87 4.0...HAVING PROBLEMS! TIMING? ECU? CRANK SENSOR? PLEASE HELP!!!

hey everyone...thanks for looking!
i have an 87 xj and im having some issues with it
i bought it from a friend and it had been sittin for some time...over a year
i pumped the grapy fuel out and put in some good premium...about 5 gallons
i ran some rislome in the oil and sea foam in the gas tank...just to help clean out the crap.
i did all new wires, cap, plugs and rotor
new alternator and bat
new idler puller...no more sqeeks
cleaned the tb

at this point the engine ran good...smooth power...no smoke...started up everytime...(although it took between 4-7 cranks)


after a few days i ran through the good gas and the sea foam.
i replaced the fuel filter and added about 5 more gallons.
the first time a started it it took a sec...figured this must being a changed the filter...but as soon as i touched the gas pedal it started to run like poo.

its hard to put it into words but i would cut out imidiatley...followed by an intake backfire. like i said...all i did to it was change the filter!

i have had people tell me it could be the ecu or the crank sensor...either of which can screw with the timing. being there is no adjustment in timing by me i know its not something i did.

any help would be a huge help!

if you live in tualatin or in the area, if you could come by ill pay for your time...im just lost.

im heading to napa now to get the new crank sensor being its only a 20$ part

BEFORE YOU INSTALL THAT SENSOR...

Make sure it's not one for a 1991-up 4.0, since the two (1987-1990 and 1991-2007) are different animals entirely. They may look the same, but the later sensor will not work with the earlier controls!

There are two sensors that are used for basic timing on the 1987-1990 4.0L - the crankshaft position sensor and the SYNC/Camshaft Position Sensor. I've not heard of a SYNC sensor going bad yet - but there's always a first time, isn't there?:laugh3: However, I do know that RENIX (1987-1990) will run without a SYNC sensor - I've tested this.

The timing, once the distributor is set properly, is entirely under the control of the ECU and cannot be changed (readily.)

And, the "4-7 cranks" on startup is normal for the RENIX (1987-1990. Get used to that word - you'll be seeing it a lot...) system. Has to do with how it's programmed.

Also, issues can arise with the Throttle Position Sensor (TPS - on the throttle body, opposite the accelerator linkage) that can cause the symptoms you describe. A good "quick check" is to take an analogue ohmmeter, disconnect the sensor, connect the ohmmeter to terminal B and either A or C (marked on the shell of the connector) and run the throttle linkage by hand. You should see a smooth sweep of the gage needle as you move the throttle valve - any "hitches" or "flats" are problems that want the TPS to be changed.

Note that the test decribed above will not work with a digital meter! There are buffer circuits in digital meters that will give "false hitches" and "false flats" with known good sensors!

If you're in a hurry, the TPS can be had locally for about $100. If you're not, you can usually find them online slightly cheaper. BE AWARE that there are two types of TPS for your year - one for manual transmissions, and one for automatics (the automatic is actually two sensors in one case - half for the engine, and have for the transmission controller.) The A/T version may be slightly cheaper, and can be used with the manual transmission vehicle (you just don't use the four-pole square connector.)

thanks for that...but i thought the tps wouldnt be a problem with the timing.

i figured i would go for the cps first...waiting for the rain to clear...then go from there...i appreciate the help! ill keep you posted!

camshaft position sensor does go out, i have an 89' and just replaced it or actually the whole distributer. be sure to mark tdc before pulling it otherwise its a pain

well i did the cps...no luck...same thing again.

next i guess the cam sensor.

is there anyone out there that can help me and swap the ecu for a min. i can get a new ecu for 140 but i would rather make sure thats my problem!!!

also...would the distributer have the same effect if it went out...hearing my problem?


THANKS

maybe i should get into more detail about my problem. it starts just fine...it idles just fine...when i giv it any gas it doesnt die...it just runs poorly! you may have already got that but just in case

I5-TRANSPORTER said:

thanks for that...but i thought the tps wouldnt be a problem with the timing.

i figured i would go for the cps first...waiting for the rain to clear...then go from there...i appreciate the help! ill keep you posted!

Click to expand...

The TPS shouldn't cause any timing issues; but it does have a hand in fuel metering, which is why I mentioned it. Fuel metering can also cause stumbling issues and such that may present as a timing error...

