1988 Starts and Immediately Dies

[pshaver8]

The car starts fine cold and runs for about 45-60 seconds then dies, if I try to restart it will fire and run for another 5-10 seconds before dying again. I can try and restart a bunch of times and it will fire and run each time for about 5 seconds. If I let the car sit a while (1/2 hour or more) it will again run perfect for almost a minute before dying. Throughout all of this the car is not throwing any check engine light codes either.

What I have done so far is check the resistance across the injectors both cold and immediately after it starts acting up (both time all 8 were very close to 16 ohms, within +/-.2), I checked the fuel pressure throughout the run and restart process (holds 40-45psi at all times), and I tested the pickup coil on top of the distributor both cold and after it starts acting up per the FSM and it tested good. I also replaced the module under the rotor in the distributor (after the auto store guy suggested this was the problem) but it made no difference.

If I unplug the MAF sensor after it starts acting up it will run and stay running indefinitely. I believe that pulling the MAF out of the loop forces the ECM to run on a MAP, but my question is does anyone know what sensors run on the same loop as the MAP so I can begin testing them? Or any advice on what it could be, the MAF sensor is new and when that went out last summer it threw a check engine light code so I'm thinking that is not the problem, but I've been told the TPS, O2 sensors, or a bad ground could be suspect.

Thanks in advance to any help and or advice.

Patrick

 

[John Robinson]

Welcome to the forum. From what you say it sounds like when you remove the MAF and it runs it is going into the limp home mode. Try researching the FSM for the section that tells what the ECM does to get it into limp home mode. It should tell you what it bypassed to make it run and that might lead you to the system that is not working.

Two other things to check. A broken wire is a possibility. Check the grounds and clean them. It all goes back to the ECM needing a good signal from each sensor to adjust the engine to run. It seems that with the age our cars are getting they are becoming more and more sensitive to decaying wires and dirty grounds. The parts stores are making a fortune on selling sensors that are not needed. Even if you get a code it only tells you that something is wrong on that circuit it does not tell you the sensor is bad.

 

[WhalePirot]

Hmmmm Was thinking oil pressure switch or relay for the fuel pump initially, until you said disconnected MAF allows it to run.

How about cleaning it with carb cleaner, carefully, and checking for disconnected wires. I don't have my FSM handy to see how to test it.. sorry.

Very true, what John said about these computer controller cars needing good electrical contacts, unlike the old days. I have fixed countless things by either cleaning contacts, grounds or fixing broken wires, on the Vette and old Volvo and a BWM. (Also why I don't high pressure wash the engines.) I doubt the last three sensors caused a sudden quitting problem, esp in light of your MAF 'fix'.

 

[Kettsvette]

RE:1988 Starts and dies

The car starts fine cold and runs for about 45-60 seconds then dies, if I try to restart it will fire and run for another 5-10 seconds before dying again. I can try and restart a bunch of times and it will fire and run each time for about 5 seconds. If I let the car sit a while (1/2 hour or more) it will again run perfect for almost a minute before dying. Throughout all of this the car is not throwing any check engine light codes either.

What I have done so far is check the resistance across the injectors both cold and immediately after it starts acting up (both time all 8 were very close to 16 ohms, within +/-.2), I checked the fuel pressure throughout the run and restart process (holds 40-45psi at all times), and I tested the pickup coil on top of the distributor both cold and after it starts acting up per the FSM and it tested good. I also replaced the module under the rotor in the distributor (after the auto store guy suggested this was the problem) but it made no difference.

If I unplug the MAF sensor after it starts acting up it will run and stay running indefinitely. I believe that pulling the MAF out of the loop forces the ECM to run on a MAP, but my question is does anyone know what sensors run on the same loop as the MAP so I can begin testing them? Or any advice on what it could be, the MAF sensor is new and when that went out last summer it threw a check engine light code so I'm thinking that is not the problem, but I've been told the TPS, O2 sensors, or a bad ground could be suspect.

Thanks in advance to any help and or advice.

Patrick

What ended up being the problem and what was done to fix it. I have a similar problem and this could save a lot of time.

 

[vigman]

Patrick

Will the car restart after it dies ( maf connected ) and you use a blast of quickstart?

Mike

 

[John Robinson]

Welcome to the Forum. Vigman question is very important. I am attaching a couple of documents that may show you how very tricky these cars are to all the sensors. Note that different sysstems are used at different times by the ECM. Doing something like disconnecting the map or maf sensor will cause the ECM to ignore some circuits and to use others to determine engine needs.

