Stuttering past ¼ throttle

86, 22re, manual. Having a problem pinpointing this issue.
It drives fine until I push more than ¼ throttle. At that point it feels like it's stuttering like the timing is out. Sometimes it will push thru the issue and power comes back, sometimes it doesn't.
Timing is correct, new cap, rotor, plugs, and wires, fuel filter. Fuel pressure does not deviate at any point and stays steady at 35psi.
No difference if the fuel tank is low or full.
No vacuum leaks either. Stumped at this point.

 

Throttle Position Sensor tested?

 

Nope. Overlooked that. Thanks!

 

Check that the intake tubing doesn't have any leaks or cracks also.

 

Sounds like a maf sensor all day.

 

You beat me to it. I was thinking the same as you. I had a similar issue with a different vehicle and a can of maf sensor cleaner spray fixed it.

 

does BDR for you name stand for big pickle Rick?

if so, hats my friend.

 

https://youtu.be/ravi4YtUTxo

“You have a gift my friend “

 

Thanks guys. I believe I have a spare MAF that I will try.

 

let us know

 

https://m.youtube.com/watch?v=AynXoLjYrKc

 

I'd also look into your new plugs - shuddering under load can be caused by cracked plug ceramic

 

If that were the case it wouldn’t be so load dependent.

but still possible

 

The symptoms are nearly identical to when I made the same mistake on a previous vehicle. You could somewhat "push through" the stumbling but it would still fall on its face now and again during acceleration. Luckily this was a built engine turbo Mazda and I always had like 2-3 sets of extra plugs on hand.

 

We shall see….

if you have to keep 3 sets of plugs on hand, you did something wrong….worked on many of the speed 3 motors and they were quite reliable.

only issue was when you had to actually break it open it was much easier to pull than work on in place.

 

I found that the spring clip was missing from the tps plug, so I ordered a new plug harness. Not stating that as the culprit, but who knows. I'm going to tackle the truck this weekend and will let you all know.

 

I would have assumed fuel filter. But that's old school i guess.

 

Also check the airflow meter (as it was called back in the day) if so equipped. My 1988 had a similar problem and the butterfly was binding. WD-40 on the pivot points fixed it.

Oops, thought I had posted this yesterday.

 

I made a lot of changes and generally would swap plugs every 1,000mi or so and/or any time I modified the tune/dyno'd the vehicle or went to the track.



I built the motor myself after popping it at 160k running a GT3076r on meth. After the rebuild made about 600 to the wheels on a Precision 6062 around ~32psi lol

Anywho back to the original post. Just wanted to share my experience and always have fun reminiscing on my days in the Mazda world.

 

I already changed the fuel filter and hooked up a fuel pressure test tool, then took it for a drive and the pressure stayed solid at 35 psi even when the stuttering was happening. I've ruled out the fuel system on this situation now.

 

I spent a lot of time on my 86 with erratic stutter and stalling. Ended up being a valve adjustment issue. The exhaust side valves were too tight. Adjusted all of them to factory spec and it’s ran great ever since.

 

well you didn’t get to have to fancy with it….

here I thought my hx35 1.8t @ 23 pounds on pump was gonna show you…..

edit: who did the tubular manifold?

 

It was made by FJ performance (some random shop in PA). I believe they bought the design off of someone though. It flowed very nicely and sounded awesome.

 

On my list now. Thanks!

 

Update..... Cleaned the MAF, cleaned throttle body, checked the plugs, and replaced the TPS pigtail.
Not sure where the blame belongs, but I'm pretty sure the TPS plug being loose and the connectors in it looking to far open was most likely the issue.
Glad to report the motor does not stutter any more.
Currently doing a valve adjustment check to just be sure all is well.
Thank you all for your help!

 

And it's back. Found out the ecu is from a 85 2wd auto. May be an issue.

 

Years ago I had an old Dodge truck ('88 D100) with a similar problem. At idle and light throttle it was fine. Anything past that and it would stumble and nearly die. Turned out to be the EGR valve. Diagnosis was easy: disconnect it and all was well. Once replaced everything was fine.

Just a thought. Not sure that's applicable here.