8-Track Posted February 26 Share Posted February 26 1990 Reatta, Delco ignition I have no idea why, but my mileage is absolutely crap. I checked all the plugs, they look good. Tried 2 different sets of coils and ICMs, no change. She does idle a bit rough, but not horribly. I was thinking fuel injectors, but the plugs aren't fouled. Fueled up the other day, and was 9.9 MPGs. What are some issues that could cause that? Link to comment Share on other sites More sharing options...
Ronnie Posted February 26 Share Posted February 26 Only thing that comes to mind to make mileage that bad is the engine isn't running on all cylinders. Could you possibly have gotten the spark plug wires crossed when swapping coils? 1 Link to comment Share on other sites More sharing options...
8-Track Posted February 26 Author Share Posted February 26 6 minutes ago, Ronnie said: Only thing that comes to mind to make mileage that bad is the engine isn't running on all cylinders. Could you possibly have gotten the spark plug wires crossed when swapping coils? Yeah, I triple checked them, and she doesn't seem to be missing at all Link to comment Share on other sites More sharing options...
Ben Bruce aka First Born Posted February 27 Share Posted February 27 5 hours ago, 8-Track said: 1990 Reatta, Delco ignition I have no idea why, but my mileage is absolutely crap. I checked all the plugs, they look good. Tried 2 different sets of coils and ICMs, no change. She does idle a bit rough, but not horribly. I was thinking fuel injectors, but the plugs aren't fouled. Fueled up the other day, and was 9.9 MPGs. What are some issues that could cause that? A leaky gas tank. That engine is a fuel miser. I don't see how it could run using that much gas. Ben 1 Link to comment Share on other sites More sharing options...
2seater Posted February 27 Share Posted February 27 Did the ignition system get bolted down solidly? (This is from a previous post) Have you checked for spark at each coil output? It has been proven that the 3800 will run on only two cylinders. How old is the O2 sensor and does it work? Check the vacuum line to the fuel pressure regulator for any signs of fuel. A blown diaphragm will drink unmetered fuel. Lastly, have you checked fuel pressure? Not just the running pressure but also to see if it bleeds down rapidly possibly indicating a leaky injector, (among other things) Link to comment Share on other sites More sharing options...
8-Track Posted February 27 Author Share Posted February 27 48 minutes ago, 2seater said: Did the ignition system get bolted down solidly? (This is from a previous post) Have you checked for spark at each coil output? It has been proven that the 3800 will run on only two cylinders. How old is the O2 sensor and does it work? Check the vacuum line to the fuel pressure regulator for any signs of fuel. A blown diaphragm will drink unmetered fuel. Lastly, have you checked fuel pressure? Not just the running pressure but also to see if it bleeds down rapidly possibly indicating a leaky injector, (among other things) Yeah, it's all bolted down now. I cleaned off everything for good electrical contacts, cleaned a bunch of grounds too. No idea how old the O2 sensor is, I figured it would throw a CEL if it were that. Ooohhh, I didn't think about the fuel pressure regulator, I'll look at that. Wouldn't one of the plugs be super fouled if it were a leaky injector? Link to comment Share on other sites More sharing options...
EmTee Posted February 27 Share Posted February 27 17 minutes ago, 8-Track said: I figured it would throw a CEL if it were that. Not necessarily - it could be 'lazy'... As long as it outputs a voltage within the expected range the PCM won't set a fault code. Check for vacuum leaks; the PCM could be trying to cover a lean condition caused by a vacuum leak. Check at all of the hoses and try shooting some carburetor cleaner along the intake manifold gaskets (hint: is there evidence of any coolant seepage at the intake manifold/head interface?). 2 Link to comment Share on other sites More sharing options...
Barney Eaton Posted February 27 Share Posted February 27 Check the cam sensor (magnet)..... if it is missing mileage and performance will suffer. 2 Link to comment Share on other sites More sharing options...
rogold99 Posted February 27 Share Posted February 27 Might check the knock sensor, I have been told if it goes bad it will keep ignition timing retarted, causing low power and gas mileage. 1 Link to comment Share on other sites More sharing options...
DAVES89 Posted February 27 Share Posted February 27 I'm betting on the O2 Sensor. 1 Link to comment Share on other sites More sharing options...
8-Track Posted February 27 Author Share Posted February 27 Well, got a fuel pressure tester. Read about 37-38 pounds consistently, didn't bleed off fast either, though isn't it supposed to be 40-50? However, when I started spraying carb cleaner around, I got nothing UNTIL I sprayed around the EGR valve, which instantly made the car stumble and stall. So I'm gonna pick up some gaskets and see how that affects it. 1 Link to comment Share on other sites More sharing options...
Barney Eaton Posted February 28 Share Posted February 28 Good suggestion on the knock sensor, I had that problem when I drove my 91 to Allentown in 2016 When I got home and did some diagnostics, the knock sensor showed up. Went to the pick n pull and got several and the first one I tried fixed the problem./ Link to comment Share on other sites More sharing options...
2seater Posted February 28 Share Posted February 28 (edited) 14 hours ago, 8-Track said: Well, got a fuel pressure tester. Read about 37-38 pounds consistently, didn't bleed off fast either, though isn't it supposed to be 40-50? However, when I started spraying carb cleaner around, I got nothing UNTIL I sprayed around the EGR valve, which instantly made the car stumble and stall. So I'm gonna pick up some gaskets and see how that affects it. That fuel pressure with engine running is normal. With the key on and the engine off, normal pressure is ~43.5psi It looks like all is normal there. There are three independent solenoid valves in the EGR assembly. When you remove it to replace the gaskets, check that they all move freely, both open and close. They will be obvious when EGR is in hand: there are light coil springs around them. Malfunctioning EGR will cause a rough idle. It is not supposed to be operating at idle speed, only while underway. Spraying around the EGR is also somewhat near the drivers rear corner of the intake manifold, possibly confusing the result. Edited February 28 by 2seater (see edit history) 2 Link to comment Share on other sites More sharing options...
EmTee Posted February 29 Share Posted February 29 Try using a Mighty-Vac to pull vacuum on the EGR port. If it doesn't hold vacuum, then the diaphragm is bad and that will cause a lean condition. While the valve is off, clean the pintle with carburetor cleaner and make sure it closes without sticking. 2 Link to comment Share on other sites More sharing options...
8-Track Posted March 8 Author Share Posted March 8 (edited) Well, it wasn't the EGR valve Still stalls when I hit her with the carb cleaner, so it must be the lower gasket on that adapter plate to the intake But I don't know what to look up to find the gasket. Anybody know what key words tricky phrases I need to search to find it? Edit Figured it out, actually had the gasket already No vacuum leak at the EGR anymore, but she seems to run even worse Edit 2: My roommate found a slight vacuum leak in the hard vacuum line next to the upper motor mount. Could explain the hard shifting too, but it's not big enough to stall the engine this time Edited March 8 by 8-Track (see edit history) Link to comment Share on other sites More sharing options...
2seater Posted March 9 Share Posted March 9 It seems the target keeps moving? Disconnect the harness plug from the MAF and see if it runs better. The O2 sensor is still an open question but mileage that poor and often black smoke at idle can be a MAF sensor defect. Won't necessarily set a code if it still works, but out of range. It is not unusual for the engine to stall if the MAF is connected/disconnected with the engine running, but it won't hurt anything. 1 Link to comment Share on other sites More sharing options...
rogold99 Posted March 9 Share Posted March 9 Maybe the transmission shift modulator has an internal vacuum leak? it would cause hard shifting too. Usually some transmission fluid gets sucked up by the vacuum thru the shift modulator and gets burned in the engine. Might check the tranny fluid level. Link to comment Share on other sites More sharing options...
60FlatTop Posted March 10 Share Posted March 10 Did you put the car in Neutral and see how hard it was to make it roll? 1 Link to comment Share on other sites More sharing options...
Century Eight Posted April 9 Share Posted April 9 Seems pretty basic, but how do you know your wires are still good? I just tested my wires on an old Buick and found two of them bad, and the car still running, but rough. I’ve even seen new wires fail right out of the box. Link to comment Share on other sites More sharing options...
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