intermittent no start issue

ok i have a 89 xj 4.0 aw4. i got it off a friend of a friend who was out todling around in a field when it went from running to not running(the guy is a idoit) so he took it to his mechanic brother who in the process thought the head was warped or the head gasket was bad. he took the head off and then let it sat for like 5 months. then i got it. i got a new renix head and had it cooked magnifluxed and gone though.

ok here comes the interesting part. i put the factory intake and exhaust manifolds to the new head and it started right off revved fine and every thing. the exhaust manifold was broken. so instead of driving it around i left it at my friends shop while i waited for my 92 ho apn header. and while i was at the whole modding thing i picked up a 99+intake. i mounted all of it to the new head along with some ho injectors from a 92, and this is what i got.
http://www.youtube.com/watch?v=TPjA1oLbGI8

so i figured the injectors were messed up and put the renix ones back in. and tried it again
http://www.youtube.com/watch?v=rtCSovA_z9w
there was a leak a fuel leak at one of the injectors. but it started, it would want to die every time i opened the throttle but it started. figured it was good so i finished the tps mod to the ho tb , fixed the leaky injector and tried it again. this time it was doing the same thing it was doing with the orange top injectors.

so i started probing around looking for a reason why this is doing what it doing. i replaced the cps and noticed its not getting any volts the sensor and same for the plug to the dizzy. no power not even while cranking.

so im :banghead: and have no idea what to do. going to the junk yard in a few days. was thinking of getting a coil and ignition control mod as well as a new main ecu. my only other option is to :explosion:flame:

I had problems with my 88, it would start but then die right away, if I held the ignition it would stay running but it was killing my starter. I replaced the breakers under the hood, rotated my AC breaker with the Fuel pump and it has been running fine ever since. I don't know if that helps you, but I would look at a simple and cheap fix over replacing random expensive items like ECM's, coils and such.

ya i checked the relays they seemed fine. its getting a steady 40psi fuel pressure

It would be useful to know why it stopped running in the field in the first place, to know whether the whole thing was misdiagnosed at the start.

Before going too much further in modifications or throwing more parts at it, I think it might be a good idea to get an ohmmeter going and start tracing wires and connectors. Especially if your 88 has the notorious "C-101" connector on the bulkhead for the fuel injection harness, it's possible that a wire, a splice, or a connector has gone bad, especially if it's sat around for a long time corroding, or if the previous owner cooked the engine enough to warp the head.

Have you checked compression?

its a 89 and i dont know if has that plug or what it looks like. haven't done a compression check. the main problme here is its over a hr to get to the jeep again. i will be going down next wednesday again with some friends. just looking for more things to check

aperntly i dont have the bulkhead connection

I believe 88 was the last year of the C101.

However, if the brake/clutch MC is leaking the brake fluid will run down and contaminate the fuse block causing all kinds of problems.

The Renix--even a hybrid like yours--is ultra un-forgiving of poor grounds. The head to firewall strap is a POS, replace it with a 4 ga cable and make sure to clean down to bare metal and treat with an anti-corrosion product and then make the connections tight.

As the head-firewall is the only unibody ground, adding another ground from the negative battery terminal to the fenderwell is a good idea.

The dipstick tube--only a "Higher Power" knows why--has critical grounds for the ignition. Make sure they are clean, treat with anti-corrosion, and make them tight.

Once you have gone through all of that, post back with results.

oh never thought of checking the ground straps. ill add it to the list. 2 other things i remeber testing was the harness side of the distributor plug with a test light. no power on any of the 4 terminals not evenwhile crank. also had a weak spark

ok so first thing i checked was the head to chassis ground. of course i didnt connect it when i put the head on and that seems to have been causing the issue
but its still a hard crank start. what should i look at next?
http://www.youtube.com/watch?v=Ia7BklUdOyY

Remove that strap you just reinstalled. Scrape the paint from under the bolt that holds it to the firewall. Disconnect it from the head and clean and polish up the stud and eyelets. Reinstall. Then, go over to the engine dipstick tube and remove, clean, scrape paint and reinstall that connection securely.

