Hey Everyone,
I have an interesting problem with my '88 3800 with 126K miles. I was travelling and stopped for a short time. Up to this point,
I had no problems. When I went to start, the motor cranked fine, but no start. I replaced the coil pack and ignition module as I know
these have a history. Started and drove 700 miles home without incident. Stopping for fuel and food. No problem.

The next day, I was unable to start. Same symptom. Put fuel pressure gauge on fuel rail and measured steady 44 lbs.
Left gauge on for another half hour and no drop in pressure. Fuel pump is good.

Next pulled spark plug wire and plugged in spare plug to check for spark. No problem. White color.

Hmm, I have fuel and spark. I visually checked the cam and crank sensors to make sure of no visual damage. Unplugged the connectors and looked
fine. No problem. Reconnected.

Squirt starting fluid in intake and it started. Ran fine for 10 minutes with no stumbling or other issues. I did notice the fast idle was abnormally high (2000).
Turned off and tried to restart. No start. Waited an hour with still no start. I'm confident I could drive it several hundred miles without problem....until I turned it off.

Any ideas? TPS (throttle position sensor)?

Thanks for any ideas.......Larry

Hey Everyone,
I've got a '88 3800 with 126K miles that refused to start recently. It had no symptoms previously and cranks freely with no start.
I'd guess it'* been >50K miles since last clearing of the codes. The first time the no-start happened, I replaced the coil packs and
associated ignition control module. It was good for a week, but then refused to start once again.

Checked OBD codes and this is what was stored.
DTC - 21 Throttle Position sensor error (signal high)
DTC - 24 Vehicle speed sensor error (open circuit or no activity)
DTC - 26 Quad Driver Module (QDM A) error (this code has always been present and have no idea where to start)
DTC - 28 Auto transmission range pressure switch error
DTC - 31 Wastegate solenoid circuit error
DTC - 39 TCC error
DTC - 42 Ignition bypass circuit error
DTC - 64 Right bank O2 sensor lean exhaust indicated

Disconnected ground cable to clear codes.

Note that no codes were thrown during the following tests.

Fuel - Spark - Air

Fuel - Installed fuel pressure gauge on fuel rail shrader valve and read a steady 44lbs while cranking. Left there for extended time with no loss of pressure. Not a fuel delivery problem.

Spark - Visually inspected both cam and crank sensor for damage. None seen. Un-plugged connectors and reconnected. Plugged spare spark plug into wire and observed while cranking. Good white spark. No a spark problem.

Air - Disconnected intake snorkel and sprayed in starter fluid. Engine started and ran for 10 mins with no stumbling or roughness. Turned off key and tried to restart. Would not start.

I'm now focusing on the intake system and associated parts (TPS, MAF, butterfly valve, etc.).

Thoughts before I start shot-gunning parts?

Thanks in advance,
Larry

My first thought is that the Crank Position sensor is messing with you.

Their 'typical' symptoms are failed hot restarts. Once the CPS cools off, it will start just fine. They also never set codes in the process.

CPS can usually be confirmed by no tach signal during cranking in the fault condition, and if you hit it with water when hot to cool it off, it will restart.

TPS will usually trip a fault code if it'* bad enough, so will most other things.

Speaking of which, are there any codes?

Codes can mean different things with different cars.

When I look at a list targeted at the LN3, this is how it'* looking:
https://www.troublecodes.net/gm/88-90_38c/

21TPS voltage was above 0.8 volts for 5 seconds when engine was running and air flow was less than 15 gm/sec, or the TPS voltage was over 4.8 volts at any time.
24 Vehicle speed sensor signal showed less than 3 MPH for 40 seconds when vehicle was in 4th gear.
26 Quad-Driver sense voltage shows a low voltage when battery voltage should be present, or if the sense voltage shows battery voltage when a low voltage should be present for at least 5 seconds when the engine was running.
28 3rd gear switch was closed or grounded when vehicle was in 4th gear, or 3rd or 4th gear switch was open when engine was first started.
31 Park/Neutral switch was grounded when vehicle was in gear, or Park/Neutral switch was open when vehicle was first started, or the 4th gear switch has an intermittent open.
39 Not listed
42 The EST signal did not change when the ECM applied bypass voltage to the ignition module.
64 Incorrect EGR operation.

If you clear codes and attempt to start, what codes set immediately?

Threads merged, please don't start multiple posts about the same issue.

Yes, I agree with the guys........

A bad crank sensor could be the problem.......if you can get the car to start and run, do this test:

FIRST, PRACTICE!!!!!!!!!!!!!!!!

With a long extension, PRACTICE tapping the PEDESTAL, of the crank sensor, NOT the crank sensor itself......

You want to practice, because that serp belt will be moving and you don't want to catch the bar in belt....

With the car at normal operating temp, tap the pedestal lightly, a couple times......if the car dies, or if it stumbles, you need a crank sensor.....

What happens is, sometime the crank sensor is not putting out a "square wave"......as they get older the edges tend to round off, and the ICM may have trouble interpreting the signal.....

This test is not foolproof...nothing may happen, and it could still be the crank sensor......

I also agree, that you should clear the codes and run the vehicle to see which codes come back......if all of them do, I am thinking ECM.....access the ECM.....have someone run the car until normal operating temp is achieved, apply brake, and put in D, and rev to 1500 rpms.....then with the palm of your hand , tap the top of the ECM(not the bottom)......the top has the access cover for the PROM.......don't do this for more than 15 seconds......if the car stumbles/dies, you need an ECM....once again, this is not a foolproof test, nothing may happen and it could still be the ECM.....

Thanks for the suggestions..........

The problem was a burnt TPS connector that had fallen onto the crossover header at some point. Since the TPS header is under the throttle body, I was not able to see
it until I blindly disconnected it. I wasn't sure if this was the problem but it was obvious the connector needed to be replaced. I believe the connector had been
damaged years ago before I bought the car. When reading the manual about the TPS, the voltages involved ( .33 and .46v) makes the connection integrity
important.

I ordered and replaced the connector and it started right up. I've driven a half dozen times and starts every time. I believe that was the problem. It never did
throw codes.