I'm at a complete loss on this; I apologize in advance for a lengthy post, but I'd sure appreciate any insight or suggestions. Here's the scoop:

The car is an '89 IROC-Z and currently has approximately 800 miles on the new engine ...details follow.

-new 350 H.O. (car is a stock L98)
-stock ECM and PROM
-every engine sensor is new
-SDPC TPI baseplate
-24# SVO injectors
-NGK TR-55 plugs gapped at .045"
-Taylor Spiro Pro 8mm wires
-stock exhaust manifolds
-new D.U.I. distributor
-new D.U.I. Screamin' Demon coil
-2.73 stock rear
-new 700R4 transmission

I finished the install and fired it up on Nov. 3; the car ran fine for a month and then started acting like it was cutting out or missing at highway speeds. This was intermittent, but gradually became constant and is now to the point where any acceleration other than slow and gradual results in the flame being "blown out" (that's what I was told) - the car falls on its face, stumbles, and feels like it has no power at all.

The first set of plugs was gapped at .060", and I did that because the coil instructions said that it was OK to gap them that wide due to the high output of the coil - the car ran fine for a month with that gap. The plug electrodes were an off-white, not blistered, and there was no evidence of detonation.

The second set of plugs was gapped at .050" because the off-white color of the first set made me think that I was running lean, but the more narrow gap didn't make much difference; I no longer had the lack of power or stumbling, but the car felt like a V6 instead of a 350. I then regapped those plugs to .055" and the car was falling on its face again and running pig rich, so I bought a set of new plugs and gapped them to .045" - the car now runs worse than with a .055" gap and is still running pig rich. This problem occurs under no-load conditions as well as under load.

Here's what I've observed:

- Vacuum as tested at the plenum port where the (stock) FPR connects is approximately 12"-13". It went as high as 18" when I opened the throttle.

- Fuel pressure under load, no load, and with the engine off is approximately 43 lbs. - the fuel pump is 7 months old and is a stock replacement. The fuel filter is new.

- Timing is at 10 degrees BTDC as per the booklet that came with the engine.

- Spark plugs 6 and 8 looked brand-new when I pulled them; it was as if they had never been fired. I can feel #6 and #8 injectors pulsing, so that may explain the rich-smelling exhaust if those two cylinders aren't firing.

- I have no trouble codes at all. I'm fairly certain that the ECM is functioning because I get a distributor reference pulse (12) and I got a MAF code when I unplugged it.

- PROM tuning or a custom PROM is severely lacking.

I have not tested any sensor voltages because, frankly, I don't know how.

I'm probably going to ask some dumb questions if I get any replies to this post, but bear with me - I'm approximately $7000 into this car and I just can't afford to have somebody look at it. Thanks in advance for whatever you can offer. I'm tired and frustrated, so let me know if I forgot to add some info.

- 89_IROC

 

i'd look for a vacuum leak and i'd make sure all the valves were opening and there wasn't any problems in the valve train or with the cam.

 

Fuel pressure should be some lower value, like 38 psi or so, with the engine running and the line connected normally; it should increase to 44 psi or so if you disconnect the line. This is assuming the stock FPR.

Try your OE injectors and see if it's any different. You're definitely getting too much fuel (at least at WOT) if you're using the stock chip with 24# injectors, although at moderate throttle opening, the ECM should be able to adjust the pulse width adequately.

Check your plug wire routing, and which wire goes to which cyl, carefully. Then check it again. Then get somebody else to check it.

You should have considerably more vacuum than that. If it has the stock 350 HO cam in it, your idle vacuum should be around 18-20" at 750 RPM in neutral and around 13-14" at 650 RPM in gear.

 

Thanks for the quick replies, ede and RB.

ede - should I check the valves, valve train, and cam since this is a crate
motor? I didn't build it.

RB83L69 - Unfortunately, I don't have the OE injectors anymore, nor do I know of
anyone to borrow a set from - you're certainly correct about getting too much fuel though. Are you certain about that fuel pressure?

Are there any other places where you recommend that I check vacuum?

That's a good point about plug wire routing, and it's easy to check. Thanks to
you both for the quick responses.

- 89_IROC

 

TTT...

Anyone else have any ideas at all? A friend of mine suggested checking out the coil and ignition module, which made sense to me at the time. #6 and #8 plugs were not firing (this is an assumption based on appearance - those plugs looked brand-new as opposed to the other 6, which have whitish electrodes); this has happened with two sets of plugs and two sets of plug wires...it seems that the odds against two bad wires in two consecutive new sets as well as two bad plugs in two consecutive new sets would be uncountably high.