A little worse than most Renix XJs.

The Renix has to "wind up" to 300 RPM with the starter before the CPS/CKP generates a large enough impulse to the ECU to fire up.

Your cranking sounds a little weak.

More powerful battery, new/fresh reman starter, 4 ga cables with clean and tight connections--all of these things will make a large improvement in starting of the Renix.

joe_peters said:

A little worse than most Renix XJs.

The Renix has to "wind up" to 300 RPM with the starter before the CPS/CKP generates a large enough impulse to the ECU to fire up.

Your cranking sounds a little weak.

More powerful battery, new/fresh reman starter, 4 ga cables with clean and tight connections--all of these things will make a large improvement in starting of the Renix.

Click to expand...

I always thought it was a matter of requiring four crank revolutions before the CPU sends out a spark signal. Then again, I might have gotten that from the same Chilton manual that says that it fires all 6 injectors simultaneously, which others convincingly assert is not true. Either way, voltage drop undoubtedly makes it worse, so I'd look there next. But don't ever expect a Renix XJ to fire up without a few spins, no matter how healthy it is.

+1
In addition, I alway turn the key on and wait for the fuel pump to quit before cranking.

I would consider replacing your injectors. Way too old! Mine started better and faster with replacements.

How do you tell if you have a weak spark? I see a spark, I have pressure at the rail and smell gas, but no start.

check the groun from hte head to the fire wall.

i had a sparkplug spark checker thingy from harobor freight. it goes between the wier and plug. has a little light in it when that cylinder is suposed to spark. if its dim weak spark bright is good spark

smcdonaldaz said:

How do you tell if you have a weak spark? I see a spark, I have pressure at the rail and smell gas, but no start.

Click to expand...

Use a spare spark plug pull one of the plug wires and attach it to the plug, ground the plug to the block and have someone try and start the engine while you observe the spark.

Spark should be blue and "snappy"--a hot spark.

Want to share anymore details on your problem?

Began to take longer to start and sputtered when it did. Pulled the cap and the spring loaded center post was worn and the end of the rotor was rough so I filed it a bit and it got started but was the same. Got back from a trip and my son says it won't start at all now. I put in a new cap and rotor and it's the same. The CPS is about 18 months old. Up until the 'no start' i was thinking leaky injector or a check valve. Now I'm leaning toward a coil. I pulled a wire and the spark wasn't snapping at all.

I've been trying to read all slow start posts but when I read "weak spark" it got my attention so i popped into the thread. Sorry if I'm hijacking.

One more thing that makes me think spark. It cranks nice and strong and every 5-7 seconds there's a slight try of a start then nothing again.

smcdonaldaz said:

How do you tell if you have a weak spark?

Click to expand...

By the color of the spark.

You are looking for a strong, blue, snapping spark. Yellow or orange spark indicates a weak spark which may not be strong enough to start the engine.

smcdonaldaz said:

How do you tell if you have a weak spark? I see a spark, I have pressure at the rail and smell gas, but no start.

Click to expand...

Spark should snap a strong blueish white. Red is weak.

Anything electrical start with the battery. Pull the cables from the battery's terminals and charge the battery overnight (Ok), or for 24 hours (Best). While the battery is charging pull the cables completely off the vehicle. Clean both ends of each cable, then test both of the cables with an ohm meter--resistance should be nearly ZERO, if not replace the cable(s). Along with this is a good time to renew all of your grounds, with particular attention to the dipstick grounds as well as the head to firewall ground strap. I recommend replacing the braided ground strap, they are problematic and should be replaced with a 4 ga cable. When renewing grounds make sure the mounting points are stripped down to bare metal, treat with an anti-corrosion product (any hardware/paint store), and are good and tight.

Now have the fully charged battery load tested. Now put everything back together--tested/new battery, cleaned/tested/new cables, and renewed grounds.

Now test the spark.