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MAP Sensor replacement not solving engine issue


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#21 NotEnoughGPs

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Posted 10 December 2017 - 05:02 AM

There's a huge difference in diagnosis between "Won't Crank" and "Cranks but won't run".  Both involve the engine not starting.  Which is it?

 

 

 

 

How old are the spark plugs?

 

Agree:  This vehicle and a scan tool need to meet each other.

Yes, about the long winded description of mine, I need to clarify that this 2003 GTP has an "Engine cranks but won't start" condition. It won't start after the engine has been driven 15 miles or more.

The spark plugs and wires were changed out by the previous owner already. The is no CEL on, and the car starts up easily on a cold engine, so I don't suspect there is any issue with spark. 

I do plan to get a good scan tool on it, but I have to drive over 35 miles to have this done. Right now, I am hoping to fix the no-start condition by replacing vacuum hoses, and the catalytic converter, and the wiring leading to the MAP sensor.


Pontiac owner since 1999, driven over 500,000 actual miles in Grand Prix's I have owned

2001 Pontiac GTP, silver (31,000 miles) too many mods to list, currently in storage

2001 Pontiac GTP, silver (98,000 miles) small turbo, built tranny, currently in storage

2002 Pontiac GT, 40th Anniv, dark cherry (273,000 miles) mild mods, daily driver

2002 Pontiac GTP, red (58,000 miles) strictly driven to car shows, currently in storage

2003 Pontiac GTP, LE, blue/black (187,000 miles) all stock, daily driver


#22 NotEnoughGPs

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Posted 10 December 2017 - 05:14 AM

Agreed. Though if it comes to it, or anyone stumbles upon this thread needing to change the CPS, (I'll have to post a separate thread eventually about this) I bought three balancer pullers before I found this: 

 

https://www.autozone...r-gm/409642_0_0

 

They also rent these at all autozones. It works with the autozone loan tool balancer pullers and is the only rental tool that works to pull our pulley's at any of the local auto parts stores. 

 

Also as a quick tip for either A) those who don't like the starter trick to spin the balance bolt off or B) those who can't crank their car over at the time (aka have stuff off or junkyard) the easiest way I've found is taking a jack stand and taping a flat-blade screw driver to it and using this "tool" to rest against where the flywheel inspection cover goes and in the flywheel teeth. Don't worry, I've done this dozens of times and have not once damaged either the transmission housing, flywheel teeth, or the tool! This method works really well for installation as well!

 

Hope this helps someone and hopefully you don't have to replace yours. 

 

Again, post those codes!!!

From extensive reading on the CPS, I believe that it is not to blame for the no-start condition. The CPS does not get heatsoaked according to everything I have read. When a CPS is faulty, it can cause the engine to stop at any time. Also, I was asked to observe the RPM's on the tach when cranking. If the CPS is bad, then the tach will be sitting at zero . That is my understanding. 

As for a scan tool diagnosis, that is going to occur soon.


  • wstefan20 likes this

Pontiac owner since 1999, driven over 500,000 actual miles in Grand Prix's I have owned

2001 Pontiac GTP, silver (31,000 miles) too many mods to list, currently in storage

2001 Pontiac GTP, silver (98,000 miles) small turbo, built tranny, currently in storage

2002 Pontiac GT, 40th Anniv, dark cherry (273,000 miles) mild mods, daily driver

2002 Pontiac GTP, red (58,000 miles) strictly driven to car shows, currently in storage

2003 Pontiac GTP, LE, blue/black (187,000 miles) all stock, daily driver


#23 wstefan20

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Posted 10 December 2017 - 05:16 AM

Ok. Got a bit confused in the initial description. Sounds like a circuit is failing when warmed up. Definitely could be the fuel pump. I hate to say it, but the best way to troubleshoot something like this with no codes is to get a good scan-tool with data logging ability. I'd recommend the launch easydiag 2.0 plus that I've used for over a year and I love it, but unfortunately the price jumped up from $70 to $150 and you can't buy it on amazon anymore. I'm sure others will jump in to name their favorite tool.

 

I wouldn't go re-wiring the map sensor unless you've confirmed that the circuit is a fault. A cheap mulitmeter will confirm this.


  • NotEnoughGPs likes this

#24 wstefan20

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Posted 10 December 2017 - 05:17 AM

From extensive reading on the CPS, I believe that it is not to blame for the no-start condition. The CPS does not get heatsoaked according to everything I have read. When a CPS is faulty, it can cause the engine to stop at any time. Also, I was asked to observe the RPM's on the tach when cranking. If the CPS is bad, then the tach will be sitting at zero . That is my understanding. 

