Rich Mixture, Misfire, Stalling

[SuspiciousPizza]

EA82, SPFI, 5MT D/R. 

My engine runs *okay* and can do short back an fourths to work alright.

However, it has a misfire. The entire throttle body (injector, TPS, and regulator included) is a "good used" part. My fuel pump is also noisy and I have no idea when it was last replaced. 

TPS is properly setup. Used the 2 feeler gauges. 

Once I've been driving for a while, sometimes it'll run like a top. Buttery smooth. Other times it idles rough. It doesn't buck the car side to side but it does vibrate. A noticable gas smell comes from the driver side and the plug for cylinder #4 has more carbon buildup.

I've had the engine stall 3 times after coasting to the bottom of a hill and pushing in the clutch. My guess is the rich mixture floods as I'm coasting and not burning all of it off. Then once I clutch in and the RPM's drop, the mixture is too rich and it just stalls. 

I've swapped in hotter plugs with a tighter gap, cleaned the MAF, and checked my timing (15deg BTDC. I'm using carbed cams on a SPFI setup). Coil, alternator, plug wires, battery cables, PCV, and CTS are all new. I don't have any codes. All engine hoses are new. 

My guess is it's the fuel pump, injector, regulator, or the distributor. (Cap and rotor only have about 3k miles on them).

Could also be a tuning issue. I have not fiddled with the idle control.

Any thoughts or ideas?

:]

[SuspiciousPizza]

I noticed something today while I was leaving work.

It's starting to get cold here so I let the car warm up without the heater running. As I was going to leave the first thing I did was turn the heat on. Hmmm. The idle dropped 300 rpm and started to sound like it wanted to stall.  

Perhaps I have some sort of vacuum leak and that's causing the issues. The EGR valve operates with vacuum. Maybe it's not operating properly due to vacuum loss. 

Perhaps this is causing my fuel smell? 

Some time in the next few weeks I'll run a D-check, do a fuel pressure test, and check for vacuum leaks. 

I've given the entire engine bay the smell check for fuel leaks and didn't find anything. I don't smell gas in the garage either after it's been sitting overnight. I do keep an extinguisher in the car though.

:]

 

 

 

[moosens]

Try the spray test on those hoses? While it’s running spray some WD-40 around the vacuum hose ends all over until you notice a change in idle. 
 

No funky smoke from the tailpipe ? A little white? A little black ? Normal ? 

[SuspiciousPizza]

No funky smoke. Exhaust definitely smells of fuel though. 

After I've been driving, the hot idle is at about 1k vs when I cold start, it'll sit around 750.

Could a vacuum leak caused by the HVAC system cause the EGR valve to not open appropriately? 

I bought the cheapest vacuum gauge from a decent brand I could find so I'll be hooking it up oil crisis style. Diagnostic tool + fuel savings.

I should also note I'm not 100% convinced I'm experiencing a misfire. It very well could be excess fuel in the exhaust burning off causing the illusion of a misfire when I put my hand at the tailpipe. I lack the experience required to say for sure, I'm definitely still learning.

Edited November 21 by SuspiciousPizza

[SuspiciousPizza]

I've been driving around with the vacuum gauge installed for a few days and here's what I've found (other than the constant roller coaster hills in my area destroy my fuel economy). 

On a cold start the vacuum seems quite low (13-15 inHG) and it flutters (correlating with a rough idle on cold start) within a range of 1-1.5 inHG. After the engine is at full operating temp, at idle it'll sit quite steadily at 20 inHG. However, my idle has a rhythmic roughness where the vacuum will drop about 1 inHG and it'll flutter slightly more when it drops. The rhythm is about 2 seconds smooth idle then 1 second rough idle, smooth, rough, smooth, rough, etc. 

My vacuum seems on the low side so I'll get some fuel pressure gauges spliced in and see if advancing my timing to the factory spec of 20 BTDC smooths anything out.

Any ideas or thoughts are appreciated.

:]

Edited November 25 by SuspiciousPizza

[RoadnReel]

Sounds to me like a timing or air issue. I would bring the timing to 8-10 degrees BTDC because of the carb cams and see what happens. You said you cleaned your MAF, so that shouldn't be a problem, but your O2 sensor could be sending slow signals. 

[SuspiciousPizza]

I do not have an O2 sensor nor an EGR temp sensor.

My coolant temp sensor is a good quality sensor and it's basically brand new. New doesn't mean good, I haven't tested it but I'd be rather surprised if that was the culprit. 

The car has always had a fluttering idle, even with a completely different engine. 

Also it's a D/R so there's no 4WD vacuum assembly like on a SR4WD. I wouldn't be surprised if the HVAC system has a leak. I'll give the hoses behind the dash a look.

Interestingly the vacuum flutter on cold start isn't as bad and subsides much more quickly if the oil was preheated. Maybe one cylinder has bad rings?

I brought the timing up to 15deg and I was pinging on regular. No issues with pinging when running premium. The heads have been resurfaced for sure once. No clue on their prior history.

I'm not sure how the ECU learns mixture and timing curve but perhaps the ECU is expecting SPFI cams and the carb cams are making it freak out? I doubt this but it's a thought I had.

Edited yesterday at 01:14 AM by SuspiciousPizza

[el_freddo]

I doubt there will be too much of a difference between carb cams and EFI cams. Turbo to NA cams, yes, quite a difference but even then the ECU wouldn’t care too much if at all. 

Cleaning the MAF can induce loads of issues if not done properly. Even then, many seem to report that the MAF is never quite the same after a clean if not done gently enough. 

Not having an O2 sensor would be an issue for the ECU. Why is this missing from the system? 

As for

timing and pinging, my brumby sits on 4°btdc and runs the best RON “pump gas” we can get (98RON). Any more timing and it pings its tits off. Summer driving can be an issue with pinging at times. 

If your HVAC system is leaking vacuum that can be fun to diagnose - unless it’s a hose off which will hiss when selected (if post dash switch) quite loudly, enough to know you have a leak. The actuator diaphragms might mask the noise a bit better, however, in my Lseries with 530,000km on it they’ve never been an issue and not replaced in my ownership of 20+ years. 

I hope you get this sorted. Nothing more annoying than these little issues with no obvious solution. 

[SuspiciousPizza]

I believe not all SPFI cars here in the US came with an O2 sensor. California has more strict emissions regulations than the rest of the nation. The California cars got O2 sensors, the cars sold in all other states do not have O2 sensors. I believe. Regardless, not all SPFI cars have O2 sensors from factory. 

I have found it interesting that despite my car originally being sold in California, it doesn't have California-spec emissions equipment. It has the national standard emissions equipment. 

I believe the national standard is just an EGR setup and a charcoal canister. No O2 sensor and no EGR temp sensor.