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barely running Northstar

2260 Views 18 Replies 4 Participants Last post by  spin
'98 Deville
Low mileage (79k)
Engine with start right up, but will barely run. Give it throttle (1/2 way) and it won't change rpm for about 3 seconds, then it takes off, but won't idle when backed off unless you feather the pedal. Burn your eyes exhaust.
Swapped MAF, ignition module; checked TPS (ohms) , glass beaded the almost new plugs, new wires.
Tried to swap ECM, but apparently they won't swap out without being reprogramed (?).
I'm at a loss...
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No. Fuel pressure (engine off) was 44#. Will check with running. Vacuum line looked ok.
The burning eyes told me that things were excessively rich.
Oh, no codes set.
BTW, how DO you get a OB2 ecm to swap from car to car. I've got eight ECM's sitting on the shelf from parts cars, and can't use them.
Why can't you swap PCM's? They do need to be from the same VIN (Y or 9).
Here's the latest. Car starts instantly. Runs 'ok' for about 30 seconds, then seems to load up. Feathering the throttle is needed to keep it running and the throttle has to be at least 1/2 way to keeping it running; rpms DON"T change (about 350-400 rpm, then it really kicks in and the rpms shoot way up. It'll die in an instant if you don't feather the throttle.
Fuel pressure is 44# at key on; 50# running. Increases to 55# with the vacuum line removed from the FPR (no fuel present at the vacuum line).
Attempt to substitute PCM, was futile. Tried PCM's from '97 and '96 .but no start. Seems the injectors are shut off.
This, I think, has something to do with the VATS. I had similar troubles a few years ago with a '96 STS that I swapped the IPC in, and ran into a similar situation. Had to have it rollbacked to the dealer, who did some software change(?) and it worked.
Help me out guys; point me to another thing to check.
I'm going to read the plugs tomorrow and do a compression check just to see what that may show.
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Oh, fuel pressure holds overnight, so no leaking injectors.
You keep mentioning the FPR. Why? Pressure too high?
If the diaphragm is ruptured, it may be dumping raw gas in the manifold causing it to run very rich.
...but the vacuum hose is dry...
OK, then you checked it. That's all I wanted you to do. It's good and not the problem.
Here's an update. Ran a compression test to see what I've got and had 60-70# compression on the front bank. WTF? Thought my gauge was shot. Then I measured the rear bank; 175-185#, all 4 cylinders. I don't believe the HG is bad ; all I can think of is, its jumped time. Is that possible? Looks like I'll be pulling the cam cover for a look.
I have never heard that happen, but it sounds about right. yeah, pull that valve cover off and check the valve timing
Mine did the same thing, except I had 0 -30lbs of compression on the front cylinders. It ended up being the pin that holds the sprocket in place on the cam shaft fell out.
Mine did the same thing, except I had 0 -30lbs of compression on the front cylinders. It ended up being the pin that holds the sprocket in place on the cam shaft fell out.
Did you bend any valves? What did you do to fix it?
Pulled the front camcover and it appears the intake cam has jumped time by about 20° (eyeballed). How can that happen? Now how do you secure the chain so as to remove the sprocket from the cam and realign ? I'm thinking of vise grips on the exhaust sprocket and chain, and another visegrip on the chain tight against the head. Anybody got a better idea?
Well after jerry-rigging a wedge to lock the chain tensioner, I realigned the intake cam, buttoned it all back up and it runs just fine. Now I havn't taken it out for a spin, but it idles fine and throttles up like it's supposed to in the garage. Now why did it jump time?
Did you bend any valves? What did you do to fix it?
Don't want to hi-jack this thread, but yes it bent every valve. When I checked the timing by taking the cover off it appeared to be in time (just eyeballed it) and I didn't see the pin missing. By the time I took the motor out it was obvious what happened. It looks like the cam must have spun about 360deg. No piston damage, just some slight marks. To fix it I got a used head from a salvage yard from a low milage vin 9. I'v put on 5000 miles since with no problems.

By the way, second time pulling the motor is much quicker.
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