The first set of plugs, pulled just after the car started having issues, all had whitish electrodes, which indicated to me that they were all firing.

I'm not a wrench by any stretch of the imagination and I don't know why the ignition didn't occur to me as suspect, but what my friend said made sense - at least on the surface. Can anyone substantiate or refute my information?

- 89_IROC

 

have you tried replacing the distributor cap and rotor? if 6 of the 8 are firing and you've tried multiple plugs and wires, cap is about the only place left to look. Can you verify the plugs are running or not with a tester? Could be those are the only two running properly...

 

You know, I actually did replace the distributor cap with my previous cap because one of the brass fittings came out of the new cap, and the cap from my stock distributor (an Accel unit) wasn't giving me any problems while it was in the previous engine.

#6 and #8 plugs still weren't firing after the swap. I haven't tried replacing the rotor because, frankly, it never occurred to me since everything from the pan up is brand-new equipment with ~800 miles on it. Granted, that doesn't really mean anything, but one generally expects brand-new items to work. That's a good item to check though; if the distributor cap is bad on a brand-new distributor, one should probably start suspecting other items as well. Thanks for mentioning that.

I don't have access to a tester, but I'll bet I can find someone to test them. #6 and #8 look brand-new...literally as if I'd pulled them straight from the box. Take a brand-new plug and compare it to one that's been firing in an engine - that's the difference between #s 6, 8, and the other six plugs. I still find it difficult to believe that two plugs each from two consecutive new sets are bad and that I happened to get both bad plugs in the same cylinders each time, you know? I'm not knocking your suggestion by any means - I'm just saying that it would be kinda freaky if you're right

Please keep ideas coming my way - I'm going to test the coil and ignition module in addition to the rotor and see if I can find a culprit...or 3

- 89_IROC

 

Is it possible that during the "first month the car ran good" that it got over-revved?? Possibly bending some pushrods or breaking some rockers?? I would pull the valve covers and take a look, it won't cost anything since you can reuse the valve cover gaskets. Also possible the cam lobes went flat?? I see that motor uses a flat tappet cam. Check to see if the valves on the dead cylinders are working. If you have access to a compression gauge do a compression check.
Just some things to check, hope you figure it out!

Dave

 

Dave,

edit: actually Dave, it's a roller cam motor, and the guys at Chevy mentioned both flattened cam lobes AND blown head gasket. Thanks for the post!

The engine wasn't over-revved that I recall; I'm approximately 7 grand into the engine and poor to boot, so I was trying to keep an eye on the RPMs until I hit at least a couple thousand miles

To address your comments, I eliminated the ignition system - known-working coil and cap have been tried with no change in symptoms, my ignition control module tested good at several different parts stores (doesn't necessarily mean anything, I know), and my rotor is fine, although I don't think that would play a part anyway.

#6 and #8 cylinders are not firing - the spark plugs look like they just came out of the box and I've used two different sets of new plug wires.

I checked the oil today and it seems a bit "watery" (for lack of better terms). I didn't particularly notice a milky appearance or oil/water separation on the dipstick, but the oil level was approx. 1/2" above the "full" indicator and I'm absolutely positive that I didn't overfill it. The car blows water droplets out of the exhaust even when warm and it's running really rich (I can smell it in the exhaust). All injectors are working. No plugs are fouled.

I have not monitored my coolant level closely, although it always seems to be full when I open the cap. Oddly, I could never seem to keep the minimum coolant in the overflow reservoir...that just occurred to me.

Here's the conclusion that I came to with the help of NAPA and the guys at my local Chevy dealer: I'm looking at a possible blown head gasket. It makes sense when I think about it...

1. fuel going into #6 and #8, but not being burned because compression is so low or absent.

2. spark plugs in those two cylinders look brand-new when I pulled them (two consecutive sets of new plugs) and it's the same two cylinders every time. It's the same regardless of plug gap.

3. oil dipstick reading over-full, oil has a "watery" consistency.


This is by no means conclusive proof, and my next step is a compression test on all 8. It'll be a few days before I have enough cash for a tester, so I'll update once I get some results.

This is a major pisser; if it is a head gasket, I'm awfully glad that I have some of this crate motor warranty left

- 89_IROC

 

I hate to break it too you tiger, but its NOT a roller cam motor unless YOU put a roller cam in it. and that would have required machining the heads, and would void your warranty, so I'm pretty sure its a hydralic flat tappet cam.

