Engine misses, stumbles, coughs - undriveable

MichBC3

Member
Bought a modified '87 GN 2 years ago with plans to do more upgrades over time. It ran fine for about a year, then a problem came up out of nowhere. Iin Feb '19, I was doing an easy 45 mph cruise after fueling up at a gas station. After 2 miles, the engine started missing very badly. A/F went rich: 10 to 1. Fuel pressure was ok = 38 psi. But the car wouldn't go faster than 30 mph. Barely got it home. Engine ran bad whether warmed up or cold (note: cold here in FL is 75+ degrees).

Drained and refilled the gas tank - twice. No difference. Upgraded to a new fuel pump, regulator & larger return line, set FP at 43 vac line off. No change. Tried swapping ignition module and coil pack. No change. Tried a different MAF. No change. Tried different MAP. No change. Tried different crank sensor. No change. Changed to a different ECM (& transferred TT chip). No change. Powerlogger is working: displays rpm, temp sensor and MAP readings. No trouble codes displayed on the Scanmaster. Pulled plugs - all 6 covered in thick black, wet deposits.

I parked the car and built an entirely new engine (forged parts & roller cam) - just completed. To break in rings, wanted to run engine for 10 minutes at 2600 rpm. After 6 minutes it missed, then missed more as time went on. Pulled plugs. Lots of black, wet carbon deposits - just like in '19. Exhaust spit out black soot. Bosch O2 sensor is new.

What other info do you need to figure this out?

TT alky chip & Motron 60 lb/hr injector combo
Powerlogger
Scanmaster 2.2
Bosch 13953 3 wire-narrow band O2
62 Precision turbo
Razor Alky Control
Front mount intercooler
212 Crane hydraulic roller cam
Fuel 93 octane gasoline
Innovate Wideband gauge
Autometer Fuel pressure gauge
Caspers knock gauge
Autometer boost/vacuum gauge
Autometer tachometer
 

Attachments

  • Exhaust.jpg
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ScottHeidinger

Active Member
I would take a look inside the intake plumbing after the turbo. Maybe the seal in the turbo is bad and leaking oil into the intake but I would think you would have seen this during the swap. There is also a aftermarket hot wire kit for the ignition module that some of us have used because of issues with the factory wiring.


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blackazz

Not a Gn
X2 on the cam sensor.did the little tab brake from the ring.
Pull the cam cap an give the brass looking cup a spin by hand, if it spins you need a new cam sensor or rebuild

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MichBC3

Member
New plug wires?
Cam Sensor?
Plug wires are like new (at least externally). They are 9 mm. I've have had the plugs in and out several times to clean off carbon deposits. If it was wires, I'd think that there would have been a noticeable change. I installed the cam sensor and set the position very carefully using the Casper's electronic tool. Worked fine. But thanks for trying! All input appreciated.
 

MichBC3

Member
I would take a look inside the intake plumbing after the turbo. Maybe the seal in the turbo is bad and leaking oil into the intake but I would think you would have seen this during the swap. There is also a aftermarket hot wire kit for the ignition module that some of us have used because of issues with the factory wiring.


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You may be on to something there. I noticed some oil in the upper plenum that I thought might be coming from the PCV. I may have to yank that turbo and get it checked. I have done just about everything else... thank you.
 

MichBC3

Member
X2 on the cam sensor.did the little tab brake from the ring.
Pull the cam cap an give the brass looking cup a spin by hand, if it spins you need a new cam sensor or rebuild

Sent from my SM-G965U using Tapatalk
When I installed the cam sensor, the window ring was tight to the shaft and gear - no play. Probably not the issue.
 

MichBC3

Member
I would take a look inside the intake plumbing after the turbo. Maybe the seal in the turbo is bad and leaking oil into the intake but I would think you would have seen this during the swap. There is also a aftermarket hot wire kit for the ignition module that some of us have used because of issues with the factory wiring.


Sent from my iPhone using Tapatalk
On second thought, the intercooler plumbing was clean and dry. Also, the A/F is very rich. So a turbo oil seal probably isn't it. I am now in contact with Eric at Turbo Tweak. He offered to test the chip. Probably that's my next move.
 

ScottHeidinger

Active Member
I think you were using a different screen name then. You have my email address or I can send it to you. If you can send me a power logger file with it missing maybe I can see something in the file that will help.


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Buckshot G/N

Well-Known Member
Sounds as if you have diagnosed most elements. But as you well know these cars will make you gray headed quickly. If Scott can can't find a solution on the read out. I would consider having it tolled up to Don Cruz Performance in Tampa. ? Good Luck.
 

Chuck Leeper

Toxic old bastard
Staff member
Exh leaks?
Bad grounds?
Start and unplug cam sensor?
Volt drop tests?
Tried "adjusting" the cam sensor?
 

MichBC3

Member
I think you were using a different screen name then. You have my email address or I can send it to you. If you can send me a power logger file with it missing maybe I can see something in the file that will help.


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Just made a Power Logger file. Though my wideband gauge only reads as low as 10 to 1, the PL log says it's more like 7 to 1. I just sent it to Eric at TurboTweak for analysis and comment, but I will attach it for you to see Scott. Bob
 

Attachments

  • PL 5-27-20 a.dat
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MichBC3

Member
Exh leaks?
Bad grounds?
Start and unplug cam sensor?
Volt drop tests?
Tried "adjusting" the cam sensor?
Hi Chuck - This is a recently assembled engine so no exhaust leaks. Checked grounds several times (especially the 4 at the rear of the intake manifold on the passenger side. This same missing/rich issue started when I was using the previous engine. I already tried changing the cam sensor back then. No difference. I set the camshaft sensor very carefully using the Casper's electronic tool (22 ATDC) on my degreed BHJ balancer when I built this new motor. Remember, that this problem originally started in the previous engine right in the middle of an easy cruise. So the cam sensor would have to have done something wacky in the same manner. When I had the cam sensor in my hand, there was nothing weird about it. I'm not sure which volt drop tests you are referring to but the power logger data log that I just made shows all voltages healthy (TPS correct, battery voltage 14). I am beginning to suspect the chip. So am working on that.
 
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