Alright, I have had a problem with my car that I believe is the same and has been manifesting for the last 7 months somewhat on and off.
7 Months ago, I began experiencing engine bogging and acting very weird, this was on the stock ecu etc. so no way to be sure but I think it was running lean. If driving under full throttle or just idling along in a parking lot, it was fine. When cruising however at light throttle, the car would suddenly sound lean and begin to bog. I wasn't sure what the issue was and after using the built in DIAG pins and counting the engine light flashes, it said it was something with the Air Flow Meter. I already had acquired a Megasquirt3x at this point so I figured I would kill two birds with one stone and install the MS3 and get rid of the airflow meter and fix my problem.
Got the car running, took it to a guy that works with Goodwin Racing here in San Diego and he helped me fine tune it a bit more and I learned as much as I could from him. Car was mostly running great but then a few weeks later I began experiencing the same issue again, at least this time I had a wideband 02 and could see what was happening. Same problem, under cruise light throttle sometimes the car would just jump from 13-14 afr to 17-19 afr. I ended up putting in new plugs, new ignition coil, and the car seemed to run better again for a few weeks.
Then the problem came back. This time, I suspected maybe the injectors as they were the originals, I was planning on turboing soon and had most of the parts around so I figured i'd swap my new 450cc injectors in. Car ran better again for 2 more weeks!
Then again, I tried cleaning all the grounding points on the motor, seemed to help for a week or so, then it persisted.
Braineack helped me through some emails get my Accel Enrichment settings corrected and better and once again I thought it was fixed.

It has been steadily getting worse and happens almost all the time now over the last couple weeks. I put in a new fuel pump because after doing my intercooler and piping I suddenly had no fuel pressure. I discovered if I jumped the GND and FP in the DIAG panel under the hood and turned the key that then I had fuel again. Figured it was the Circuit open relay and I ordered one, hasn't gotten here yet, but the fuel pump started working again without jumping it two days ago after I got my gauge pods mounted(not that that has anything to do with it, but that was when it started working again).

Anyways, I am at a total loss here and am very frustrated and just want to get the car running well and running RIGHT. It drives under heavy throttle perfectly fine but when trying to drive like a normal person it is starting to drive me nuts.

Does anyone here have any other ideas as to what may be causing this? List of parts I have done over the last several months(yet the problem has persisted) are, Megasquirt, Seq injection harness, AFM delete, Intake Manifold Gasket, new 450cc flow tested injectors, fuel filter, fuel pump, new spark plugs, wires, and coil, turbo and IC etc., and as far as the motor is concerned I think that is about it.

I can post any logs or tune info anyone asks for, I am just desperate and out of ideas at this point. Thank you for anyone that offers input and help.

 

Hook a fuel pressure gauge up to the car, and see if your fuel pressure is dropping when this happens. That will confirm or eliminate a hardware (fuel system) problem from a software (tuning) problem.

 

Is there anywhere I can hook up easily so I can monitor while driving or do I need to T into the system pre-fuel rail or what?

 

Tee in pre-fuel rail and hook a gauge up, run the hose to a guage you can see and watch it while driving.

 

I'll try that, though I think its unlikely as almost everything in the fuel system is new, and it is totally fine if I add a little throttle. The problem also persists when I bypass the Circuit Open Relay, which is why I'm confused as to what it was exactly that failed in the first place and started working again a few days ago.

 

Does it only happen after driving the car for say, 50min or so? As in it's never done it on a less than 30 minute drive, only after extended driving?

 

Nope, work is 15 mins away and it starts up as soon as I'm up the hill from my house and back on the flat road less than 5 min away.

 

Then it isn't vapor locking. Test fuel pressure as I said, that's where I'd start.

 

10-4, will try that tomorrow and report back.

 

Alright, I put a Fuel Pressure gauge in and T'd to the line from the pump before the fuel rail and at Idle it was giving about 32-33psi of pressure. If I gave it throttle, it would rise to about 40-41 but go no higher. Also to simulate full throttle I pulled the vacuum hose off the FPR, gauge read 40. Is this a bit low? I am now thinking the Fuel Pressure regulator is my issue, I have replaced the inline filter, replaced the pump and tried another spare. Is there anything else in the fuel system on this car that would lead to my issue? Like I said I randomly had no pressure for like 2 days and had to bypass in the Diag box, but that went away. I will likely be replacing the circuit open relay under the dash so that doesn't happen again...but I believe these were two separate issues.

 

I dunno what OEM pressure should be. But you need to hook that gauge up, and watch it when the problem happens to see if your fuel pressure is falling. That will rule out a lot of potential hardware problems (pump, regulator, filter, relays, wiring, etc).

 

OEM is 43.5 for an NA.

 

I had a similar problem and it ended up being my cas. I replaced all my fuel stuff as well as a precaution. Have you tried pulling the fpr and cleaning it a bit? I've seen them for about $10-20 on fs pages, maybe you could try that route?

 

I hooked the gauge up, I could not drive the car because I had nothing long enough to pull the gauge into the car with me, but I can make the car cause the same lean condition at idle with a bit of throttle. Its as if I am hitting the throttle slightly and allowing more air in, but something else wont compensate. Thats what it looked like on the fuel pressure gauge. I would give it a little gas, and it would start running lean up to 17-18 at around 3.5kish RPM's under easy throttle and had about 32psi of pressure at the fuel rail. Once I gave it a little more throttle there would be a jolt and fuel pressure bounced up to 41, and the motor would come back down to 12/13AFR running smooth as silk.

Thats the exact thing that happens when I'm driving if your not giving enough throttle and sometimes it will jolt back right. Never does it if you are consistently giving heavy throttle.

 

<p>I would say replacing the FPR is on your list of things to try.</p>

 

The 1990 FPR can't be taken apart, and I didn't read enough info on it to make me decide to spray carb cleaner or something in to clean it, dont want to make the diaphragm worse potentially. If you know of a good way to clean it though, I'm all ears!

 

<p>If it was the CAS, that should show up as sync loss on a log i would think.</p>

 

Yea I had brain look at my high speed teeth logger and it looked fine to him.