DRIVEABILITY AND EMISSIONS S.7L (VIN P) 6E3-A-19
TYPICAL TeCH 1 DATA DEFINITIONS
ECM DATA DESCRIPTION
A list of explanations for each data message
displayed on the Tech 1 scan tool begins below.
This information will assist in tracking down
emission or drivability problems, since the displays
can be viewed while the vehicle is being driven. See
the "On-Board Diagnostic (OBO) System Check" for
additional information.
With the Tech
1connected, the ASR system may
be disabled and the "Service ASR" light may turn
"ON."
ENGINE SPEED - Range 0-9999 RPM -
Engine speed is
computed by the ECM from the distributor reference
input (low resolution circuit). It should remain close to
desired idle under various engine loads with engine
idling.
r:
DESIRED IDLE - Range 0-3187 RPM -
The idle speed
that is commanded by the ECM. The ECM will
compensate for various engine loads to keep the engine
at the desired speed.
ENG COOL TEMP - Range -40°C to 151°C, -40°F to 304°F
- The Engine Coolant Temperature (ECT) sensor is
mounted in the coolant pump and sends engine
temperature information to the ECM. The ECM
supplies 5 volts to the ECT sensor circuit. The sensor
is a thermistor which changes internal resistance as
temperature changes. When the sensor is cold
(internal resistance high), the ECM monitors a high
signal voltage which interprets it as a cold engine. As
the sensor warms (internal resistance decreases), the
voltage signal will decrease and the ECM will
interpret the lower voltage as a warm engine.
INTAKE AIR TEMP - Range -40°C to 196°C. -40°F to
38soF -
The ECM converts the resistance of the intake
air temperature sensor to degrees. Intake Air
Temperature (IAT) is used by the ECM to adjust fuel
delivery and spark timing according to incoming air
density.
MAP - Range 11-105 kPa/0.00-5.10 Volts -
The
Manifold Absolute Pressure (MAP) sensor measures
the change in the intake manifold pressure which
results from engine load and speed changes. As intake
manifold pressure increases, the air density in the
intake manifold also increases and additional fuel is
required.
BARO - Range 11-105 kPa/0.00-S.10 Volts -
The BARO
reading displayed is measured from the MAP sensor at
key "ON," engine "OFF" and WOT conditions. The
BARO reading displayed represents barometric
pressure and is used to compensate for altitude
differences.
THROT POSITION - Range 0-S.10 Volts -
Used by the
ECM to determine the amount of throttle demanded by
the driver. Should read .36-.96 volt at idle to above 4
volts at wide open throttle.
THROTTLE ANGLE - Range 0 - 100% -
Computed by the
ECM from TP sensor voltage (Throttle Position) and
should read 0% at idle and 100% at wide open throttle.
Refer to DTC 21 ifTP sensor angle is not 0% at idle.
OXYGEN SENSORS- Range 0-996 mV -
Represents the
exhaust oxygen sensor output voltage. Should
fluctuate constantly within a range between 10 mV
(lean exhaust) and 1000 mV (rich exhaust) when
operating in "Closed Loop."
lOOP STATUS - Tech 1 ~isplays Open or Closed -
"Closed Loop" displayed indicates that the ECM is
controlling fuel delivery according to oxygen sensor
voltage. In "Open Loop," the ECM ignores the oxygen
sensor voltage and bases the amount of fuel to be
delivered on TP sensor, engine coolant, and MAP
sensor inputs only.
SHORT TERM FUEL TRIM - Range 0-2SS -
Short term
fuel trim represents a short-term correction to fuel
delivery by the ECM in response to the amount of time
the oxygen sensor voltage spends above or below the
450 mV threshold. If the oxygen sensor voltage has
mainly remained below 450 mV, indicating a lean
air/fuel mixture, short term fuel trim will increase to
tell the ECM to add fuel.
If the oxygen sensor voltage
stays mainly above the threshold, the ECM will reduce
fuel delivery to compensate for the indicated rich
condition.
LONG TERM FUEL TRIM - Range 0-2SS -
Long term fuel
trim is derived from the short term fuel trim value and
is used for long-term correction of fuel delivery. A
value of 128 counts indicates that fuel delivery
requires no compensation to maintain a 14.7:1 air/fuel
ratio. A value below 128 counts means that the fuel
system is too rich and fuel delivery is being reduced
(decreased injector pulse width). A value above 128
counts indicates that a lean condition exists and the
ECM is compensating by adding fuel (increased
injector pulse width).


