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Posted by: 00 SS Aug 15 2011, 11:23 PM

My daily driver is an 88 Buick Park Ave. Lately, I've been having trouble with it running right when the engine is hot and I restart it. Almost seems to be vapor locking, but it's multiport fuel injection. Ocationally when this happens, I can bleed some "air" or maybe fuel vapor out of the schrader valve on the rail which sometimes helps, sometimes not. It starts, then idles like it's missing badly and the engine won't rev up. So far, I've been able to coax it into working and getting me where I need to go, but I at a bit of a loss as to why this is happening all of a sudden (the last week or so). The weather hasn't been too bad lately and it was certainly hotter earlier in the summer and it ran fine. It seems OK while I'm driving and after it's been allowed to cool down all the way.

The recent maintenance includes:
new fuel filter
new plugs
new coil packs and igniton contol module
Removed and cleaned injectors (really were pretty clean to begin with)

My ideas:
fuel pump is low on pressure allowing the fuel to vaporize in the rail while sitting after driving
Bad presure regulator not holding the pressure up while sitting after driving, or sticking not allowing the vapor to exit and return to the tank.

Any insight or ideads would be appreciated.

Posted by: wrencher Aug 16 2011, 02:00 AM

Your right to suspect the fuel pump by the problem you are describing.
Lots of times pumps act up on cold or hot starts only.
I'd say check the fuel pressure & go from there.
I also remember those having the old delco MAF's that failed constantly as well.

Posted by: CrashTestDummy Aug 16 2011, 12:43 PM

Yep. Possibly a fuel pump, possibly not. First steps would be to get a fuel pressure gauge and hook it up, and check the fuel pressure:
1. cold, turn key on, watch the fuel pressure when the pump spins up and then stops.
2. after that, turn the key off and watch the pressure. It should hold for a while. If you can see the pressure drop, the check valve, which is usually part of the fuel pump assembly, may be bad.
3. start and run the car, see what the pressure is.
4. remove the vacuum hose on the fuel pressure regulator and check for fuel in this line (blown fuel pressure regulator diaphram), and check to see what the pressure goes to. It should go up.

I am not sure what the pressure readings should be. You'll need to search for the info online, or get a FSM. I'm suspecting that 1. will be around 40 PSI, 3. should be around 35-40 psi, and 4. should be around 40-42 psi, but I don't know for sure.

If that all passes, try to get a ECM scan. Some autoparts places may offer it, but since it's not OBDII, your options may be limited. You should be able to get the ECM to flash out any stored codes, which may, or may not tell you anything.

Other than that, you're just throwing parts at it.

Posted by: 00 SS Aug 16 2011, 06:18 PM

Thanks guys. I ran the tests above.

Test 1. Pump runs for about 1 second and pressure comes up to about 30 psi.
Test 2. Pressure is steady, watched for about 5 minutes.
Test 3. Car starts and pressure is about 38-39 psi.
Test 4. Vaccum line is dry. Pressure comes up to 42-43 psi but the needle on the gauge is not steady, it seems to pulse rapidly in a 1-2 psi range.

Extra test. With the gauge in place, everything connected normally, and engine running, working the throttle induces a momentary pressure increase to about 42-43 psi. Loss of vaccum causes the regulator to increase pressure.

From the tests above, I think I can rule out a bad regulator. The pump might be going since the initial (key on engine off) pressure is below spec (40-43 psi according to my book). But that could also be the result of the run signal interval being so short. The book I have says it should run for about 2 seconds. It does not run that long. However, cycling the key off and on again does not result in much higher pressure. About 33 psi.

The 38-39 psi at engine running seems about right to me. How can the pump do that if it can only make 30-33 psi with the engine off? It seems that the pump may be going, but it may also be the pump controls.

Any ideas on which it may be? I'd hate to go through the ordeal and expense of replacing the pump and have it still not work and have the real problem be some stupid relay or something.

Posted by: trackbird Aug 16 2011, 06:45 PM

I'd also look at the ignition module and the coil packs. I had one of those cars and a bad coil pack can make it almost undriveable. It runs...to an extent. I've seen bad ones come off of the shelf at a parts store (I used to work at a few), so test everything and don't assume something is good because it's new. I've also seen plugs with cracked insulators that don't fire and I had one (personally) leaking around the ceremic (and another one was bad, and this was on an 88 hp 4 cyl Ford Escort), took me a while to find that.

