Turbo Grand Prix Starting Issues

[Addicted To Boost]

I've been trying to figure this one out for a while, and I'm stumped.

1989 Turbo Grand Prix- runs great, but starts very hard.  If I try to crank it over, it will fire once, then never again.  So after trying this probably 10-20 times (key on, crank, doesn't catch, key off, repeat), it will eventually start and be fine.  Typically for the rest of the day, it will start fine.  Then, once it sits again, it doesn't want to start.  I have tried starting it in clear flood mode (accelerator pedal to the floor), and also holding the accelerator 1/4 of the way down, but neither condition helps.

The following have been replaced with new parts: fuel pump and sending unit, fuel filter, fuel pressure regulator, Ford yellow top injectors that measure 14.5 ohms, used and working ICM and coils from an 04 Impala, spark plugs and wires, O2 sensor, crank sensor, alternator, and battery.

Side note- I also recently acquired a 1990 Turbo Grand Prix that didn't run, due to faulty original injectors.  I replaced those with the Ford yellow top injectors, and it behaves the same way.  Super hard starting, but now runs fantastic, otherwise.

Anyone have any insight?

[pwmin]

Is the starter engaging?  Have you tested the MAP sensor? 

[Addicted To Boost]

They both crank over fine and run great, once started.  It isn't throwing any codes for the MAP and the reading seemed reasonable when I had it plugged into the Tech I.  Maybe I wasn't clear in my original post, but they crank over perfectly fine.  They just act like they aren't getting fuel when you crank it over.

[pwmin]

I just went through bad MAP sensors when I supercharged the GT and didn't get codes.  It would crank fine, but not start most of the time.   Just a thought as I had never had that issue before, but it sounds like you checked that out.  I was just thinking about another issue we had with a starter not engaging (it would spin every time you cranked, but it would only engage 1 out of 10 times; I didn't read correctly.

Crank sensor?

[Addicted To Boost]

Crank sensor has been replaced.

[55trucker]

Do you have access to a noid light?, altho you've replaced much of the mechanical parts related to the fuel system you still do not know when cranking if the injectors are getting a proper pulse to them to actually open the injectors.

If you were to *test* each of the plugs for spark (spark tester) as the engine is cranking is there a constant spark on all 6?

Have you done a compression test on the engine?

Take 3 items to get the engine to fire .....compression, fuel, ignition,

being a turbo engine there's no boost when the engine is just cranking

[pwmin]

2 hours ago, Addicted To Boost said:

Crank sensor has been replaced.

Good lord, I can't read!  lol

[Addicted To Boost]

1 hour ago, 55trucker said:

Do you have access to a noid light?, altho you've replaced much of the mechanical parts related to the fuel system you still do not know when cranking if the injectors are getting a proper pulse to them to actually open the injectors.

If you were to *test* each of the plugs for spark (spark tester) as the engine is cranking is there a constant spark on all 6?

Have you done a compression test on the engine?

Take 3 items to get the engine to fire .....compression, fuel, ignition,

being a turbo engine there's no boost when the engine is just cranking

I don't, but that's a good idea.  It's strange that both cars are behaving identically, though.

Yes, I did a compression test when I replaced the plugs 4 years ago, good on all cylinders.

[Pontiac6KSTEAWD]

I have a couple suggestions. My TGP did this back in the day, and it was a bad vacuum leak. I cant remember the entire process that I went thru, but I remember that it was where I expected it -not- to be. I do remember pulling the EGR off the throttle body, and blocking the port, and also pulling the intake plenum, and plugging the PCV valve at the plenum, and the 3 way port at the back of the throttle body. Basically, everything that would create excessive vacuum, I blocked the ports for. And it fired up beautifully. Than it was just a matter of going back, one by one, and plugging those vacuum lines in, until the starting problem returned.

One of the key things is once it starts, dont let it run long, you dont want to create any heat in the engine, to allow the test allowed to be repeated in one sitting.

This was like 10 years ago, but I seem to remember it was a combination of both the PCV line, and EGR valve. But I have owned quite a few 2.8/3.1 engines, so its all a blur at this point.

[55trucker]

I can see vacuum leaks being an issue as well, where all of the molded vacuum tubing is concerned are the original rubber nipples still on the ends?

[Addicted To Boost]

On 3/12/2021 at 3:37 PM, pontiac6ksteawd said:

I have a couple suggestions. My TGP did this back in the day, and it was a bad vacuum leak. I cant remember the entire process that I went thru, but I remember that it was where I expected it -not- to be. I do remember pulling the EGR off the throttle body, and blocking the port, and also pulling the intake plenum, and plugging the PCV valve at the plenum, and the 3 way port at the back of the throttle body. Basically, everything that would create excessive vacuum, I blocked the ports for. And it fired up beautifully. Than it was just a matter of going back, one by one, and plugging those vacuum lines in, until the starting problem returned.