Hope this sheds some light on thetps for you

---

​

ThrottlePosition Sensor (TPS)
Copied from 1993 Service Manual​

The Throttle Position sensor (TPS)is a potentiometer connected to the throttle shaft on the throttle body. It isa potentiometer with one end connected to 5 volts
from the ECM and the other to ECM ground. A third wire is connected to the ECMto measure the voltage from the TP sensor. As the throttle valve angle ischanged (accelerator pedal moved), the voltage output of the TP sensor alsochanges. At a closed throttle position, the voltage output of the TP sensor islow (approximately .5 volt). As the throttle valve opens, the output voltageshould be approximately 5 volts.

By monitoring the output voltage from the TP sensor, the ECM can determine fueldelivery based on throttle valve angle (driver demand). A broken or loose TPsensor can cause intermittent burst of fuel from the injectors and cause anunstable idle, because the ECM detects the throttle is moving.

If the TP sensor circuit is open, the ECM will set a DTC 22. If the TP sensorcircuit is shorted a DTC 21 will be set. A problem in any of the TP sensorcircuits will set either a DTC 21 or 22. Once a DTC is set, the ECM will use adefault value for TP sensor, and some vehicle performance will return.

A personal note, when my TPS failed it DID NOT set a code other than totell me the ECM was bad.

Again your problem is to isolate which of the sensor circuits is not communicating to the ECM. Keep in mind the four sensors the ECM uses to determine fuel delivery etc are the TPS, MAP/MAF ,Water Temp and the O2 Sensor. Each of these sensors go to a common ground in the wiring harness and that if that ground is bad or if there is a broken wire to one of the sensors the ECM can only tell you the circuit for the sensor is bad a code does not mean the sensor is bad.

---

​

 

[vigman]

Other thoughts

When the car first fires ... run to the back and get a whiff of the exhaust ( no don't stick your nose in the pipe ) ... does it smell rich?
AND
What area do you live in... really cold... or Arizona.....? ( Never mind , your in Minnesota read ice station Zebra ) ....

So ECU temp senders will play a big part....

AND

Do you have an aftermarket air filter like a K&N ?
Is this an OUTSIDE car or a garage queen.... are there signs of rust in the engine bay frame rails ?

Mike

 

[Kettsvette]

When the car first fires ... run to the back and get a whiff of the exhaust ( no don't stick your nose in the pipe ) ... does it smell rich?
AND
What area do you live in... really cold... or Arizona.....? ( Never mind , your in Minnesota read ice station Zebra ) ....

So ECU temp senders will play a big part....

AND

Do you have an aftermarket air filter like a K&N ?
Is this an OUTSIDE car or a garage queen.... are there signs of rust in the engine bay frame rails ?

Mike

Thanks for the responses. I bought the car in April. I don't think it was driven much the last few years before I bought it but it seems to be going through a re-break-in period with the electrical system.

I had an earlier problem with the mileage range and MPG readouts from the instrument cluster that seemed to be intermitent. I checked as much wiring as I could see. The only thing I did was top off the battery cells with distrilled water even though they looked ok. This problem is still present but not as often. The battery is a year old. I live in Arizona so the summer heat could have contributed to this but I am not certain. The car stays in the garage for safety reasons but I drive it as much as I can. There are no signs of rust on the car anywhere so I am lucky in that regard.

Getting back to this start-stop problem, I did not try to restart the car for a few days due to business travel. However, once I got a chance, I checked all the wiring to and from the devices that were noted in the FSM that affect the TPS for obvious signs of degradation. I removed the connectors from the devices and reconnected them to make sure they made good contacts and were not broken. After all this, I tried to restart the engine and it started right up.

I had planned to check the codes today to see what read-out that may have contributed to the problem but the car wouldn't start at all. I again checked the battery wiring but the wiring to the negative side was not as tight as it should have been. Once I re-tightened the battery cable, the car started right up but there were no codes to work from.

Also, the air intake is stock with what looks like a Pfram air filter. I am planning to install an aftermarket venturi in front of the throttle that is supposed to add HP but it may be hype.

If the starting problem raises it's head again, I will refer back to this thread and perform the tests as suggested. Thanks for all the help and suggestions with this TPS problem.

 

[Schrade]

The car starts fine cold and runs for about 45-60 seconds then dies, if I try to restart it will fire and run for another 5-10 seconds before dying again. I can try and restart a bunch of times and it will fire and run each time for about 5 seconds. If I let the car sit a while (1/2 hour or more) it will again run perfect for almost a minute before dying. Throughout all of this the car is not throwing any check engine light codes either.