And if the engine wasn't broken in properly, there could possibly be flattened cam lobes.

your #6 and #8 cylinders ARE FIRING. because i don't think your engine would be pulling 12-13" of vacuum with not ONE but TWO dead cylinders.

why the plugs are so clean, i don't know, but those plugs are firing.

The head gasket shouldn't have blown on a brand new motor. Although it is possible.

whats your oil pressure like at idle?

 

Originally posted by scottland
I hate to break it too you tiger, but its NOT a roller cam motor unless YOU put a roller cam in it. and that would have required machining the heads, and would void your warranty, so I'm pretty sure its a hydralic flat tappet cam.

Dammit...I was misinformed, then. I learn something new every day about these things.


And if the engine wasn't broken in properly, there could possibly be flattened cam lobes.

No one mentioned anything to me about a "proper" break-in procedure because I specifically asked when I bought the engine, and there wasn't anything mentioned in the booklet that came with the engine.


why the plugs are so clean, i don't know, but those plugs are firing.

I should've clarified this - I realize that the plugs themselves are firing, ie they're sparking, but I don't see how combustion could be taking place in those two cylinders with the plugs looking like they do. They literally look as if I pulled them right out of the box brand-new. Maybe a picture would help illustrate this. Of course, I won't know anything for sure until I do a compression test.


The head gasket shouldn't have blown on a brand new motor. Although it is possible.

I agree completely. Since you mention flattened cam lobes, how does this happen and how soon can it happen with a crate motor?


whats your oil pressure like at idle?

It's in the range of 40-45 psi at idle, closer to 60 under load, but it's been like that since day one.

- 89_IROC

 

Next time you fire it up, go get some water. After the motor has gotten to operating temp, dribble some water on the headers. It should burn off so fast that it just seems to roll of the header, leaving the header looking un touched. If cylinders 6 and 8 arent firing they water will not act the same on the header because of the reduced heat.

Have you smelled your oil? gas smell? antifreeze? if you smell nothing you could take a dab and touch it to your tounge, sweet is antifreeze. Your getting something in your oil, you just need to figure out what that is.....

To check for worn cam lobes, disconnect your ignition coil, take off your vavle covers. Have someone turn over the engine and watch rockers. Worn ones are verry noticable, they barely move. Take time to watch every rocker.

Edit: Proper break in is critical for flat tappet cams and seating the piston rings. I always use light valve springs(so I dont wear the cam down during break in). Then you fire the engine and let it run at apporx 2000rpm for 15-20 minutes. Then change the oil. Then 500 miles of easy driving.

 

Would this also apply to stock exhaust manifolds, which is what I'm runnning? Would dribbling water onto the manifold at #6 and #8 exhaust ports do the same thing? Thanks for that tip - I hadn't thought of that.

- 89_IROC

 

with a roller camshaft, there really isn't any break in period needed.

its a good idea too take it easy on it, for the first few miles, but nothing special.

BUT with a hydralic cam, like you have in the 350HO, you have to run the engine at 2000-2500rpm for the first 20-30mins.

this ensures that oil makes its way to the camshaft.

if you didn't break the cam in, there is a good chance, that you have a flat lobe or two.

your oil pressure is fine, I doubt you have a blown head gasket.

sounds like major tuning issues, and major ignition issues.

 

OK. It's been awhile, and I have new info on this. I was initially running with the stock PROM (mainly because the car initially ran without any problems, and I couldn't afford a custom PROM at the time), but I have since installed a custom PROM from www.pcmforless.com (Craig Moates recommended them).

It was installed a couple of months ago, and the car runs far better than it previously did; it rarely falls on its face like it used to and I can actually accelerate without the engine bogging down. My gas mileage blows, but (I think) that's because my cooling fan is coming on at 178 degrees and cutting off at 171. I had the chip burned with a turn-on time of 200, but according to my local dealer it's coming on at 178. I'm not getting to closed loop very often, if at all, with a 180 thermostat and I can still smell fuel in the exhaust.

Hopefully it's just a matter of tuning at this point. Thanks for all the responses so far.

- 89_IROC

 

I would fire the car up at night with the hood popped and check to see how many of your plug wires are arcing.

 

Anything is possible I suppose, but arcing wires seems fairly remote at this point; they're practically-new Taylor 8mm Spiro Pros with less than 2000 miles on them. I'm leaning more towards PCM tuning at the moment, but it sure wouldn't hurt anything to check for arcing wires - I'll admit that it hadn't occured to me. Thanks for the suggestion.

- 89_IROC