odd problem

[ggenovez]

Hi all,

I've been having an odd problem. Everything was running fine, when all of a sudden the fuel pump went.

Replaced the pump, and she had trouble starting. Pump PSI was 13. Noticed the spark plug was weak. Replaced the coil. And she started but ran rough. Ok. Timing. Disconnect the bypass and she was running ok but odd, Set her to 0. Put her on the road, and when I give her a little romp she stutters and wants to die. Thinking I the timing might have moved, I unplug the bypass and she stalls.

Ok, new plugs, wires, cap, distributor. Same problem. Won't idle with the bypass disconnected. OK. EGR. I made a plate and plugged it. Same problem.

I know what you're thinking. ignition module. Last year she died in Tennessee, and had her towed to a shop, where they told me the distributor had a bad ground. So they replaced the complete distributor. But just to put a stake through it, I took the old working ignition module from the old distributor, and swapped them, and she's still running the same.

I'm stumped.

Any ideas?

[Bill usn-1]

What system and what distr are you running?
I can only assume you have a SBC with a factory TBI.

I would definately suspect the timing circuit.
Have you set TDC and then verified the rotor is pointing at the cap terminal and reluctor is lined up?

Then without moving the distr the timing should be 0* with the bypass open.

Then turn off and connect bypass.
What is the timing at warm idle?

Do the checks below.
When you get to the module, swapping one in doesn't mean it was good if your old distr had a bad ground.

Take them in to the parts store and have them tested at least 3 times each.

Are you sure the pump was bad? If the ECM doesn't see a timing signal it won't turn on the fuel pump!!

Fuel Injected Engines

See Figure 1

Tag and disconnect the distributor lead and wiring from the coil.
Connect an ohmmeter as shown in Step 1 of the accompanying illustration. Place the ohmmeter on the high scale. The reading should be infinite.







Fig. Fig. 1: Fuel injected engine ignition coil test

Connect an ohmmeter as shown in Step 2 of the same illustration. Place the ohmmeter on the low scale. The reading should be very low or zero. If not replace the coil.
Connect an ohmmeter as shown in Step 3 of the same illustration. Place the ohmmeter on the high scale. The meter should not read infinite. If it does replace the coil.
Connect the distributor lead and wiring.



PICK-UP COIL



See Figures 2, 3 and 4

To test the pick-up coil, first disconnect the white and green module leads. Set the ohmmeter on the high scale and connect it between a ground and either the white or green lead. Any resistance measurement less than infinity requires replacement of the pick-up coil.







Fig. Fig. 2: The pick-up coil is located inside the distributor






Fig. Fig. 3: Testing the pick-up coil-coil-in-cap






Fig. Fig. 4: Testing the pick-up coil-separate coil

Pick-up coil continuity is tested by connecting the ohmmeter (on low range) between the white and green leads. Normal resistance is between 500 and 1500 ohms. Move the vacuum advance arm while performing this test. This will detect any break in coil continuity. Such a condition can cause intermittent misfiring. Replace the pick-up coil if the reading is outside the specified limits.
If no defects have been found at this time, and you still have a problem, then the module will have to be checked. If you do not have access to a module tester, the only possible alternative is a substitution test. If the module fails the substitution test, replace it.


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[ggenovez]

Yeah, I have a GM 350 TBI...

Yes. TDC and the timing mark/rotor align

She won't start or idle with the bypass disconnected.

With the bypass connected, warmed up she's at ~20' and steady.

Pickup coil and ignition coil check out.

Ignition modules, one check out fine the other did not. Still the same problem with either one.

Yeah Pump was bad. the fuse pump was popping.

I appreciate your help... Thanks

[Bill usn-1]

Does the timing move when you rev the rpm?
Did you check the timing when cranking?

Have you shined a timing light on the injectors to watch them when running.
You should have a nice cone pattern from both.

Do you have a check engine light?
Have you connected pin A and B of the ALDL connector to check for codes?
You will probably have to clear the codes and then run it again to get valid codes.

[Bill usn-1]

Just in case you haven't checked the basics.
Here's the voltage check sheet.

Something else to keep in mind is, if it won't run with the bypass open, the only thing the ecm is provinding is fuel.
So if it's running and you unplug the bypass, does the fuel stop? Do the injectors stop spraying?
If so then you need to check the wiring between the distr and the ECM.

[ggenovez]

Bill,

The timing increases but is steady as the RPMS increase (no bouncing)

The injectors are now fine. One was dribbling and I replaced it.

The only code I get is a code 33 but I think it's due to the stalling.

No, when I disconnect the bypass, the RPMs drop drastically, but the injectors are still firing, and will idle for 2-3 seconds before she stalls.

[Bill usn-1]

33 MAP sensor voltage too high (> 4.00 v). Possible vacuum leak to sensor or faulty sensor

You should check this.
Is the map mounted lower then the throttle body?
The code will not set due to stalling.

[ggenovez]

Ok. I'll have a look.

The MAP sensor is above the tbi.

I was thinking that since the pedal is depressed @ 1/2 way, and the RPM is low, and vacuum is non existent, then it would throw a MAP error

[Bill usn-1]

If you have a vacuum brake bleeder you should be able to use the specs listed in the parts required FAQ to test it.

Normally the code is set due to a closed throttle but a high map with the engine running.

I don't think all your running problems are the map sensor but it needs checked.

Once it's fixed then I would do the key on and engine running voltage checks.
If you had a data cable and laptop then logging data would be good.

CODE 33
Trouble Code 33 indicates that the Manifold Absolute Pressure (MAP) sensor is detecting unusually low vacuum in the manifold. Code 33 will get set when:
No Code 21 or Code 22.
Engine running.
Manifold pressure greater than 74 kPa (A/C "OFF") 83.4 kPa (A/C "ON.")
Throttle angle less than 2%.
Conditions met for 4.8 seconds.

Possible causes include:
1. Faulty MAP-to-ECM connection
2. Plugged or leaking sensor vacuum hose
3. Defective MAP sensor
4. Defective ECM

[ggenovez]

Hey Bill,

I got 5 V on Ref and 4.8 with the key on, and lost about 1 V / 5" of vacuum. No bleeding.

Any other ideas?

You mentioned you didn't beleive it was the MAP sensor. What's your guess?