What I have done so far is check the resistance across the injectors both cold and immediately after it starts acting up (both time all 8 were very close to 16 ohms, within +/-.2), I checked the fuel pressure throughout the run and restart process (holds 40-45psi at all times), and I tested the pickup coil on top of the distributor both cold and after it starts acting up per the FSM and it tested good. I also replaced the module under the rotor in the distributor (after the auto store guy suggested this was the problem) but it made no difference.

If I unplug the MAF sensor after it starts acting up it will run and stay running indefinitely. I believe that pulling the MAF out of the loop forces the ECM to run on a MAP, but my question is does anyone know what sensors run on the same loop as the MAP so I can begin testing them? Or any advice on what it could be, the MAF sensor is new and when that went out last summer it threw a check engine light code so I'm thinking that is not the problem, but I've been told the TPS, O2 sensors, or a bad ground could be suspect.

Thanks in advance to any help and or advice.

Patrick

Sounds like you got a pretty good start on diags here, except for the "I've been told ... " part. Pay NO MIND to words. Words go away when the sound stops. Friend said that? Great; show me how YOU spent your money on car work, then I'll judge.

Cold start startup, and cold idle means nothing. NO THING.

Driving away from a repair shop in OPEN LOOP??? And NO SES light??? That means, Problem solved??? HaHaHaHaHaHa. Means the same as above (you got taken - biggest scammode there is - have it warmed up when I get there).

Dis-connecting stuff tells you the same as above - at best - NO THING. At worst, THE WRONG DIAGNOSIS (or NO DIAGNOSIS).

Whoever said 'Bad Ground', was dead on...

 

[John Robinson]

I hope you have fixed the problem. Just for something to do when it is running shake and move all the wires from the TPS, MAP etc that go in the wiring bundle. While doing that listen for the engine to change or quit running. If it does than start to follow the wires back into the large wiring harness until you find the large bundel of ground wires that are all connected together. If that bundle is corroded take the wires and seperate them and then do a continuity check back to the connector(DO NOT BACKPROBE TO THE ECM). That will verify they are not broken between the connector and the ground. Strip the wires to get new clean wire and reconnect them using solder. Finally recover the bundle with either electrical tape or use the liquid tape to cover them up. Now that you are already working on the car and the hood is up it is a good time to clean the rest of the grounds. The chart am showing you is from my 93 manual but you get the picture.

The important ones are the frame rails and the bell housing grounds since they are the ones for grounding the wiring for the engine. The grounds not in the engine bay are for electrical things like lights etc. I again hope you have solved your problem but if not this is the next step to follow. As for the grounds needing cleaning that is something that needs doing just like an oil change. Except this is every 10 years or so. Storage and moisture quickly seep into the grounds and they lose there effectiveness. The more you work on the car the more you will come to realize the grounds are the lifeblood of a Corvette.

 

[gmjunkie]

I hope you have fixed the problem. Just for something to do when it is running shake and move all the wires from the TPS, MAP etc that go in the wiring bundle. While doing that listen for the engine to change or quit running. If it does than start to follow the wires back into the large wiring harness until you find the large bundel of ground wires that are all connected together. If that bundle is corroded take the wires and seperate them and then do a continuity check back to the connector(DO NOT BACKPROBE TO THE ECM). That will verify they are not broken between the connector and the ground. Strip the wires to get new clean wire and reconnect them using solder. Finally recover the bundle with either electrical tape or use the liquid tape to cover them up. Now that you are already working on the car and the hood is up it is a good time to clean the rest of the grounds. The chart am showing you is from my 93 manual but you get the picture.

View attachment 11804
The important ones are the frame rails and the bell housing grounds since they are the ones for grounding the wiring for the engine. The grounds not in the engine bay are for electrical things like lights etc. I again hope you have solved your problem but if not this is the next step to follow. As for the grounds needing cleaning that is something that needs doing just like an oil change. Except this is every 10 years or so. Storage and moisture quickly seep into the grounds and they lose there effectiveness. The more you work on the car the more you will come to realize the grounds are the lifeblood of a Corvette.

 

[ronmeggs]

thx

tried what you said you tried and my MAF was bad fixed now best of luck on your car

 

[WhalePirot]

I removed the connectors from the devices and reconnected them to make sure they made good contacts and were not broken.

An excellent time to properly use contact cleaner on them.