1994 SB TBI pulse msec (rich)

[Nitrousbob]

I am working on a friends rig for his daughter, It is running rich and fouling plugs like crazy.

I have checked the map sensor on the bench against a known good one, the coolant sensor, tested the fuel pressure (11-12psi), put in new plugs and gapped them (fouled again), got timing at 0deg with the wire disconnected, checked the coil windings, tried a new coil, cleaned grounds on the 3 connections up front, and cleaned up where the coil mounts.

Checked the Tps

got a Pulse of around 64.2msec at 860rpm, my Map sensor (only in the scan tool says 30Hg) which would be way off, but I would expect it to run lean at that point, It measured good voltage vs vacuum verified off the rig and running on the rig, I need to revisit that, it was in open loop. I would like to check the open time of the injector though, I just cant find info on the time, i can measure it but Im not sure.

I was wondering what the Pulse width is if anyone has that in a scan so I can check that, it will foul the plugs within seconds.

I pulled all the plugs and before I put the new ones in I verified that they all fired. Kinda yellow though.

My next try is to verify the spark power with a spark gap tester as I think its just not firing.

I tried unplugging the map sensor so it will go off RPM and tps as it said in the manual but I just want to verify the msec the injector is on, then I think im chasing an airflow in or out of the engine issue.

 

[pressureangle]

Here's mine for my built 400.

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[Schurkey]

Why is the MAP sensor showing atmospheric pressure when the engine is idling? Should be showing substantial vacuum (pressure reduction).

I'd expect to see 10--15 inches Hg not 30. Failed vacuum hose? Plugged vacuum port? Fix that, see what happens.

O2 sensor showing (False?) lean mixture, and zero cross-counts. Massive misfire?

 

[Nitrousbob]

Thanks yall, and the o2 I didnt pay much attention too yet because it was in open loop, it is definitely a false lean according to that picture, but I do remember looking at the scan tool and seeing it say rich when It was running so I will recheck, I logged it while it was running and I need to revisit that, I have a new o2 sensor sitting on my box if I get to that point, I just wanted to verify some other things first, Im going to make sure the balancer hasnt got out of sync if thats possible, the sensors are all plugged in and I back probed them while at amosphere and running, same with coolant temp cold and warm.

 

[tayto]

if map is reading atmosphere, you expect it to be lean? huh? when you are WOT you are atmosphere/near atmosphere so it would be adding fuel. i think you need to figure why your map isn't reading. do you have it hooked up to manifold vacuum source? check for 5v reference and return (ground). then check that the signal wire is making its way back to the ECM connector

 

[Nitrousbob]

So I just wanted to stress checking the mechanical as much as the sensors and what not. I ended up having a blown head gasket on the rig, that caused odd manifold vacuum and o2 readings, along with it misfiring, a quick compression test and a scope inside the cylinder. thanks for the insight on the platform, everything was runnin correctly on the ecu, the damn air pump was bad in one hole.

 

[Scooterwrench]

Why is the MAP sensor showing atmospheric pressure when the engine is idling? Should be showing substantial vacuum (pressure reduction).

I'd expect to see 10--15 inches Hg not 30. Failed vacuum hose? Plugged vacuum port? Fix that, see what happens.

O2 sensor showing (False?) lean mixture, and zero cross-counts. Massive misfire?

30Hg is not atmospheric pressure,it's total vacuum. 30kPa possibly?
30Hg would definitely create a lean out condition but that reading seems strange. As you said 10-15 Hg would be more the norm.

 

[Schurkey]

It's a Manifold Absolute PRESSURE (MAP) sensor, not a manifold absolute VACUUM sensor.

Old guys like me get confused. I sure was before I figured it out. It is sensing 30 inches of mercury of PRESSURE in the manifold. In other words, atmospheric pressure/barometric pressure just like a weather report, except that weather reports are all scientific-y now, so they have to be in crybaby Metric "Milibars" (remembering that one "Bar" is "one BARometric Pressure Unit", or about 29.5 in Hg.) Anyway, easy-to-remember round numbers: a bit more than 1000 mB or about 30 inHg of pressure is "no vacuum at all" depending on weather and altitude.

A vacuum gauge like I'm used to is calibrated "backwards", where "0" is atmospheric pressure, and the loss of pressure (vacuum) makes the needle move up-scale to 30 inches of mercury vacuum, which would be near-total vacuum, again depending on weather and altitude.

Pressure sensor starts at 30 inHG, more vacuum drops the reading until it shows "0" pressure.
Vacuum gauge starts at 0 vacuum, more vacuum increases the reading until it shows "30 inHg" "full vacuum".

Examples: (somewhat depending on weather and altitude)
10 inHg vacuum = 20 inHg pressure. 10 + 20 = 30
22 inHg vacuum = 8 inHg pressure. 22 + 8 = 30
8 inHg vacuum = 22 inHg pressure. 8 + 22 = 30

So a reading of 15-ish in/Hg is about the same with either pressure or vacuum, depending on gauge accuracy and today's weather. So seeing a reading of "15 in Hg" makes sense for either pressure or vacuum, and reinforced my (wrong) thinking that a MAP sensor was measuring vacuum.

 

[Scooterwrench]

Oh boy,I'm gonna have to learn a whole new vocabulary to mess with these modern rides.
OK so his MAP reading is engine not running or WOT.

 

[Schurkey]

got a Pulse of around 64.2msec at 860rpm, my Map sensor (only in the scan tool says 30Hg)

everything was runnin correctly on the ecu, the damn air pump was bad in one hole.

Oh boy,I'm gonna have to learn a whole new vocabulary to mess with these modern rides.

I certainly had problems even after I got working with a scan tool. This--pressure vs. vacuum--screwed me up for the longest time.

OK so his MAP reading is engine not running or WOT.

Best I can tell, his 30 inHg reading was at 860 rpm idle.

Yet he claims that the only problem was the head gasket.

I don't understand. Could the engine run so bad that there was no manifold vacuum at idle?