[98gcawd]

First a little background. The van has 261,000 miles on it and had the original fuel pump. I drove 65 miles to work running great until I got there when I noticed an erratic idle, like hard missing, especially when in gear. On the way home, The idle seemed to smooth out at stops and it ran strong on the freeway until about 30 miles from home when it suddenly cut out, then abruptly took off again, cut out, ran again three times until it finally died. Tried several times to restart and each time it would fire, idle at 400 RPM for a few seconds then die. Towed it home and tried starting the next day and it ran long enough to move it in a better spot and then it quit for the last time.
Today I installed a new pump module that I have had for years and it started no problem, drove it out of the driveway, got on it in first gear and it backfired a couple times. Turned around in the street drove back home and it backfired again. There's no CEL and I key dance checked for codes anyway and couldn't get any. After checking for codes I started it, put it in gear and and got on the gas and it backfired and stalled. Started it again and it pulled strong. Not sure I want to get too far from home until I get it figured out. When it was running erratically at work I thought I was getting a strong exhaust smell. Where do I start? Did running erratically damage the cat?

 

[chuckt]

I had the 89 Caravan backfire and when it took out the CAT, I could tell because the exhaust was plugged so the van sonded awful with no pep;hardly made it to the muffler shop. The next day was even worse since they had a bunch of so-called automotive techs that were just a bunch of cowboys. I got the call that only the muffle was damaged and they installed a new one. Got to the shop in the evening and paid the bill. Got in and started it then tried to drive off. The van would not go over 2 mph on the road. Drove it for about 200 feet, parked it and walked back to the shop. Oh it must be the CAT (yeah, didn't you notice that you could not drive it?)! was the manager's exclamation. So, without further ado, they changed the CAT and all was well. ps-never went near that national-chain muffler shop again.
So, you would notice a failed CAT.
Since you mention that you get a back fire upon accelerating/decelerating, I would suspect a worn timing chain (you probably have the original). Speeding up and seeeing if one had a hesitation or back fire was an old test for timing chains in the v-8's. AsI recall, the 3.8L has a chain rather than a belt.

 

[98gcawd]

When I say "backfire" it's not a ka-pow out the tail pipe. It sounds like it's coming from the front, possibly thru the intake. I had a Scout II with a V8 that had flattened some cam lobes and it would pop-pop-pop thru the carb when accelerating. The timing chain is the original in the van and yes it has a lot of slack which I noticed when I changed the oil pan gasket. I was hoping I wouldn't have to do that repair but with a 2 month lay-off I won't be replacing the van anytime soon! When the van was doing its on-off-on-off-on thing while dying at 65 mph I was trying to get past a semi and over to the shoulder before someone ran me over. Maybe all that abrupt power off, power on action did it in. I guess it's time to change it and fix that timing cover/crank oil leak.

 

[John Wood]

Did you also change the filter? a 98 should have the external filter. Maybe some debris from the old pump got in the filter when it failed. It never hurts to change the fuel pump relay when replacing the pump just in case the relay contacts are burned and the contacts are intermittant.

Was this fuel pump just new 'old stock', or was it a used fuel pump?

 

[98gcawd]

No, didn't change the filter since I had done it recently. Not a bad idea to change it. You just want me to have to crawl back under there to mess with the tank again, don't you! The pump is New Very OLD Stock I bought over 9 years ago when the fuel pump suddenly got real loud. It quit making noise before I replaced it and lasted another 160,000 + miles! I'm going to bite the bullet and replace the timing set because I do know that's real loose and the water pump is seeping so I'll do both.

Thanks for the replies

 

[PCRMike]

Ditto on the cat, but that SHOULD also throw O2 sensor codes.

 

[98gcawd]

I spent the afternoon tearing it apart, oh boy was that fun :thumbsdown: There is a lot of slop in the timing chain but the wear on the gears isn't too bad. I would guess that the play mid way between the gears is 5/8" to 3/4". The Haynes manual says the max play is 1", that seems like way too much. Tomorrow morning I will track down parts and hopefully get it back together and pray that it runs better!

 

[98gcawd]

Well, here goes an update. Got the timing set installed and everything back together and it still backfired thru the intake. Now I have more noise coming from the accessory end of the engine. So I pulled the serpentine belt and started the engine and it was much quieter. The only belt driven accessory that changed is the new water pump - yippee. I then went ahead and installed a new fuel filter as recommended and it still backfired. I bought a fuel pressure test gauge and the pressure is good. When I turn the key to on the pressure jumps to almost 50psi and when the relay shuts off it drops to 42psi. When running at idle the gauge needle rapidly fluctuates between 46 and 53psi. Bring up the engine RPMs the needle is solid at about 49psi. After doing the test today, playing with the throttle while parked I noticed a very, very, slight stumble coming off idle sometimes. So I drove it just for the heck of it and it didn't hiccup once! Huh? So today I will change the studded snow tires over to the all seasons and tomorrow drive it to church, around 50 mins total driving, a mix of twisty 2 lane and freeway, and see how it does.

 

[bguy]

Are you stranded today?

 

[98gcawd]

Do you know how long it takes to walk 20 miles? a long time! LOL, just kidding. It made it but something is not right. While waiting for a pump at the gas station it acted up, felt like it shut off a split second? Hard to describe what it's doing. Stumbled/bucked a couple times on the drive home. Still no CEL. Hard to diagnose something so intermittent. Fuel pump relay like John Wood suggested?

 

[John Wood]

You could probably swap the relay with another similar relay in your vehicle. If there is an identical one like the high beam relay or the accessory relay, try it (both those relays get very little use in comparison). Although I have my doubts, it is such a simple thing to do, why not try it.

What seems strange to me are the fluctuations you noticed on your fuel pressure gauge. These engines have the regulator in the pump module (i.e. returnless). The pressure should always be a steady and solid amount irregardless of whether you are idling or going 100 MPH. The pump never changes speed and always produces far more output than would ever be required.

There may be an intermittant connection in the pump wiring, bad relay, or loss of sync signal to the computer (which would open the relay to the fuel pump, cutting power). Intermittant loss of signal could cause the fuel pump relay to chatter, but you should certainly feel a misfire and expect to see a PCM error code

 

[98gcawd]

Well, its not the relay. I wonder if I can rig up the test gauge and drive it to see if the pressure drops when it stumbles,without crushing the hose- is this safe to do? If its an intermittent connection what do I do, start wiggling any pump related wiring while its running?

 

[John Wood]

Wiggling pump related wiring might be your best shot.

I seem to remember a couple of posts on Allpar from one or more posters where the fuel pump wiring got chaffed under the floor or in a channel where it routes back to the tank area. I'm really stretching my memory on this one. Perhaps one of the prolific older mini-van owners and members on this board will remember (KOG?). Since it has been so many years ago, it would probably be in archives which are not really easy to search (IMHO). Perhaps try a Google search, and if I get time I'll try the same.

I take that there are still no codes stored in the computer.

Be safe and use common sense when routing a gauge to view for any driving analysis. Good clamps and close inspection to keep any fuel line away from any heat or pinching is mandatory.

 

[valiant67]

There could still be a chance the problem could be something other than fuel. If the crank sensor is intermittent it can cause stumbling and misfiring. And it won't always set a code either. Some people have also seen cracked flexplates on these vans as well. It's almost like you need to monitor fuel pressure and the crank sensor signal both to catch what happens when it acts up.

 

[John Wood]

One possible test to see if the pressure remains consistant would be to jumper the fuel pump relay (contacts 30 & 87) contacts in the PDC. That should cause the pump to run solid (and steady pressure) irregardless of sync pulse drop. Steady and solid pressure with a jumper could suggest a sync pulse issue, but if there are variations (with the jumper inplace) when starting, idling, or off, then wiring/bad connections should be looked for.

 

[chuckt]

I had an 89 Taurus wagon that was mechanically great but an electrical nightmare. I was stranded at least 4 times when the fuel pump, inexplicably, stopped. And this would happen every 4 months or so and the evidence was an inline fuse under the hood so this was not the case where I could re-start it. I became so desperate that I gave the car to a local Ford dealership for 2-3 weeks so they could drive it around and, if the problem occurred, see it for themselves. I got the call that a mechanic was driving it and the problem happened and they could still not determine the cause. I got the car back and later traded it in. I would imagine that a short was occurring. Ford; the wiring schematic showed that almost everything went through that same fuse so the fuel pump was vulnerable to any problem.
Sort of like hooking up my heart to my big toe.

 

[98gcawd]

I haven't had time to mess with it the past few days. I post back with anything I discover. Thanks

 

[98gcawd]

After a 2 month vacation from the van I'm back at it. Jumped the 30 and 87 terminals for the fuel pump relay in the PDC and it still stumbles, idles erratically. Hooked up the fuel pressure gauge and observed the needle while the engine was idling erratically and the needle was rock steady. The needle did dip slightly when the AC compressor kicked in. I removed the cover at the bottom of the trans bellhousing to inspect the flex plate. Couldn't see any obvious cracks. It is difficult to "inspect" it since there is a very small opening between the engine block and flex plate where you can barely see up to the edge of the holes closest to the crank. I assume if there are any cracks they will be in the vicinity of these holes that are closest to the crank. I could throw a crank sensor at it to see if that helps, but I've already thrown a bunch of money and time at it! I could also take it to a shop and have them diagnose it and hopefully it won't die on the way there.
How do you monitor the crank sensor signal?
I've got to get it running to either, use it again or sell it. I don't think I can get more than $500 at pick-n-pull for it. Too bad it would cost so much to ship it to the midwest since the body is good and solid and it would be a good candidate to swap in lower mileage running gear.

 

[ImperialCrown]

The crank sensor usually works OK or not at all. Running rough is probably something else.
Cracked flexplates can't usually be seen with the transaxle in the car. The cracks many times occur around the crankshaft bolt area. Sometimes it makes noise and sometimes it doesn't. The only sure-fire diagnosis is a visual inspection with the transaxle out.
Fuel pump pressure should be steady unless there is an electrical or pump/regulator problem. The vacuum-controlled regulator on the rail may deliver erratic fuel pressure if the vacuum supply is erratic, which a rough running engine will do. Disconnect the hose and read it. Contaminated fuel will kill a new pump.
This may not be a fuel issue at all and could be ignition or mechanical. What color are the spark plug tips?
A scan tool can read and watch the various sensors to help diagnose this. It may take awhile to get a fault code to come up, if one does. A good diagnosis would be a cost-effective way of getting an answer. Then you could decide from there.
Haynes manuals are next to worthless for this kind of work.

 

[98gcawd]

Plugs were done 40K miles ago using Champeen RN14PMP5s. On the three I checked the metal of the tips are dry and little black with very slight scaly build-up on the ground electrode. The center porcelain is slightly gray. The gap has increased to .058in..
Not willing to pull the transaxle on my gravel driveway unless all other possibilities have been exhausted.
I'm thinking it may be worth my while to purchase my own scan tool instead of paying someone else. I don't have any relationship with any mechanic so trust is a huge factor. I also don't have the money to pay others to do any of my stuff - vehicle, home and property.

I'm considering this PC based scan tool - http://www.scantool.net/scan-tools/obdlink-sx.html any thoughts on this one?