Posted by: 00 SS Aug 16 2011, 07:13 PM

Kevin,

I have admit that the thought of the ignition being the cause did cross my mind, even with the new parts. I haven't been able to test the ignition while the problem is occuring since I replaced coils and the control module. Last time it was obvious that one of the three coils wasn't working, cyls 3 and 6 were dead and are on the same coil.

I guess I should go run it and warm it up so I can test that first.

Posted by: cccbock Aug 16 2011, 08:36 PM

I don't know anything about this car, but the pump may be seeing low voltage when the car is not running (alternator kicking out 14v) versus a low battery voltage less than 12 when the engine is off. Also the pump may be going bad and requiring more power (amps) to operate which is common in electric motors that are starting to fail. If you could find the normal operating amperage of the pump, then you could check the existing one and see if is to spec.

The 4th gen F-cars have a through body plug back by the tank which is the power source for the fuel pump. This sometimes gets boogered up and needs to be cleaned/replaced.

Just a couple more things to check out before replacing the pump

Posted by: CrashTestDummy Aug 17 2011, 03:09 PM

The lack of initial pressure may be because it's not spinning up long enough. I'm at a loss why that is, but it would seem to me 1-sec prime-time would be a little short. I'd verify your battery cables and engine/chassis grounds are all clean and tight. Perhaps there's some excessive voltage drop at key-on, making the system think the pump has run enough at prime. I do know the OEMs are notorious for wiring a lot of circuits with way too small a gauge of wire to run the accessory they are supposed to. There are a LOT of GMs out there that see a performance gain from running larger-gauge power wires to the pumps. The pump seems to last a bit longer, too.

If the thing uses a relay, I'd check/replace that. It can't be too expensive, and should certainly be easier to replace than a pump. Perhaps try this after running the wires and cables.

And just another thought: The fuel system in our 92 B4C Camaro involves the oil pressure switch. I got out of the car one day only to hear the fuel pump continuing to run with me holding the key in my hand. I popped the hood, started wiggling wires. There was a harness that went down to the oil filter/oil pressure switch area, and the pump quit. That was the last I had of that problem. If yours has such a pressure switch, perhaps it can be part of the problem somehow? Yeah, I'm grabbing at straws here.

Posted by: z28jeff Aug 17 2011, 04:23 PM

I had a very similar problem with my old 96 Jimmy. Low fuel pressure with battery power, then higher with engine running. Ended up being the fuel pump. It was giving us hard start issues for weeks (excessive cranking), then it quit on my wife all together in a mall parking lot....an hour away from home . I was able to get it running by hooking up jumper cables to a running vehicle. The extra couple volts were enough to get it going. I was able to drive it home, but once I shut it off in the driveway, it wouldn't restart. In my case it was the fuel pump.

Posted by: 00 SS Aug 18 2011, 03:16 AM

Of course, now that I'm trying to figure it out, it quits acting up. It ran fine the last 2 days. At least I've been able to burn off some of the fuel in the tank. I think it may be low enough now to be able to remove the tank without crushing myself.

Posted by: CrashTestDummy Aug 18 2011, 12:35 PM

It's just waiting to catch your wife all dressed up to go somewhere out on a rainy cold night an hour from home, and 30 minutes from her destination to completely quit working. Or worse, quit at a light while she's on her way to work one morning and you're already at work an hour away from her, not that I really know about anything like that.

Posted by: wrencher Aug 19 2011, 05:00 AM

Well 34-40 is running spec regulator connected.

I also remember the injectors being isses as well.
That year is a sequential injector fired 3.8.
But those injectors should be at least 12 ohms each HOT.
They caused issues, sputtering hard starts ECM failures if not addressed also.
Not near as common as a pump but another thing to check.

Posted by: 00 SS Aug 20 2011, 02:26 AM

I replaced the pump this afternoon. I now get a full 2 second prime run when I turn the key and I get 40 psi as well. It seem to run fine now, but only time will tell. By the way, never assume the pump pick is alway submersed when there is fuel in the tank. I had a hell of a time getting the new pump to prime. Of course, I was doing this with the back end up on ramps and about 2-3 gallons in the tank. It finally dawned on me and I added a 5 gallon can of fuel. Primed very quickly after that and fired right up. No matter how hard you try not to, it's still easy to do stupid things.

I still seem to get an intermittant SES light, but nothing seems to be wrong. And, of course, it will never do it when I have a scanner available. That's probably the next thing I'll have to buy.

