Hard to start warm, but not cold or hot

Hard to start warm, but not cold or hot

Postby RussTypeS [OP] » January 6th 2009, 5:54pm

So the van starts fine cold (sitting overnight), and it starts fine hot (like after filling up with fuel), but if I let it sit for say 1-6 hours it's hard to start. When I try to start it usually it will catch right away then stumble out. When I try to start it again it will turn over for maybe 10 seconds before it catches and then runs fine. I've found that if I give it a tiny bit of throttle when I suspect it will be hard to start it will catch the first time, run rough for a second, then idle normal. I should also mention that "normal" is a little rough and has been for a while (at least 50k miles). Not rough enough to bother me, and it was still rough after I changed plugs, wires, cap, & rotor (which have not been done recently, but I don't suspect that is the problem).

I searched around a bit but I can't find anyone with this same problem. I have a few ideas but I'm not really familiar with CPI so I may be way off, what do you guys think?
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Re: Hard to start warm, but not cold or hot

Postby Leeann_93 » January 6th 2009, 8:17pm

What year is your van? You say CPI, so 92-95?

Have you ever looked at/cleaned your EGR valve? How about your IAC?
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Re: Hard to start warm, but not cold or hot

Postby RussTypeS [OP] » January 6th 2009, 8:21pm

Sorry, should have included that info in the original post. It's a 95 with 212k on the clock. I haven't checked either of those but it sounds like I should give them a look. Thanks!
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Re: Hard to start warm, but not cold or hot

Postby astro355 » January 6th 2009, 9:11pm

Check/clean the back of the throttle plate on the throttle body.
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Re: Hard to start warm, but not cold or hot

Postby RussTypeS [OP] » January 23rd 2009, 7:21pm

Took the EGR off, no problems but I cleaned it out anyway. The IAC was pretty gunked up so I cleaned it out as well, also cleaned the back of the throttle plate and the IAT while I was in there. None of this seemed to make any difference, any other ideas?
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Re: Hard to start warm, but not cold or hot

Postby astro355 » January 23rd 2009, 8:07pm

When was the last time the air filter was changed/checked?

Did you check fuel pressure?

What is the condition of the electrical system? Battery, alternator, wires, corrosion on terminals?
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Re: Hard to start warm, but not cold or hot

Postby RussTypeS [OP] » January 23rd 2009, 8:15pm

Checked the air filter last night when I had it off to clean the IAC and EGR, looked fine. No corrosion on the battery, but it's not like it has trouble turning over it just wont catch. Everything electrical is in good shape.

I haven't checked the fuel pressure, but I suppose that's next on my list. I don't have a fuel pressure gauge that can handle efi pressures, what should I look for at the parts store? How does the gauge connect?
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Re: Hard to start warm, but not cold or hot

Postby astro355 » January 23rd 2009, 8:21pm

The gauge connects to the schader valve. Its universal for GMs.

And actually, you would have to check for corrosion IN the terminals for the battery and the starter. Any corrosion there will produce a volt drop that maybe enough to not let your van start. Corrosion creates resistance in an electric circuit, as does heat. The more heat you have in an electrical circuit, the more voltage required to operate said circuit. So, whey you think about all of the different circuits that require voltage during startup, you could very easily not have enough voltage to fire one circuit, say the injectors.

Yeah, cause even if you have adequate fuel pressure, the injectors may not be firing. Maybe before you get that fuel pressure gauge, trying shooting some propane down the intake when you have this no start condition. Have another person turn it over while you operate the propane, if it fires, then you would know that you weren't getting fuel in the cylinders.
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Re: Hard to start warm, but not cold or hot

Postby Leeann_93 » January 23rd 2009, 8:25pm

You need a fuel injection pressure test kit - it'll need to do at least 65 psi. It connects to a schrader valve on the fuel pressure line as it goes into the intake manifold.

Most parts places have them for about $30 and Harbor Freight has a kit for about $12.


EDIT: damn, beaten by 355 again (whose post wasn't there when I started typing, I swear)
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Re: Hard to start warm, but not cold or hot

Postby astro355 » January 23rd 2009, 8:29pm

Leeann_93 wrote:You need a fuel injection pressure test kit - it'll need to do at least 65 psi. It connects to a schrader valve on the fuel pressure line as it goes into the intake manifold.

Most parts places have them for about $30 and Harbor Freight has a kit for about $12.


EDIT: damn, beaten by 355 again (whose post wasn't there when I started typing, I swear)


Don't worry, dear. Its those super moderator powers! :screaming:
Diagnose 1st, never be a parts changer!

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Re: Hard to start warm, but not cold or hot

Postby Leeann_93 » January 23rd 2009, 8:31pm

astro355 wrote:Don't worry, dear. Its those super moderator powers! :screaming:



:lol:
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Re: Hard to start warm, but not cold or hot

Postby RussTypeS [OP] » February 6th 2009, 6:53pm

It turned out to be a leaking fuel pressure regulator. Diagnosed by good fuel pressure at first but it dropped steadily as soon as the pump stopped running (about 2 seconds after turning the ignition to "on" but not starting), clamping the fuel line from the tank did not stop the leak so it had to be something in the CPI unit. It turns out that when the FPR leaks it spills fuel in half of the intake plenum (so only one side of the engine is rich) causing the rough idle and hard starting unless the throttle is open (makes sense, you have to lean it out a bit to compensate for all the fuel pooled in the LIM).

Once I removed the UIM I found almost exactly what this guy found: http://www.treasureboards.com/blazer/cpi/CPI.html. $45 and a trip to Autozone later I have a new FPR and a smooth running van. Thanks for the help guys.
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Re: Hard to start warm, but not cold or hot

Postby astro355 » February 6th 2009, 9:53pm

Great! Glad to hear you got it running good again.
Diagnose 1st, never be a parts changer!

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