Poor running

[arf3rn]

1990 with 67k miles. Started having this little warble out the exhaust and occasional back fire when cold. When gets warm (closed loop I assume) runs like garbage. Dies. Won?t start till cools off. Paper clipped the code reader and got H-42. Anyone have this issue before? Thanks.

[secondchance]

https://www.zr1.net/forum/showthread.php?t=27718

At least for Bill, H42 was caused by low voltage at battery.
Based on my experience from way back when, did you check vacuum line from MAP sensor to the back of the plenum?

https://www.jerrysgaskets.com/hose-map-sensor-vacuum-new-90-95-13d4/

[arf3rn]

I did. Even put a new on in case I couldn?t see an issue. Still puzzled.

[secondchance]

Assuming you are new to ZR-1 (and you may not be), a lot of LT5s ended up with leaky injectors due to OEM injectors not fairing too well with ethanol found in gasoline.
Has the car run poorly since you got it? Was it running fine until recently? Some back ground info may be helpful.

[arf3rn]

Been running like a champ. Per history and receipts it got new injectors at 57k miles - was about 15 years ago and 10k miles. Car got less than 800 miles on it in 12 years. I got it last May and have put 2k on it so far. Would have more but for the last month been fighting this issue.
Put fuel pressure gauge on it last weekend and it looked good.

[RSLyrick]

Code 42 (ECM code) is supposed to be related to the ignition mechanism (DIS / ECM)

See the pages attached.

The DIS and the ECM interact with each other over a set of 4 signal lines (+GND) :

- The crankshaft signal (for engine position and RPM, provided by the DIS to the ECM)
- The Bypass line (ECM applies 5V to this line to tell the DIS that it is now in charge of timing management, after reaching 400 RPM)
- the EST line (which is a modulated signal provided by the ECM containing the timing information to be used by the DIS, a signal transition from high to low tells that the next coil has to fire. This transition happens sooner or later to adjust timing).
- The fault line reporting the following errors :

1) The ignition module detects an EST fault input on CKT 423 (EST).
2) The DIS fault input CKT 900 to the ECM is open (poor connection/connector pin).
3) The DIS fault line is shorted to system ground (pinched wire).

Code 42 appears if there is a short or an open on the Bypass line or / and the EST line. This automatically forces the DIS to run back on its own timing table (engine running then poorly) like it does below 400 RPM, instead of using ECM timing data.

So code 42 can be triggered by the following things :

- connection between ECM and DIS for the Bypass / EST line is open or shorted.
- The connectors are not properly plugged into the DIS or the ECM.
- The electrical interfaces managing the Bypass Line and the EST line are faulty (receiving interface for the DIS, transmitting interface of the ECM).

If your engine is starting fine, running fine for a while and get suddenly code 42, it could be the ECM / DIS warming up, having weak solder joints at the connector which open / close with temperature cycling.

There is a diagnostic connector for the DIS link. Insert an oscilloscope probe into port C (EST signal) and E (Bypass signal) referenced to a clean ground and look for a sudden change in the behaviour.

Below 400 RPM :

- EST (Port C) < 1.3V.
- Bypass (Port E) around 0V.

Above 400 RPM (running):

- EST (Port C) < alternating between 5V and 0V (everytime there is a transition from high to low, a coil will fire). It is, somehow, a frequency modulated signal.
- Bypass (Port E) around 5V.

The smart thing about this DIS module is that it outputs the crankshaft signal to the ECM and monitor the EST signal send by the ECM at the same time. If somehow, there is transition from high to low that don't make any sense in regard to the cranshaft signal (engine position), it knows that something is wrong.

A faulty crankshaft sensor could (with low chance) lead to Code 42 but I don't see the correlation with the engine warming up...

[tccrab]

My vote is on the Map sensor hose.
Check it first, then see if the Code 42 comes back.

'Crabs

[arf3rn]

My thought too. Changed it out with a new one from Jerry?s Gaskets. No change.

[secondchance]

May be disconnect map sensor hose and start the car. If no difference, may be MAP sensor gone bad.
You shorted the ALDL into diagnostic mode and after flashing ?12?, no more codes. Right?

[arf3rn]

I did clear it. I can?t remember what the process was. I pressed eng/met or trip/odo or one of those buttons on the dash.

[secondchance]

Haven?t done it for awhile but clearing code, I believe, involves disconnecting the battery for a couple of minutes.
Hitting metric button and gauge button is for clearing oil change reminder light.

[RSLyrick]

Just a quick question. Why are we talking about a possible MAP issue here (vaccum or sensor itself) when he said that he got a Code 42 ?

How does the a MAP issue correlate with a possible ignition control issue ?

Just trying to understand the situation here...maybe I don't get the full picture and some of you got the same issue in the past and it was related to the MAP..?

[arf3rn]

I have never been a good diagnostician. I?ve always been kind of a parts changer. I just learned about open and closed loop and that?s what I?m curious about. It runs pretty decently cold, which I assume is open Loop and then begins running like garbage and that?s when it dies abs is hard to start again. I would think that was closed the loop.Not sure if that is somehow a factor.

[RSLyrick]

Understood, mass part changing is usually the only option on older vehicule when there's no computer to throw you codes and you don't have experience with engine malfunction.

In your situation, you got lucky and got a code 42 (assuming, you pull the right code ?). Then, there's a chance for you to pin point the issue.

Questions :

- After clearing the code and starting the car, does code 42 come back again ? (you got a H42 = History Code 42 = Intermittent issue, not a constant issue like a C42).

- If yes, when the Service Engine Soon light comes up, does it happen as the same time as the engine start running rough or do you even get it when the engine is running OK ?

[arf3rn]

I?m gonna try to nurse it out tomorrow and see if it throws another code. I?m pretty certain I cleared it last weekend. Tricky part is the engine light does not come on. It was on an a couple weeks ago and showed an O2 sensor and I replaced those. Did find a cut black wire on the passenger side. Cleared the engine light and it has yet to come back on. I did learn that the second set of injectors do not come on when the check engine lights on.

[viper107]

ecm are horrible early years,may want to look into that also

[Macroblock]

Could be related to the crankshaft sensor, injectors and/or Engine Computer (ECM).

Code 42 means the ECM is in Bypass Mode, during which spark-timing is controlled by the DIS and not the ECM. This makes me suspect an ECM issue.

Here's a step-by-step guide to help with diagnosis:
https://www.zr1ecm.com/youfix.html

[arf3rn]

Thank You. I haven?t had a chance to mess with it - Prob be next week before I can start on it. Thanks for the link.

[A26B]

Just read this post.
For the time being, I suggest setting aside the Code 42 issue and check something else that is much simpler and a frequent cause of the symptom you describe.

Fuel Pressure: Yes, you checked fuel pressure. I am going to assume you checked fuel pressure when engine was cold (i.e. open loop), key on, engine off. There is no mention of isolating the primary & secondary pumps to verify BOTH pumps are functioning properly. Without isolating each pump, you could have a bad primary pump & not know it.

For a cold start, both FP1 & FP2 will run until the engine reaches appx 176F, then FP2 will shut off. For a hot start, above 176F, both FP1 & FP2 will run, but after 2 sec, FP2 will shut off.

The procedure to check fuel pumps is as follows;

Cold Engine
Key off, Engine off
Attach Fuel pressure gauge line to fuel rail. Bleed down any pressure in the rail.

Testing FP1 (Primary Fuel Pump)

1. Remove FP2 fuse.

2. Turn Key on, Engine off.

3. Observe fuel pressure. Should be appx 45 psig

4. Key off, engine off.

5. Bleed down fuel pressure

Testing FP2 (Secondary Fuel Pump)

1. Replace FP2 fuse and remove FP1 fuse

2. Turn Key on, Engine off.

3. Observe fuel pressure. Should be appx 45 psig

4. Key off, engine off.

5. Bleed down fuel pressure

6. Replace FP1 fuse.

[arf3rn]

Part of my diagnosing was to pull the fuel pumps and replace them with the new single pump system.

[A26B]

Part of my diagnosing was to pull the fuel pumps and replace them with the new single pump system.

So you did that and the problem still persists?

[arf3rn]

Yes Sir. That and new plugs, checked fire, map sensor hose, new vacuum assembly/hose that houses the ECV valves and new ECV valves. Problem started about 100 miles after that exchange. Pulled it all off and checked and put it all back on just in case. No changes.