One of the key things is once it starts, dont let it run long, you dont want to create any heat in the engine, to allow the test allowed to be repeated in one sitting.

This was like 10 years ago, but I seem to remember it was a combination of both the PCV line, and EGR valve. But I have owned quite a few 2.8/3.1 engines, so its all a blur at this point.

Did you find your EGR to be sticking open, then? That would actually make a lot of sense.  Both cars have new PCV valves and as far as I can tell, no vacuum leaks.  All original plastic vacuum lines and rubber couplers.  All vacuum- controlled accessories work properly, so I don't think the vacuum system has leaks.  Typically when something goes awry there, the cruise control won't work or the vents will be stuck on defrost- both of which work properly.

Is there a good way of testing EGR function? Mainly to ensure it is fully closing when it should be? Only the 88-89 2.8 and 89-90 turbo engines received the vacuum-controlled EGR. The 90+ cars had the "digital" ones.

[55trucker]

1 hour ago, Addicted To Boost said:

Is there a good way of testing EGR function? Mainly to ensure it is fully closing when it should be? Only the 88-89 2.8 and 89-90 turbo engines received the vacuum-controlled EGR. The 90+ cars had the "digital" ones.

One uses a handheld vacuum pump to test the vacuum side of the EGR, when attempting to pull vacuum either the EGR will or it won't, if it will not then the diaphragm has failed & that would be the source of the vacuum leak. The pintles are spring loaded. Remove the EGR and have a look at the pintle, you should be able to freely move it by hand. Most of the original Rochester EGR's when turned upside down one can see the diaphragm plate back behind the ribs of the housing.

Edited March 15, 2021 by 55trucker

[Addicted To Boost]

Right, but is there a way of testing to see if the EGR is sticking open while running? I don't think I have a vacuum leak going on, but if the EGR is stuck open all the time and pumping exhaust gases into the intake manifold and causing a low vacuum situation, that would certainly explain the hard starting.

Edited March 15, 2021 by Addicted To Boost

[55trucker]

With or without the engine running you *should* be able to get your finger in between the housing ribs on the bottomside and push up on the diaphragm plate. Doing so moves the pintle shaft, you should be able to feel & hear the shaft moving. Try this.....

[mfewtrail]

A vacuum leak large enough to cause starting problems would make the idle absolutely skyrocket when the engine actually does run..  Test for proper fuel and spark after it's sat. Don't assume anything "new" or replaced is good, test to be sure.

 

Out of curiosity: When the fuel pump was replaced did you reuse the pulsator or splice in a new piece of submersible rated fuel hose?

 

[Addicted To Boost]

2 hours ago, mfewtrail said:

A vacuum leak large enough to cause starting problems would make the idle absolutely skyrocket when the engine actually does run..  Test for proper fuel and spark after it's sat. Don't assume anything "new" or replaced is good, test to be sure.

 

Out of curiosity: When the fuel pump was replaced did you reuse the pulsator or splice in a new piece of submersible rated fuel hose?

 

I used a Bosch fuel pump, as the AC Delco pumps don't seem to be good quality anymore (installed one first and that had lackluster pressure).  I replaced the pulsator with the piece of hose that came with the new pump. I seem to remember it being 38 PSI.

Edited March 16, 2021 by Addicted To Boost

[pwmin]

Does your EGR have 5 pins?  I think they used the same one for a long time.  Here's a way to check voltage.  This seems to explain everything pretty well.  If the voltage in C(?) is incorrect, it could show it being stuck open of closed.

[Addicted To Boost]

19 hours ago, pwmin said:

Does your EGR have 5 pins?  I think they used the same one for a long time.  Here's a way to check voltage.  This seems to explain everything pretty well.  If the voltage in C(?) is incorrect, it could show it being stuck open of closed.

Did you mean to attach something? Yes, they are 5-pin connections.

Edited March 17, 2021 by Addicted To Boost

[pwmin]

10 hours ago, Addicted To Boost said:

Did you mean to attach something? Yes, they are 5-pin connections. Just for fun, I unplugged the 5-pin EGR connector on both cars and they both fired right up.

Haha, yes I did.   Oops.  Guess there, you go. 

 

https://easyautodiagnostics.com/gm/4.3L-5.0L-5.7L/egr-valve-tests-1