96 fuel pump relay chatter

[jack1018]

Hi, My wife's 96 transport has 220,000 km. Recently it is having problem with the fuel pump relay. It would chatter intermittently. I have changed the relay but didn't solve the problem. Any help will be appreciated. Thanks.

[LMP]

..will it do that just at KEY ON....you probably cannot confirm if that happens once the engine has started...can you? Does it have an impact on how the car behaves once started ?...WIll it keep or change the chatter if you giggle with the ignition switch ?
Normally, the pump goes ON for about 2 sec at KEY ON just to prime injectors, then stops and waits for crank sensor pulses .
Possibly a ground problem also...it would be interesting that you check voltage on the GROUND side of relay coil (between ground connector 86 and solid ground on car). Shold be steady at near 0 volt....well, while you are there, check also the hot side 85 for 12V...
www.avigex.ca/xport/fuelcontrol_iac.jpg

[jack1018]

Thanks for the response. The van wouldn't start 3 times in total so far. With the key on. The first time I didn't notice any relay chatter, but I noticed the fuel pump wasn't priming. I turned the key on and off about 3 times. It started. The second time I didn't notice the relay chatter neither and the fuel pump didn't prime. I turned the key off. Undid the gas cap. Turned the key back on. It started. The third time (last night). The relay was chattering with the key on. No fuel pump priming. Changed the relay. Same deal. Removed the relay. Jumped terminals 30 and 87 with wire. It didn't start. Put relay back in and tried for the last time. It started. All these events, it runs fine once it is started. Any ideas? Thanks in advance.

[LMP]

If the ECM hesitates turning the relay ON, may be at same time it would not prime the injectors...so running the pump by external means would give same results when the "random" condition is present.... Hard to pinpoint... Check with voltmeter for battery voltage when you turn the key on.... try to operate power windows when the chatter shows...check for that 12V post near the ABS , tighten the nut...I'd call all basic options, 12V feed, grounds, ignition switch before any other weirdies

[jack1018]

I checked the voltages and ground point as suggested and they checked out fine. This is a interesting one. There is a 33 Ohm resistance between the PCM chassis and the vehicle ground when the passenger door is opened. When the door is shut, the resistance dropped to 2 Ohm. Then I made a ground strap tieing the PCM chassis to vehicle ground. With the door open, it measured 26 Ohm. With the door closed, 0.5 Ohm. Not sure if it has anything to do with the fuel pump relay chatter. What are your thoughts? Thanks

[LMP]

OBviously a voltage develops between PCM case and car ground....and on the ohm scale, this translates into an apparent resistance value which changes depending on the actual amps circulating between the wired grounds and chassis ground. INvert the probes when making the test with the door opened: the added voltage value adds algebrically to the resistance measurement..adding or substracting with inverting the probes...so you would have 2 different ohm measurements for the same condition.
Repeat the same test using the voltage scale: you will probably measure a fraction of a volt..... However the fact that you have lowered this effect by using an additional ground strap indicates the ground connection does have some problem. IN fact, you have cut the actual resistance value by a factor of 4 (2 ohms to 0.5)...and I think this should have an positive effect

[jack1018]

Thanks for all the input. I will see how it does in the next while.

[96tsport]

Just to be clear, the engine in question is a 3.4L

Only mentioning it here in case there are differences with the 3.8 setup.

[LMP]

Originally Posted by 96tsport

Just to be clear, the engine in question is a 3.4L . Only mentioning it here in case there are differences with the 3.8 setup.

Relevant. Indeed diagram above relates to the 3.8 ; from the diagram I have for the '97 3.4, (I do not have the '96) relay setup is same, but the pump feed bypass provided by the oil pressure switch is non existent with the '97 3.4. The consequence is that the 3.8 fuel pump is driven independently of the relay once engine has started, but any relay upset would always impair the pump operation with the 3.4, unless the same oil pressure sensor used with the 3.8 was kept in '96....since it used same instrument panel as '92-95...I'll check the part #....
EDIT: well...it seems the 3.8 setup was indeed kept in '96 as ROckAuto.com lists the same oil pressure sender/fuel pump switch for the '96 3.4 (have to search in "electrical switches and relays")...but then, it also shows the same for '97, even is the diagram does not say so....mmm..I think we have gone full circle here....

[96tsport]

I've also had mixed results in the past with rockauto. Ordered a front crank seal (actually a parts store did) for another engine & they shipped a rear (tranny end) seal instead. When the order was checked out, it was correct & for a front seal; the box the rear seal came in matched the front seal part#.

Woulda required some contact with them suppose.. to sort it out.

I have a 96 FSM. I'll look for the wiring info & scan it when I have a chance.

[jack1018]

Quick update. It's been a week (500km) since I added the ground strap. The fuel pump relay chatter issue has not re-appeared. I have also noticed the ABS light that comes on periodically has also not re-appeared.

[jack1018]

Well, this past weekend. The problem of the fuel pump relay chatter re-appeared. The ground strap that I added over two months ago still attached but the resistance between the chassis ground and the ECM chassis is at 44 Ohm. I proceeded to remove the ECM from the vehicle and opened it up. I discovered that the ECM is a big heat with no ground. It is isolated from the chassis ground and the printed circuit board ground. I concluded that the ground strap that I added serves no purpose. I reattached the ECM and the relay chatter stopped. What do you think?

[yellowfiero]

Originally Posted by jack1018

I discovered that the ECM is a big heat

What does this mean? Heat sink?

[jack1018]

What I meant was the ECM chassis is a big heat sink with no ground points. Sorry for the confusion.