From what I have read here my first thought was some trash got the fuel regulator and fuel injectors when you replaced the fuel filter. But if it idles perfectly, and only runs poorly when you press the accelerator then I would say 99.9% probablity the TPS is going bad. The ECU seems to use the rate of movement (acceleration rate) of the TPS signal to advance or retard timing some along with controlling the increasing the increased fuel rate in an attempt to keep up with the increased air flow that the engine sees when the throttle body is opened rapidly. I tried disconnecting my TPS once an gave it the gas and it backfired, stumbled and pucked all over the place, so it must be involved in the ECUs data crunching and timing output descisions.

www.teamcherokee.com (as I recall) has had OEM Renix TPS sensors for like $35 for the last 2 months (if they still have them).

I5-TRANSPORTER said:

maybe i should get into more detail about my problem. it starts just fine...it idles just fine...when i giv it any gas it doesnt die...it just runs poorly! you may have already got that but just in case

Click to expand...

Check your MAP sensor on the fire wall... make sure the tube from that to the throttle body is not plugged or has a crack in it... You will not need to change the cam sensor on a RENIX almost ever.. The CPS I can see once in a long while... So it starts fine and Idles, but backfires uppon acceleration... Before you go throwing parts at it like most people do these days, get a multi meter and the FSM and check the sensors first.. It will save you money in the long run..

I had a similar problem with my brothers jeep right after he bought it. His is a '90 and the guy he bought it from had tried everything to get it running and said the hell with it and sold it.

Well we dicked around trying to figure out what it was.......first he had two plug wires backwards. Fixed those but still wouldn't run. So we figured timing was off.......moved the distributor and it would pop back through the intake, move it again and it'd pop through the exhaust. We finally got it to where it would start up and idle, but once you touched the throttle it would start popping and coughing and fall on it's face.

It ended up being the crank pulley. The rubber was shot and it had slipped causing the timing to be off. I noticed where it said you had replaced that........are you 100% positive you got that back on right or on nice and tight? It may have slipped and is causing your timing to be off. Just a thought and something easy to check and rule out.

Testing write-up
Air, fuel, or spark?

Fuel filter replaced correctly? They are directional.
How much gas is in the tank? 4in. piece of rubber fuel line in gas tank spans from fuel pump to tank mount assy.

Catalytic converter? Blocking exhaust flow? Disconnect at the down pipe and go for a drive with exhaust set aside. (LOUD!!)

T.P.S., or C.P.S., Yeah could be, doubt it

Check, and clean spark plugs as well as all connections and use di-electric grease

Remove Idle Air Control (IAC) Spray with carb cleaner DON'T mess with pintle, just spray. Doubt that one too but....

Good Luck

Hey all I have picked up a 87 with a 4.0 and an auto tranny that is having the same exact issues as listed in this post. I-5 was there an end to your problem? Here's a rant on what have done. When I bought it it would not start, the PO had done plugs, wires, Ignition module, Cam position sensor and determined it to be the ECU so he sold it. I bought it and figured I would try the CPS first, replaced it with negres. Replaced the ECU and it started. I figured I would let it warm up before I went on a test run around the block. When I got in it was idling about 1k, not too much to worry about. I rev'd it and instantly it started to stumble on itself, poping and firing as though plugs were installed wrong. I examined the wires and plugs and found that they were in the correct order and nice and clean. Rant over sorry I jacked your thread but if this is an issue it is better that others can see it and fix it in the future. Thanks Andy

Edit: Oh hey one more thing I have gone through the TPS adjustment on here:
http://www.naxja.org/forum/showthread.php?t=924895&highlight=tighten+intake+renix
that ECOMIKE had posted, seems odd that you hook up to the five volt supply from the ECU to the gound on from the TCU on one measurement (got 4.1vdc w/ a DVM) and then on the second measurement its again the GND from the TCU to the TCU input (got -4.2 VDC w/ DVM). Am I missing something here, should I just do like the RENIX manual from 90 states. I saw the procedure and figured I might try it, so when it came out all snafu I figured might chase it in a schematic. I have yet to check my ground, I know its the renix killer; but it looks so clean and new.

Stihl029,
Without actually removing the dist, I would go through the procedure in the manual to replace one just to see if the rotor is in the correct position in relation to the crank.

Also, if you have a timing light, hook it up to each plug wire to see if you detect any differences in the flashing rate from one plug to another. Try that at idle, then slightly open the throttle and see if the signal starts skipping.
My '88 rebuild started just fine first time, idled nicely, but as soon as I raised the RPMs a little with the throttle linkage it started to stumble. I was getting an intermittent signal on the plug wires for cyls 3&4. In my case it was the CPS, which unfortunately dosen't help you. But at least you can see if things are running consistant on the ignition side.

As for the TPS, mark where it is located now, then move it slightly one way or the other to see if you get any improvement. Easy enough without looking at voltages. If it helps, maybe it's time to get a new one, and then set the voltge by the book.

