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'93 940 turbo stumbling and dying

widewagon92

now with more caffeine!
Joined
Apr 25, 2020
Location
Maryland
I finally have my wagon back on the road after taking way longer than planned to finish the t5 swap, and unfortunately some of the issues I had before the swap have stuck around.

Engine is a '93 b230ft with an rsi stage 1 cam and ported 530 head. 16t turbo, yoshifab bracket and mamba wastegate with a cheapo amazon downpipe welded on, rest of the exhaust is currently disconnected. New ngk wires and plugs, distributor rotor and cap aren't new but are far from toasted. Adjustable cam gear but no advance or retard is set. Green giant injectors, 012 maf, k&n cone filter and an ipd silicone intake hose. Stock ecu and ezk with KL racing chips to match the injectors and maf.

On first startup the idle likes to bounce, but it's in that 600-1k range I've read is the norm. I let it warm up for a few minutes this morning, drove it to the end of the driveway, and it stalled. Took it the rest of the way to work and while it drives fine when driving normally, if you take your foot off the gas while the car is in neutral it'll stall and die. Rev it up a bit and eeeeease off the gas, and it'll (sometimes) do a bouncy idle right around 500. Stab the gas and the car will stumble and pop, roll into it and it seems to do fine. Fuel pressure is fine at both test valves. Vacuum line off the pressure regulator smelled like gas, replaced the regulator but no change.

I have an aem wideband installed, can't get it to display anything but (---), going to try hooking it to different power and ground sources and see if I can get it to read. At this point I'm thinking either my wastegate or my ecu has failed, anything else I should mess with while I try to get the wideband working?
 

widewagon92

now with more caffeine!
Joined
Apr 25, 2020
Location
Maryland
Pulled the injectors off a yard car myself, ran them through an ultrasonic cleaner and rebuilt them before installing. They should be okay but I don't have a flow tester, should I pull them and check? Maf was purchased from a forum member I trust, blew the dust out with canned air before I installed it but I can check if it's picked up some dirt.
 

widewagon92

now with more caffeine!
Joined
Apr 25, 2020
Location
Maryland
Doh, didn't think to check these. I checked my iac hoses for leaks or splits but didn't pull the damn thing to check and clean it. Haven't set a tps or throttle blade before, found this guide so I'll give it a shot. Thanks!
 

widewagon92

now with more caffeine!
Joined
Apr 25, 2020
Location
Maryland
Back with an update, tested my iac and discovered it had bit the dust. Plugged in a spare and the car wanted to idle at 2.5k! So I went through and set the tps and throttle blade properly, idle is a little low now but the stalling has stopped. But like a hydra, two new issues have risen:

Doesn't matter if you floor it or roll into it, once the boost gauge reads 10psi the car stumbles hard and pops and bangs like it's two-stepping. This is also usually when it's around 3.5k rpm, but this doesn't happen if you're just revving it up in neutral. Also, the car seems to idle better with the o2 sensor disconnected, but the popping still happens with it unplugged while driving. Wideband is in but stays at 14.6 to 14.8 while idling, driving etc. Sometimes goes into the 15s for a little bit after the banging, but I'm not convinced it's reading correctly.

Could the o2 be causing this? It's only four months old and for most of that time it's been sitting it a car on jack stands.
 

dl242gt

The world of the smiling Dogo
Joined
Jun 21, 2002
Location
S NJ, a suburb of Phila.
Seems like a good description of spark blowout. What is the plug gap at? How old are the plug wires, and cap and rotor? A weak spark gets blown out in the combustion chamber.

You may reduce the plug gap to around .026 if it keeps happening even with a strong spark.
 

TheLoganZilla

New member
Joined
Oct 5, 2020
Location
Morris County, NJ
Doesn't matter if you floor it or roll into it, once the boost gauge reads 10psi the car stumbles hard and pops and bangs like it's two-stepping. This is also usually when it's around 3.5k rpm, but this doesn't happen if you're just revving it up in neutral.

Had a similar problem with my 940 turbo a while ago. I'd seriously consider checking the high-pressure fuel pump; one that's going bad will deliver enough fuel for idle fuel pressure to check out and also for a no-load rev to work fine, but under load or boost it will go lean enough to cause those pops and bangs. Replacing my fuel pump solved my issue.
 

Marvelous3

Who engineered this?
Joined
Nov 12, 2002
Location
Atlanta
Spark blow out on my red wagon was like:

Car runs fine
Mash throttle into third gear out of overdrive
Rpm would get to about 3500
Engine would cut out
Let off throttle
Engine would fire back up again
Rinse repeat

One step colder plugs fixed the problem. Bpr8?s i think.

9/10 youve got a vac leak somewhere if the idle is hunting. It won?t run right without the ecu getting a signal from the o2 sensor.
 

widewagon92

now with more caffeine!
Joined
Apr 25, 2020
Location
Maryland
More updates: Installed colder plugs, ngk bpr8es. Popping and banging got better, but was still there. Advanced timing 2 degrees via adjustable cam gear and it's all but gone. I'm now getting an issue that almost feels like clutch slipping. Rolling into it or punching it in 3rd or 4th makes rev normally until the spot where it was struggling before, and then it revs up as if it was in neutral, car doesn't move any faster when this happens. Wideband reads 14.6 while idling or driving around at low rpms, higher revs I've seen it climb to 16.6. Full throttle doesn't get the boost gauge any higher than 6psi.

During this latest round of troubleshooting, the tach also stopped reading correctly. Would sit at zero at idle and read whatever it felt like while driving around. This fixed itself between putting in the colder plugs and advancing the timing.

Checked all my grounds, we're good there. Visual inspection found no cracked hoses, uncovered ports or other vacuum leaks, going to pick up a can of ether and see if I can find any that way. Also going to jerry rig a fuel pressure gauge to watch pressure while under load. Anything else I should check?

What's a good filter over the k&n? I've heard they let a bit of grime in, but couldn't find a filter besides theirs that didn't have a metal bit inside the filter. Odds are probably low of the metal bit detaching and venturing into the turbo, but it still worried me.
 

dl242gt

The world of the smiling Dogo
Joined
Jun 21, 2002
Location
S NJ, a suburb of Phila.
Did you make sure to gap the new plugs at .028"? I'd also spend a bit of time checking the connections on the ignition amp and the make sure the terminals on the coil are clean and tight. You can put some OX Guard in the connections to protect them.

Does seem like clutches slipping with the way you describe the revs.
 

widewagon92

now with more caffeine!
Joined
Apr 25, 2020
Location
Maryland
New plugs came out of the box at .028, I re-gapped them to .026 since that's what I had the bpr6's at. I can put them back to .028 and see if it makes a difference. Ignition amp is the unit on the driver's fender by the battery right? I'll give that a check. Considering replacing the cap and rotor at this point, I don't want to go full parts cannon but if it'll remove a variable it might be worth it.

Could the exhaust being just a downpipe mess with the o2 sensor's readings enough to cause this? There's a solid 8 inches between the factory o2 and the end of the pipe, I'd imagine that's enough for the ecu to get a good reading.
 

dl242gt

The world of the smiling Dogo
Joined
Jun 21, 2002
Location
S NJ, a suburb of Phila.
Make sure you check the inside of the cap if you have a head mount distributor. It may be getting oil in there from the head. That will cause ignition missing and stalling.
 

widewagon92

now with more caffeine!
Joined
Apr 25, 2020
Location
Maryland
More updates: car now has a full 3" exhaust, I can drive without going deaf now but not much else changed from that. Pulled cap and rotor, no oil inside there. Took it for a short drive and afr's kept getting too high with anything above medium throttle, bucked hard a couple times in third. Checked after the drive and it had blown a couple vacuum caps off the intake. Replaced those, went around with ether testing the injector seals and intake manifold gasket while idling and couldn't find any leaks.

The most interesting development is the maf. Twice on a test drive the car really bogged down, bucking in all gears and almost stalling in neutral. Pulled the plug to the maf during idle and it kept running, so I swapped in the old 016 maf. Idle came back, car now pulls harder than it ever has and the afr's haven't gone above 15. Could this have been a faulty 012 maf the whole time?

Clutch is definitely slipping if you step on the gas too fast. Roll into it in 3rd and 4th and it holds, but floor it and it revs up, builds boost and you smell toasty clutch. My cable definitely needs adjusted but the clutch isn't dragging, this issue has me second guessing my installation of the pressure plate. Steeling myself to put the car back up on jacks and see what's going on there.
 

Dirty Rick

Active member
Joined
Apr 10, 2013
Location
Cornholio, OR
Measure the plug wires with an Ohmmeter.
They can look new and be very high resistance.
You should not run any wires over 50k or under 5k with electronic ignition.
 

PNW760

Member
Joined
Jul 8, 2015
Location
Battle Ground, WA
The most interesting development is the maf. Twice on a test drive the car really bogged down, bucking in all gears and almost stalling in neutral. Pulled the plug to the maf during idle and it kept running, so I swapped in the old 016 maf. Idle came back, car now pulls harder than it ever has and the afr's haven't gone above 15. Could this have been a faulty 012 maf the whole time?

Yes. MAF is always the first thing to check in my opinion.
 
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