1.) Does it HAVE to be at 3800 RPM or will this happen at other engine speeds as well?
(The problem with the car I'm driving occurs mostly at 3800-4000 RPM but has occasionally exhibited itself at 5000 or 6000 RPM dependent on load.)

2.) Will it just stumble at 3800 RPM and continue to rev up if you keep on trying to accelerate, or does the car hit a brick wall as if a rev limiter is at 4000 RPM?
(The car does both sometimes... Usually, if I baby it up, it'll continue. If I'm accelerating hard, it'll quit at 4000 RPM and will not accelerate any further.)

3.) Can this problem be intermittent?
(Based on the above two pieces of info, I can say that the problem is definitely intermittent.)

4.) If the ground under the manifold is bad enough or combined with other minor problems such as a misadjusted TPS, will it cause a failure to start?
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/need-some-help-n-engine-bogs-down-cuts-out-832666/


The car in question is a 1988 GTU with a 1987 (Low impedance injectors with resistor pack) engine in it.
The 1988 GTU was purchased with an overheated engine, the replacement engine came out of an early 1987 automatic base. Swapped flywheels, but otherwise didn't touch the keg.
Used the wiring harness out of the 1987 to retain the resistor pack. Also, the 1988 harness could have been subjected to heat damage from the overheated engine, so I didn't want to use it.

Have already swapped the following parts with a known good vehicle:
-coil packs
-ECU
-Air Flow Meter

Have already tested with a multimeter:
-TPS (Adjusted a few times as well)


As far as testing goes, would it be a good test to find the ground pins on the ECU and use meter probes to backprobe and put a chassis ground on them, or should I go ahead and engine ground them?

 

i was having some issues with hesitations and what not.. this is what i have done in the past few weeks and problem doesnt exist anymore for me.

Used some red stereo wiring from junk yard *the small gauge kind for aftermarket amps*, one lead from neg battery terminal to firewall, than a short one from firewall to top of intake manifold. Cost - Free
*probably wont do anything if your engine is already correctly grounded, but added piece of mind that it wont be a engine grounding issue*

Checked timing and adjusted/corrected + new spark plugs. Cost - new spark plugs $20-25

new fuel filter/fuel sock in tank. Dont run cheapo brand gas.

Make sure to adjust the TPS. Check for vacuum hose leaks etc.

 

^

Already done the above... Timing was checked, Spark plugs are good (Why would one use old spark plugs when doing and engine swap?) and the fuel filter was changed...

In addition, the cat was removed and an RB presilencer was put in as someone thought the cat was clogged.

 

Bump.

I'm trying to diagnose if this indeed the 3800 RPM problem or another problem entirely... Or perhaps some combination of problems.

 

Another bump...
It sometimes occurs at 5000 RPM and sometimes at 3000 RPM.
I never really can tell when it will or won't do it.

Usually it won't do it in lower gears (1 and 2)
And usually it will do it in the upper gears (3 and 4)

It will do it with the TPS disconnected.
It will do it with the 6 port actuation backpressure line disconnected.

Currently the 6 ports are connected to the Split air pipe hose through a series of adapters to actuate by the air pump. The split air pipe is removed along with the catalytic, a presilencer is in its place.

 

Check the fuel pump sock. My car was hitting a brick wall around 4k-5k rpms. I mean it was like you turned the key off and back on again. I pulled the pump out to find the sock had come off the pump and was sitting on the floor of the tank about a foot away. I went ahead and bought a new sock, put it all back together and she's back to normal. It appears to me that the sock isn't just for straining contaminants, my guess is that it helps to create a "baffle" effect and possibly an aid against cavitation???

 

Sounds like a fuel problem, it can be anywhere so it is best to do all you can afford to replace and clean all of the fuel system. I started with the fuel filter, (went backwards) bught a new sock, my problem was bad secondary injectors. You can get the professoinaly cleaned fo about $50. since your problem is in the 3800 - 4000 rpm range I would say that is your problem because that is when you secondaries kick in. Change your fuel filter before you reinstal your injectors or else you may wind up wasting your money getting them cleaned the first time you crank your engine.

 

Would a fuel problem be that intermittent? Will I have to drop the tank to get at the sock or is there a little hatch under the carpet?

Fuel filter is new, but I always blow through an old filter to see what comes out the inlet side of the old one. It was nasty... Brown and little flakes in the fuel. It does make me wanna check that sock.

 

Oh yeah deffinetly, fuel problems are the most intermittent. Especially with the additives in todays gas. If you blew gunk from the filter you may as well trash it and go straight to the tank. I would suggest changing the sock, to do this in a 7 is a dream compared to a new yorker!!! There is an access panel under the carpet on the drivers side, you might get lucky and not have to deal with the rusty screws like I did.

Chances are you change the fuel filter and the sock you wont have anymore problems.....but I seriously suggest that you clean your secondaries though. Here is what I do in the case that you don't want to pay to get them cleaned but want to find out if it is the source of the problem. Pull out the injectors, take a can of carb cleaner spray inside and let it sit. Meanwhile find an old cigarett lighter charger for a cell phone and cut the plug off and bare the wires. Plug this in and touch the wires to the leads on the injectors. Do this over and over running plent of carb cleaner through the injectors. Last take some fuel injection system cleaner and pour it into each of the to injectors doing the same thing with the charger. (the fuel injection system cleaner acts a lubricant for injectors) put the injectors back in and take it for a test drive.....I will almost guarantee results.

 

man did i not suggest checking the fuel sock/filter? lmao

good luck let us know what happens.. it could be ecu too