Stihl029 said:

Hey all I have picked up a 87 with a 4.0 and an auto tranny that is having the same exact issues as listed in this post. I-5 was there an end to your problem? Here's a rant on what have done. When I bought it it would not start, the PO had done plugs, wires, Ignition module, Cam position sensor and determined it to be the ECU so he sold it. I bought it and figured I would try the CPS first, replaced it with negres. Replaced the ECU and it started. I figured I would let it warm up before I went on a test run around the block. When I got in it was idling about 1k, not too much to worry about. I rev'd it and instantly it started to stumble on itself, poping and firing as though plugs were installed wrong. I examined the wires and plugs and found that they were in the correct order and nice and clean. Rant over sorry I jacked your thread but if this is an issue it is better that others can see it and fix it in the future. Thanks Andy

Edit: Oh hey one more thing I have gone through the TPS adjustment on here:
http://www.naxja.org/forum/showthread.php?t=924895&highlight=tighten+intake+renix
that ECOMIKE had posted, seems odd that you hook up to the five volt supply from the ECU to the gound on from the TCU on one measurement (got 4.1vdc w/ a DVM) and then on the second measurement its again the GND from the TCU to the TCU input (got -4.2 VDC w/ DVM). Am I missing something here, should I just do like the RENIX manual from 90 states. I saw the procedure and figured I might try it, so when it came out all snafu I figured might chase it in a schematic. I have yet to check my ground, I know its the renix killer; but it looks so clean and new.

Click to expand...

Here is the TPS procedure paraphrased from a service bulletin:

For an 87-90 4.0:

Test is done with throttle closed, connectors connected, ignition on, engine off. Insert probes through back of connectors to make readings. Use a high impedance meter. Adjust TPS by loosening mounting screws and turning in mount.

For manual connect + probe to terminal A, and - to B. Take a reading, which should be in vicinity of 5 volts but probably lower. Note the reading well. Now move the positive probe to terminal C. The reading should be 16 percent of the previous reading.

For Automatic, use the square, 4-terminal plug. Connect probe + to terminal A, and - to D. Note reading, which should be in vicinity of 5 volts. Now move probe + to terminal B. This reading should be 82 % of the first.

Click to expand...

You could also check your ground wires. The ground strap from the back of the head to the firewall was off on my motor last year. Engine idled fine but ran badly. ECU wasn't getting a good ground.

Put that strap on and ran great. 5-90 sells upgraded kits also to provide great power and ground cables.

I5-TRANSPORTER said:

long time to reply i know but the problem was the fuel pump....thanks

Click to expand...

To finish up this thread and help those in the future while searching
Thanks for reply to my ancient PM I5-TRANSPORTER

Bouncy said:

You could also check your ground wires. The ground strap from the back of the head to the firewall was off on my motor last year. Engine idled fine but ran badly. ECU wasn't getting a good ground.

Put that strap on and ran great. 5-90 sells upgraded kits also to provide great power and ground cables.

Click to expand...

There's a reason that funky little ground strap is called "the RENIX killer..." It's the only ground reference for the ECU and chassis electronics.

Thank you for the kind words on my stuff - that encourages me to keep going. Note that there is no harm whatever to be done in actually adding another ground from the battery - post directly to the chassis. I've offered that as an option for my kits for a little while, and it's gotten consistently good reports from the field (even solved a few issues that a simple mains replacement didn't.) ChryCo added that ground in 1991, and it was actually a good idea on their part (going to OBD was not - I think. I've never been a fan of OBD-I. OBD-II makes a little more sense, but I think that's because California had less to do with the design and implementation of that. CARB essentially designed OBD-I, SAE designed OBD-II.)

Hey got Sorry Again for Hijacking the thread. I reindexed the timing. Some one else who had owned it or worked on it had the 6 oclock position...if you were standing at the front of the grill looking towards the back. How did they do it? They threw the old distributor tab away and made one out of an aluminum straight edge. Luckily I was able to re-bend it into a shape that would hold the distributor down. It runs like a Champ now; bit of a high idle but I think that is from the vaccum lines being so busted up and loosely held together with e-tape. Now I get to figure out why are there so many wires here and there that do not connect to anything. It was not the renix killer that we all love to hate, I remember when I had those issues on my other renix. It was nice to have a second renix around to compare to when I had questions. Thank you all for your assistance, sorry for the sand baggin on my part. After reindexing, in the snow and rain, I would say that its not so much of a tough job just easier if you can keep the marks dry. If you ever have a question about this please ask I was suprised how painless this was while my friend changed the injection pump on his CUCV. I know apples and oranges but that is how it went down.

arty: