HELP

Where do I start.

My wife's C4 came home on the tow truck a couple of weeks ago. The ECM does not display any codes and my scanner shows all systems normal.

Fuel pressure and regulator are good. 36 lbs regulateted and 43 unregulated

ECM is new.

EGR is new. EGR solenoid holds vacuum.

TPS is good.

Air purge solenoid is BAD and vacuum is blocked off.

IAC is good.

Got plenty of spark. the HEI tests good.


When I can get it to start by disconnecting the MAP sensor the engine vacuum is about 10 inches and fluctuating badly. The engine will not go above idle.By the vacuum reading and the way it runs I am beginning to think that it jumped time. The engine has less than 90k miles and 175lbs. compressionon all8 cylinders. I know it is possible to jump time but the car has low miles and has not been driven hard.

I would appreciate any suggestions you guys might have before I take the timing cover off.

 

From what you are saying, it sure seems you know a lot more about these new (sensor/computer era) engines than I. But I rememeber in the good old days the three things to be checked if a no start were fuel, spark, and timing. Looks like you did two out of three so far. On my 93 it seems like an impossibility to do the following w/o a hoist or something, but not being familiar with an L98 maybe not. Anyway, we used to take out #1 plug and put the pressure tester(or a finger) on it until it hit full compression. Then look on the harmonic balancer or whatever where TDC is marked for # 1 There used to be a line there. Again, I don't even know if the line is there anymore on new engines. If the line was reasonably close to the timingplate you're in the ballpark. Then take off the distributer cover and see if the rotor is near #1 on the cap. If these two indicators are not close, I guess off comes the timing cover. GOOD LUCK.

 

Another thing. If it turns over real fast, odds are the timing chain broke.

 

If you have that good of a compression reading on all eight jugs I don't think the timing is an issue, more so since their all the same. I'm not familar with the new stuff, if the timing jumped would you have interference between the pistons and valves?

 

Thanks for the response....I just came in from the garage. I started taking the front end off the engine to get to the timing cover. Not such a bad job. All that is left is to remove the harmonic balancer, timing cover and drop the oil pan a little to get the timing cover loose.

It was pretty hot in the garage and the guy came on the radio and said make sure ya drinl lotsaliquid 'cause the temp is 107. That just totally discouraged me. I had to stop and get a drink. Opened up the fridge in the garage and all that was in the fridge was Bud Light. Darn the bad luck. Sure does taste good though. Glad the guy on the radio remined me to drink lotsa liquid.

The timing chain is not broke cause the engiine tries to fire, and the valves will not intersect the pistons on the L98. I know it is a lot of work to get to the timing chain but I am at my wits end. 1 or 2 teeth on the cam would certainly cause the problems I am having.

Will finish removing the timing cover tomorrow. It will be hot again and we can't buy beer on Sunday before 10:30 a.m., better stock up tonight it might be a long day tomorrow.

 

What do ya mean djack, you don't have A/C in the garage? I have a pretty good deal with my buddy, I put a frankenstein A/C system in his pole barn shop and I get to use the shop including the hoist whenever I need it. Man, 107 degrees, thats pretty warm, good thing it's a DRY heat, bet you've only heard that a thousand times. Good luck with the timing chain.

 

This bothers me. That, and disconnection of the MAP sensor. Whether it bothers your ECM, I don't know. But the most ancillary functions are given creedence by the ECM, and can make the ECM compensate in ways that can't be determined without a computer connected to the ALDL, and getting a reading of all functions.

L98 motors have vacuum problems all too frequently.

If there's a problem, you gotta' fix what you know ain't right, before anything else - blocked off vacuum...

 

Timing cover is off and the marks line up. Anyone ever tried to take a timing cover off a C4 with the engine in the car? If you are ever in doubt; go for it the job wasn't that bad. Plus I still have beer in the refrigerator and only a couple of small scrapes on my hands.

The engine is pristine absolutely no sludge are signs of wear.

Now I will be able to clean the externall grease and grime off the valve covers, water pump, timing cover and all the other stuff that was removed.It should look alot better when I am done.

The only problem is that I still don't know why the engine won't run.

Back to the previous post about the MAP sensor being disconnected. I only did that 'cause the GM shop manual said the disconnect it and see if the engine ran better. It did run better but still would not go above idle. The air canister purge solenoid is bad and the vacuum is blocked off as I said earlier. I found that while looking for the "no start" problem. The air canister is used for fuel vapor recovery and at this point I don't care if the vapors are recovered or not. The air canister purge solenoid usuallly only operates when the engine is cold and the fuel vapors don't all make it to the combustion chambers.The solenoid only cost about $25 dollars and I will replace itbefore the car is back on the road.

Gotta get the car fixed soon the wife is driving my pick-up and I an afraid she will start putting girly bumper stickers on it.

I would still appreciate any suggestions and thank everyone whohas responded thus far. I STILL NEED HELP!!!!!

 

Well, at least you had the good sense to take a time out and have a Bud Light or more, just like I have had today. MECH 259 willin all likelyhood have the answer for you. In the meantime, keep plugging away. By the way,the temp up here in northern WISwas81 and humid this moring, down to 75 now. Beats the hell out of 55 with the Lake Superior wind a few days ago.

 

The evap cannister does NOT purge on a cold motor. This might or might not be related to the no-run condition. I know that's a fact tho'. The ECM does not take any action on variable motor functions until the exhaust temp is 600 degrees. That is called the closed-loop mode (as opposed to the open-loop mode).

Do you know that the purge solenoid is bad? Or is the vacuum bad to the purge diaphragm, as it is told to purge? If the vacuum is getting out somewhere (or in), you'll be wastin' $$$ buyin' a new solenoid, AND you COULD still be dodgin' the source of the no-run.

I think your problem is vacuum-related - in total, if not in part. Your car/your call.