuck on completely or your exhaust is plugged up and needs an enema.

beyond that check the fuel pressure, that will cause a major issue with power like this especially at the transition after 4k. follow that up with cleaning the injector ground under the UIM to the rear rotor housing.

There's no fan on the car at the moment lol. I think you're hearing the air pump. The exhaust probably is clogged a little. It has the pre-cats and the main cat on it still. The exhaust smokes a bit when I idle the car up to temp. I didn't want to buy a header or anything until I got the POS running right and smogged.

As far as grounds go - I've cleaned/sanded the connection point under the UIM on the rat's nest. I've also cleaned and sanded the grounds that I could find by the shock towers. I'll have to check if I've cleaned the injector ground to the rear housing though...if it helps I've spliced into the ground wires pretty close to the ecu to ensure that they are grounded.

I guess the next thing I can do is get a fuel pressure tester from Oriley's and see what it's putting out.

they loan them also if you don't want to fork out to actually buy one, just get your money back after you're done with it. as for the exhaust, try dropping it and inspect it to see if it looks clogged, or loosen it up and see if it revs freely with it loose. also be sure to check your timing and wires, i hear what really sounds like preignition from some possibly really fucked up timing.

Found out that my trailing plug wires were mixed up. I put them back where they belong and nothing has changed:

https://www.youtube.com/watch?v=Qiri...ature=youtu.be

This weekend I will test fuel pressure and check timing.

something has changed though, the engine damaging preignition is gone now. (loud metallic popcorn sound)

Progress! I guess...

from buying cats off these cars for many years i've found that the pre-cats are notorious for failing...40-50% of the time when i get them the catalyst inside has failed, melted or broken apart. the main cat is usually still good. if you end up taking them off and find that you need to replace the cats i buy them for scrap, which is usually about half of what you'd pay to get a new cat/cats. message me if you go that route if that's the problem...

i got 3 main cats left

they're still good, the FD main is still almost brand new but the damn EPA is such a fucking pain in the ass.... regulating sales and requiring you buy a junk $100 inferior CARB cert cat instead or pay more than the car is worth for new OEM.

the other cat guy who came by said the FC main cats(i have 2 left) were only worth $60 each, i gave him the finger.

I have access to a header, but it's a true dual...so it won't mount up to the main cat =/