As for a scan tool diagnosis, that is going to occur soon.

I agree with your conclusion on the CPS, though I've seen some weird stuff, I don't think this is to blame here.


  • NotEnoughGPs likes this

#25 NotEnoughGPs

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Posted 13 December 2017 - 04:51 PM

UPDATE: I am still trying in my spare time to work on this GTP. 

In the past week, I have had no trouble getting it started on a cold engine. Now, that has changed again, I tried to start it to move it into the garage and it would not start after 8 attempts. It cranked, but would not start, a few times it almost started. A few hours later, I tried starting it again and it started right up.

 

I had stopped at a shop few days ago about 5 miles away and talked with a mechanic who is recommended by some other local people I know. I explained to him what has been happening with the GTP. I told him I wanted to install the exhaust with the low mileage catalytic converter, and replace the rear valve cover gasket, and some other items. 

I told him that I may be able to find what is causing the car to not start, and he said if I can't to call and make appointment and leave the car. He said he would check the fuel pressure gauge, and hook up a scan tool to check for codes, and he would check wires with a ohmmeter, he has done that before.

 

Anyways, last night, when I googled "3800 engine cranks but no start", one owner said he had a problem with the ICM (Ignition Control Module). He removed it and the underside was severely corroded. I had never had the coils or ICM removed from this car (actually never removed it from any GP I have owned) 

When I did take off the ICM, it was severely corroded, both the module and the back plate. I removed the corrosion by had with various grades of sandpaper until the surface was shiny.

 

After putting on a coat of dielectric grease, and carefully putting everything back together, I turned the key to start and without hesitation, the engine started up.

 

I did not replace the ICM, I have other ones in the garage, but now I am not going to replace the one in the car.

I want to take it for a long drive and see if the boost gauge shows the level of boost as it was before.

 

I will report back again soon. 


Pontiac owner since 1999, driven over 500,000 actual miles in Grand Prix's I have owned

2001 Pontiac GTP, silver (31,000 miles) too many mods to list, currently in storage

2001 Pontiac GTP, silver (98,000 miles) small turbo, built tranny, currently in storage

2002 Pontiac GT, 40th Anniv, dark cherry (273,000 miles) mild mods, daily driver

2002 Pontiac GTP, red (58,000 miles) strictly driven to car shows, currently in storage

2003 Pontiac GTP, LE, blue/black (187,000 miles) all stock, daily driver


#26 wstefan20

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Posted 13 December 2017 - 05:31 PM

UPDATE: I am still trying in my spare time to work on this GTP. 

In the past week, I have had no trouble getting it started on a cold engine. Now, that has changed again, I tried to start it to move it into the garage and it would not start after 8 attempts. It cranked, but would not start, a few times it almost started. A few hours later, I tried starting it again and it started right up.

 

I had stopped at a shop few days ago about 5 miles away and talked with a mechanic who is recommended by some other local people I know. I explained to him what has been happening with the GTP. I told him I wanted to install the exhaust with the low mileage catalytic converter, and replace the rear valve cover gasket, and some other items. 

I told him that I may be able to find what is causing the car to not start, and he said if I can't to call and make appointment and leave the car. He said he would check the fuel pressure gauge, and hook up a scan tool to check for codes, and he would check wires with a ohmmeter, he has done that before.

 

Anyways, last night, when I googled "3800 engine cranks but no start", one owner said he had a problem with the ICM (Ignition Control Module). He removed it and the underside was severely corroded. I had never had the coils or ICM removed from this car (actually never removed it from any GP I have owned) 

When I did take off the ICM, it was severely corroded, both the module and the back plate. I removed the corrosion by had with various grades of sandpaper until the surface was shiny.

 

After putting on a coat of dielectric grease, and carefully putting everything back together, I turned the key to start and without hesitation, the engine started up.

 

I did not replace the ICM, I have other ones in the garage, but now I am not going to replace the one in the car.

I want to take it for a long drive and see if the boost gauge shows the level of boost as it was before.

 

I will report back again soon. 

Well that's just another case where corrosion is a pain in my rear! I should have thought of that though. Some other strange electrical stuff was going on with another member awhile back and it ended up being corroded PCM connector.

 

And personally, I just had a fight with the ABS module and it being corroded. Course, that was so bad, I ended up having to replace some of the terminal pins! (not very fun)

 

Hopefully that was it, and it runs like a champ now!






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