Hi, I've followed this site for some time but this is the first problem I've not been able to solve by search.

I have a 95 LT1 that ran perfectly last week before I replaced the leaking intake manifold gasket. While replacing the gasket I also replaced the egr valve (gm unit), thermostat (aftermarket and factory temp), and oil and filter. I drained the coolant and was extra careful not to get anything on the opti.

Now I have two new issues. First is now takes about 5 slow seconds of cranking to start if its been sitting for more than a few hours, it used to start instantly. Once it starts it runs great for about 15 minutes. It has lots of power and idles well. Then all of the sudden it will start getting sluggish and choking like it's starving for fuel. I'll eventually get a check engine light but I haven't been able to check it because it doesn't stay on when the car is restarted. Btw, I can restart it even when it's hot and it will start up right away and run great again for a while. Also, when I start it now I now hear the smog pump running loudly. I don't recall hearing this before but I suppose I could have not been paying attention.

I replaced the fuel pump last night as I thought that could be it along with the relay. I've checked to see if the injectors and the regulator are leaking and they both check out good. If there was a vacuum leak I would think the problem would be noticeable all the time. The injectors, o2 sensors, plugs, air filter, and coolant temp sensor are all less than a year old. I'm still having this problem and I'm beating my head against the wall because I'm afraid to drive it now. What should I try or check next?

 

I remembered another possible clue. Yesterday when running some tests it was shifting at over 6k rpm at wot. That concerned me greatly.

 

Ok I went and gathered the OBD codes. It's giving a C12 on 1, a H64 on 4, and a H65 on 9.

 

Could it be timing related?

 

I don't see how, I didn't mess with the timing. I'm beginning to think it may be the head gaskets. I noticed white smoke on startup and it would explain why its hard to start (if coolant is leaking into the cylinder when it sits). Also last night I heard water boiling in the system too. I don't know how it happened if this is the case, it never over heated according to the gauge. It got to the upper range once when it needed bleeding but I never let it hit the red. This car is going to give me a breakdown.

 

Sorry, I thought that you had to pull distributor to get the intake manifold off. Maybe it's different on the LT1's

Good Luck. I hope it's not head gaskets.

 

Yeah the LT1s have the optispark distributer on the front of the engine. Probably the only good thing about them is that you don't have to take it off to do top end work. lol

 

If the check engine light came on, a code should be stored.

What you describe is symptomatic of an EGR valve stuck open. Wonder if they gave you the right one? There are two types and they look the same externally. I'd put the old one back on and see what it does.

Btw...why drain the coolant for this? The LT1 intake is dry. Other than a minor amount you lose disconnecting the tb, there's no need to drain it.

 

I posted the codes in one of my other comments. I'll put the old egr back on and see what happens. Thanks for the idea. Do you think that could be causing the boiling as well? I drained the coolant cause I didn't realize it was a dry system, doh. I'm wondering if perhaps it had sealant pellets in it and when I drained it I drained them causing this issue to become visable. I'm debating buying some and seeing what happens.

 

Even though your O2 sensor is relatively new the car is going into "closed loop mode" in around the time period you're talking. The o2 could still be at fault. Its once its "warmed up" right?

 

I was thinking about that. When I'm driving it there is a place where I usually see my car reach normal operating temp. The chugging almost stalling starts about 5 times that distance or time.

 

C12 means nothing; ECM is working -you get that code every time

H64 on 4 is a PCM code for left O2 sensor lean
H65 on 9 is for the throttle adjuster assemble on the ASR system.

They are both "H"istory codes so not sure if either is relevant to your issue at hand.

 

How about another guess? Maybe when you refilled the coolant there was still some air left in the system and you hear it gurgling. Also, if this is so, maybe the cts is not reading correctly and the car remains in "open loop" mode. In this mode, the ecm ignores the O2 sensors. It does seem like there is a problem related to the changeover to closed loop and I agree that it is possible that an O2 sensor is at fault.

If you didn't have head gasket issues before this work, it would be quite coincidental to have them now.

Did you bleed the cooling system when you filled it?

 

I think I verified that it is the head gaskets. I had someone start the car while I stood behind it. Got some white smoke that smelled sweet like antifreeze. I had also tried putting the old egr valve back on and replacing the radiator cap.

I did bleed the system and no head work had been done to it previously that I'm aware of. I'm guessing just the change of pressure from debolting the intake finished off an already weak gasket.

Now I'm thinking maybe a new long block from golen, just have to save and find a reputable shop to do the swap. I don't trust myself to do it I don't think.

 

You might be able to prove your diagnosis with a compression test.

 

Pull off the rad cap (when cold obviously) start it up. See if you see bubbles leaking to the surface. Easy diagnosis for a leaky headgasket.

 

Ok, troubleshooting update: I borrowed a block tester from Autozone. It suggested testing for 2 minutes I went ahead and did about 5 minutes and the liquid never turned yellow. Supposedly this means the combustion chambers are sealed to the coolant. Though I don't know how accurate of a test this is.

My next hypothesis I'm working on is perhaps clogged catalytic converters. When I bought the car one of the injectors was stuck open and pouring fuel into the system causing it to run rich. After replacing the injectors it ran good but maybe one just finished getting plugged up. My console does get warm when driving and I read in another thread this might be a sign of clogged cats. What do you guys think?

Oh also one interesting piece of info I haven't figured out. If I run the car to where it's running crappy and let it sit for a few hours to 1 day then when I go to start it, it starts very reluctantly. However, if I let it sit a few days then sometimes it starts right up with no problems at all it seems.

 

I believe a quick test for clogged cats is to check whether the exhaust pipes upstream and downstream feel roughly the same temp. (carefully, of course) The pipe upstream of a clogged cat will be much hotter.

 

Look for the simple connection. My C5 was doing some really strange things one time. Would only stay started for about 3 seconds, chug then die. I posted the codes to the forum. From the replies if there was one possible cause there were a 100. Try this, try that. There were a lot of suggestions to check for a broken valve spring. We checked the valve springs and they were fine.

It was a loose connection on the air intake. Accidentally bumped something and the entire air intake fell apart. Put it back together 'tight' and it ran like a champ. Go over all your connections. Make sure they're tight and correct. It's probably something simple.

 

What Mundo just said.

As for the clogged cat...maybe. Fastest way to "test" that is when the symptom is occuring, heavy throttle (WOT) will result in:
Low power
TONS of intake/induction noise. Tons. Ridiculous intake sound.

Light throttle would result in normal operation.

What about fuel filter/pump/pressure? Have you tested fuel pressure when the symptom is occuring?

When it's hard to start, does using WOT during cranking expedite the starting process?