Posted by: wrencher Aug 20 2011, 05:27 AM

Jump out A & B on the 12 pin diagnostic connector & have the check engine light flash the codes to you key on engine off.
Look at this diagram on this site;
( Some didn't have the ground pin & you had to ground the test terminal, but I pretty sure you 88 buick has both A & B )
http://www.troublecodes.net/GM/

Posted by: 00 SS Aug 20 2011, 03:52 PM

Can you do that while it's running? I don't think this computer stores old codes and shutting it off and restarting almost always clears the SES light. I was thinking I would get a scanner, plug it in and drive a while and see if I could capture the code(s). Hopefully, I can find a scanner that does both OBD-1 and 2 so I can use it on all my cars.

Posted by: 00 SS Aug 20 2011, 06:25 PM

Ok, I tried the jumper wire and it flashed 2 codes, 12 and 41. 12 is not listed in the any of the 88 3.8L tables, 41 is a cam position sensor loss of comunication for more than 2 seconds.

I had a 41 code a few years ago and I ended up having to tear the front of the engine apart and replace the magnet on the cam gear. But at that time, the code as constant and light never went out until istalled the magnet. The old one was missing at the time. Never did find it even after remiving the oil pan. This time, since the code is intermittant, maybe it's the sensor in the timing cover. Or worse, maybe a wiring issue.

Posted by: slowTA Aug 20 2011, 07:17 PM

Code 12 is normal, it is the lack of RPM signal or something like that. It's there whenever the engine isn't running.

Posted by: wrencher Aug 20 2011, 09:58 PM

Yep 12 is normal...
The 41 can be a problem though.
Cam sensor can cause a weird starting issue. Lack of a CKP (cam sensor)signal can keep the ECM from being able to run the injectors sequentially & it reverts to batch fire.
Check the magnet again, take the crank sensor out & look thru the hole with a small mirror.
The cam sensor is wired thru the crank sensor & then goes to the igntion module.
So check all that wiring, & the connectors.

Posted by: 00 SS Aug 22 2011, 01:53 PM

I've got about 100 miles on it since the fuel pump install now. Seems to be running fine. Starts easily every time so far. The damn SES light is still on about 5% (or less) of the time. It seems to come on for a minute or two a few minutes after cold start and then it goes out. Then it sometimes comes back for a few seconds a few minutes later. Then it seems to stay off for the rest of the trip. It did this yesterday afternoon when I drove it and again this morning. There is no apparent performance difference light on or off.

The magnet does still exist. The connectors appear to be connected and tight. I haven't had the time to check continuity and resistance on each wire yet. But I'm thinking it must be in the wires at this point.

Is it possible that it's the crank piosition sensor instead? You mentioned the Cam sensor was wired through the crank sensor. I had to replace the harmonic balance sever months ago. The new new one went right on and seemed to line up well with the sensor, maybe it needs to be adjusted or replaced?

Posted by: wrencher Aug 24 2011, 04:34 AM

It's possible the CKP (crank) sensor has a fault. As well as the igntion module.
But I am @ a loss for a way to tell you how to diagnose it.
The only way I test those type circuits is with a osillscope, not a piece of equiptment in everyone's tool box.

That intermittant of an issue it could be a connector or a sensor issue itself.
The CKP is a hall effect sensor (shutter wheel on balancer) The adjustment of the sensor is important, but as long as it's not hitting the shutter wheel & getting damaged it's not real likely it's causing it.
The CMP is obviously a magnetic pick up.
The CKP & CMP basically share power & ground.
The ignition module communicates these signals to the ECM.

Posted by: StanIROCZ Aug 25 2011, 02:14 AM

I don't remember the symptoms but FWIW I had to replaced the cam sensor in my '90 LeSabre. I followed a the trouble shooting guide from a service manual that positively ID'd the cam sensor. I replaced both parts ofthe sensor and timing chain while I was in there. Had 285k on that car before it was stolen.

Posted by: trackbird Aug 25 2011, 11:46 AM

Somebody stole a '90 LeSabre? In Detroit?

Posted by: StanIROCZ Aug 25 2011, 12:57 PM

haha I can't explain that one, other than this is Detroit and the car was in great condition.

Posted by: 00 SS Sep 14 2011, 01:47 AM

Well, I think it may be fixed. I ran out of ideas on how to diagnose it, so I started throwing parts at it. I replaced the cam position sensor first since that's what the code was. I did this Sunday and the light either burned out, or the code is has not returned. Knocking on wood and keeping my fingers crossed.